Vulnerability-Lookup

CVE-2026-55568 (GCVE-0-2026-55568)

Vulnerability from cvelistv5 – Published: 2026-06-23 14:54 – Updated: 2026-06-23 15:44

Title

Guzzle: Silent HTTPS-Proxy Downgrade to Cleartext

Summary

Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. The built-in cURL handlers (GuzzleHttp\Handler\CurlHandler and GuzzleHttp\Handler\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy. libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1.

Severity

5.9 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-23 15:44 UTC

CWE

CWE-311 - Missing Encryption of Sensitive Data
CWE-319 - Cleartext Transmission of Sensitive Information
CWE-636 - Not Failing Securely ('Failing Open')

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7886 records in the last 180 days details

References

1 reference

URL	Tags
https://github.com/guzzle/guzzle/security/advisor…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version	CPE status
guzzle	guzzle	Affected: < 7.12.1	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-55568",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-23T15:44:34.695690Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-06-23T15:44:40.427Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "guzzle",
          "vendor": "guzzle",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 7.12.1"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. The built-in cURL handlers (GuzzleHttp\\Handler\\CurlHandler and GuzzleHttp\\Handler\\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy. libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 5.9,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-311",
              "description": "CWE-311: Missing Encryption of Sensitive Data",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-319",
              "description": "CWE-319: Cleartext Transmission of Sensitive Information",
              "lang": "en",
              "type": "CWE"
            }
          ]
        },
        {
          "descriptions": [
            {
              "cweId": "CWE-636",
              "description": "CWE-636: Not Failing Securely (\u0027Failing Open\u0027)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-23T14:54:23.655Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3"
        }
      ],
      "source": {
        "advisory": "GHSA-wpwq-4j6v-78m3",
        "discovery": "UNKNOWN"
      },
      "title": "Guzzle: Silent HTTPS-Proxy Downgrade to Cleartext"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-55568",
    "datePublished": "2026-06-23T14:54:23.655Z",
    "dateReserved": "2026-06-16T23:11:20.214Z",
    "dateUpdated": "2026-06-23T15:44:40.427Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-55568",
      "date": "2026-11-14",
      "epss": "0.00148",
      "percentile": "0.04042"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "guzzle",
                "vendor": "guzzle",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c 7.12.1"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "configurations": [
          {
            "nodes": [
              {
                "cpeMatch": [
                  {
                    "criteria": "cpe:2.3:a:guzzlephp:guzzle:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "F4DA5939-7C26-4452-A790-9A0457E04DE4",
                    "versionEndExcluding": "7.12.1",
                    "vulnerable": true
                  }
                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. The built-in cURL handlers (GuzzleHttp\\Handler\\CurlHandler and GuzzleHttp\\Handler\\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy. libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1."
          }
        ],
        "id": "CVE-2026-55568",
        "lastModified": "2026-06-26T19:34:13.833",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 5.9,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 2.2,
              "impactScore": 3.6,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-55568",
                "options": [
                  {
                    "exploitation": "none"
                  },
                  {
                    "automatable": "no"
                  },
                  {
                    "technicalImpact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-23T15:44:34.695690Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-06-23T16:17:02.990",
        "references": [
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Third Party Advisory"
            ],
            "url": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Analyzed",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-311"
              },
              {
                "lang": "en",
                "value": "CWE-319"
              },
              {
                "lang": "en",
                "value": "CWE-636"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "current_release_date": "2026-06-28T07:14:34+00:00",
      "cve": "CVE-2026-55568",
      "id": "CVE-2026-55568",
      "initial_release_date": "2026-06-23T14:54:23.655000+00:00",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "guzzlehttp/guzzle: Guzzle: Information disclosure via cleartext proxy communication",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-55568.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-55568",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-06-23T15:44:34.695690Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-06-23T15:44:37.292Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "product": "guzzle",
              "vendor": "guzzle",
              "versions": [
                {
                  "status": "affected",
                  "version": "\u003c 7.12.1"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. The built-in cURL handlers (GuzzleHttp\\Handler\\CurlHandler and GuzzleHttp\\Handler\\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy. libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 5.9,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
                "version": "3.1"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-311",
                  "description": "CWE-311: Missing Encryption of Sensitive Data",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            },
            {
              "descriptions": [
                {
                  "cweId": "CWE-319",
                  "description": "CWE-319: Cleartext Transmission of Sensitive Information",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            },
            {
              "descriptions": [
                {
                  "cweId": "CWE-636",
                  "description": "CWE-636: Not Failing Securely (\u0027Failing Open\u0027)",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-06-23T14:54:23.655Z",
            "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
            "shortName": "GitHub_M"
          },
          "references": [
            {
              "name": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3",
              "tags": [
                "x_refsource_CONFIRM"
              ],
              "url": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3"
            }
          ],
          "source": {
            "advisory": "GHSA-wpwq-4j6v-78m3",
            "discovery": "UNKNOWN"
          },
          "title": "Guzzle: Silent HTTPS-Proxy Downgrade to Cleartext"
        }
      },
      "cveMetadata": {
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "assignerShortName": "GitHub_M",
        "cveId": "CVE-2026-55568",
        "datePublished": "2026-06-23T14:54:23.655Z",
        "dateReserved": "2026-06-16T23:11:20.214Z",
        "dateUpdated": "2026-06-23T15:44:40.427Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

CLEANSTART-2026-SK75094 (CVE-2026-55568)

Vulnerability from cleanstart – Published: 2026-10-31 11:58 – Updated: 2026-08-14 09:39 – Source website

Summary

Guzzle is an extensible PHP HTTP client

Details

Security vulnerability affects the nextcloud package. Guzzle is an extensible PHP HTTP client.

Severity

5.9 (Medium)


                    
                      CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

References

URL

Type

	https://github.com/cleanstart-dev/cleanstart-secu…	ADVISORY
	https://osv.dev/vulnerability/CVE-2026-55568	WEB
	https://nvd.nist.gov/vuln/detail/CVE-2026-55568	WEB

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "CleanStart",
        "name": "nextcloud",
        "purl": "pkg:apk/cleanstart/nextcloud?arch=noarch"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "32.0.3-r0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "credits": [],
  "database_specific": {},
  "details": "Security vulnerability affects the nextcloud package. Guzzle is an extensible PHP HTTP client.",
  "id": "CLEANSTART-2026-SK75094",
  "modified": "2026-08-14T09:39:36Z",
  "published": "2026-10-31T11:58:07.413731Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/cleanstart-dev/cleanstart-security-advisories/tree/main/advisories/2026/CLEANSTART-2026-SK75094.json"
    },
    {
      "type": "WEB",
      "url": "https://osv.dev/vulnerability/CVE-2026-55568"
    },
    {
      "type": "WEB",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55568"
    }
  ],
  "related": [],
  "schema_version": "1.7.3",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Guzzle is an extensible PHP HTTP client",
  "upstream": [
    "CVE-2026-55568"
  ]
}

FKIE_CVE-2026-55568

Vulnerability from fkie_nvd - Published: 2026-06-23 16:17 - Updated: 2026-06-26 19:34

Severity

5.9 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3	Third Party Advisory

Impacted products

	Vendor	Product	Version
	guzzlephp	guzzle	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "guzzle",
          "vendor": "guzzle",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 7.12.1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:guzzlephp:guzzle:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "F4DA5939-7C26-4452-A790-9A0457E04DE4",
              "versionEndExcluding": "7.12.1",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. The built-in cURL handlers (GuzzleHttp\\Handler\\CurlHandler and GuzzleHttp\\Handler\\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy. libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1."
    }
  ],
  "id": "CVE-2026-55568",
  "lastModified": "2026-06-26T19:34:13.833",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 5.9,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-55568",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-06-23T15:44:34.695690Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-06-23T16:17:02.990",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Third Party Advisory"
      ],
      "url": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-311"
        },
        {
          "lang": "en",
          "value": "CWE-319"
        },
        {
          "lang": "en",
          "value": "CWE-636"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-WPWQ-4J6V-78M3

Vulnerability from github – Published: 2026-06-19 14:17 – Updated: 2026-06-19 14:17

Summary

guzzlehttp/guzzle: Silent HTTPS-Proxy Downgrade to Cleartext

Details

Impact

The built-in cURL handlers (GuzzleHttp\Handler\CurlHandler and GuzzleHttp\Handler\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy — a proxy reached over a TLS-encrypted connection — through the proxy request option, client-level proxy defaults, or proxy environment variables such as http_proxy, https_proxy, HTTPS_PROXY, all_proxy, and ALL_PROXY.

When the installed libcurl does not support HTTPS proxies, behavior depends on the libcurl version/build:

libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning.
libcurl 7.50.2 through 7.51.x rejects the unsupported proxy scheme at connect time, so no cleartext exposure occurs, but the failure is late and opaque.
libcurl 7.52.0 or newer builds without HTTPS-proxy support also fail at connect time rather than downgrading.

The security-relevant case is the silent downgrade on libcurl older than 7.50.2. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2.

In that configuration, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. For plain HTTP requests, request headers and bodies are also exposed on the proxy leg. End-to-end HTTPS requests tunneled through the proxy remain protected by their inner TLS session; the exposure is limited to the proxy negotiation and proxy credentials.

Applications that do not configure an https:// proxy are not affected. Installations running libcurl 7.52.0 or newer built with HTTPS-proxy support are not affected because HTTPS proxies work as intended. Installations running libcurl 7.50.2 through 7.51.x, or libcurl 7.52.0 or newer built without HTTPS-proxy support, are not exposed to the silent cleartext downgrade, but Guzzle now rejects those unsupported configurations up front as well. The built-in stream handler is not affected; the issue is specific to the cURL handlers' proxy handling. Low-level cURL options under the curl request option, such as CURLOPT_PROXY or CURLOPT_PROXYTYPE, are advanced custom configuration and remain the caller's responsibility.

Patches

The issue is patched in 7.12.1 and later. Starting in that release, the built-in cURL handlers detect whether the installed libcurl supports HTTPS proxies — requiring both libcurl 7.52.0 or newer and the CURL_VERSION_HTTPS_PROXY feature bit — and reject a request configured through Guzzle's first-class proxy handling with an https:// proxy up front by throwing a GuzzleHttp\Exception\RequestException. No request bytes reach the network when the proxy cannot be used securely. Versions before 7.12.1 are affected by the silent downgrade when run against libcurl older than 7.50.2.

Workarounds

If you cannot upgrade immediately, do not configure an https:// proxy on an installation whose libcurl lacks HTTPS-proxy support, and verify the capability in application code before using one. Remember to check proxy environment variables as well as any explicit proxy option:

$curl = \curl_version();
$httpsProxyBit = \defined('CURL_VERSION_HTTPS_PROXY') ? \CURL_VERSION_HTTPS_PROXY : (1 << 21);

if (\version_compare($curl['version'], '7.52.0', '<') || 0 === ($curl['features'] & $httpsProxyBit)) {
    throw new \RuntimeException('Installed libcurl does not support HTTPS proxies.');
}

Upgrading the system libcurl to 7.52.0 or newer built with HTTPS-proxy support also resolves the underlying unsupported-proxy behavior.

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "Packagist",
        "name": "guzzlehttp/guzzle"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.12.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-55568"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-311",
      "CWE-319",
      "CWE-636"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-19T14:17:59Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nThe built-in cURL handlers (`GuzzleHttp\\Handler\\CurlHandler` and `GuzzleHttp\\Handler\\CurlMultiHandler`, used by default whenever the PHP cURL extension is available) accept an `https://` proxy \u2014 a proxy reached over a TLS-encrypted connection \u2014 through the `proxy` request option, client-level `proxy` defaults, or proxy environment variables such as `http_proxy`, `https_proxy`, `HTTPS_PROXY`, `all_proxy`, and `ALL_PROXY`.\n\nWhen the installed libcurl does not support HTTPS proxies, behavior depends on the libcurl version/build:\n\n- libcurl older than 7.50.2 silently treats an `https://` proxy as a plaintext `http://` proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning.\n- libcurl 7.50.2 through 7.51.x rejects the unsupported proxy scheme at connect time, so no cleartext exposure occurs, but the failure is late and opaque.\n- libcurl 7.52.0 or newer builds without HTTPS-proxy support also fail at connect time rather than downgrading.\n\nThe security-relevant case is the silent downgrade on libcurl older than 7.50.2. An application is affected when it sends requests through one of the built-in cURL handlers, configures an `https://` proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2.\n\nIn that configuration, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the `Proxy-Authorization` header, proxy userinfo in the proxy URL, or `CURLOPT_PROXYUSERPWD`) are sent without encryption, and the `CONNECT` target host and port for tunneled HTTPS requests are exposed. For plain HTTP requests, request headers and bodies are also exposed on the proxy leg. End-to-end HTTPS requests tunneled through the proxy remain protected by their inner TLS session; the exposure is limited to the proxy negotiation and proxy credentials.\n\nApplications that do not configure an `https://` proxy are not affected. Installations running libcurl 7.52.0 or newer built with HTTPS-proxy support are not affected because HTTPS proxies work as intended. Installations running libcurl 7.50.2 through 7.51.x, or libcurl 7.52.0 or newer built without HTTPS-proxy support, are not exposed to the silent cleartext downgrade, but Guzzle now rejects those unsupported configurations up front as well. The built-in stream handler is not affected; the issue is specific to the cURL handlers\u0027 proxy handling. Low-level cURL options under the `curl` request option, such as `CURLOPT_PROXY` or `CURLOPT_PROXYTYPE`, are advanced custom configuration and remain the caller\u0027s responsibility.\n\n### Patches\n\nThe issue is patched in `7.12.1` and later. Starting in that release, the built-in cURL handlers detect whether the installed libcurl supports HTTPS proxies \u2014 requiring both libcurl 7.52.0 or newer and the `CURL_VERSION_HTTPS_PROXY` feature bit \u2014 and reject a request configured through Guzzle\u0027s first-class proxy handling with an `https://` proxy up front by throwing a `GuzzleHttp\\Exception\\RequestException`. No request bytes reach the network when the proxy cannot be used securely. Versions before `7.12.1` are affected by the silent downgrade when run against libcurl older than 7.50.2.\n\n### Workarounds\n\nIf you cannot upgrade immediately, do not configure an `https://` proxy on an installation whose libcurl lacks HTTPS-proxy support, and verify the capability in application code before using one. Remember to check proxy environment variables as well as any explicit `proxy` option:\n\n```php\n$curl = \\curl_version();\n$httpsProxyBit = \\defined(\u0027CURL_VERSION_HTTPS_PROXY\u0027) ? \\CURL_VERSION_HTTPS_PROXY : (1 \u003c\u003c 21);\n\nif (\\version_compare($curl[\u0027version\u0027], \u00277.52.0\u0027, \u0027\u003c\u0027) || 0 === ($curl[\u0027features\u0027] \u0026 $httpsProxyBit)) {\n    throw new \\RuntimeException(\u0027Installed libcurl does not support HTTPS proxies.\u0027);\n}\n```\n\nUpgrading the system libcurl to 7.52.0 or newer built with HTTPS-proxy support also resolves the underlying unsupported-proxy behavior.",
  "id": "GHSA-wpwq-4j6v-78m3",
  "modified": "2026-06-19T14:17:59Z",
  "published": "2026-06-19T14:17:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/guzzle/guzzle"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "guzzlehttp/guzzle: Silent HTTPS-Proxy Downgrade to Cleartext"
}

UBUNTU-CVE-2026-55568 (CVE-2026-55568)

Vulnerability from osv_ubuntu – Published: 2026-06-23 16:17 – Updated: 2026-10-17 09:45 – Source website

Details

Severity

5.9 (Medium)


                    
                      CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-55568	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-55568	REPORT
	https://github.com/guzzle/guzzle/security/advisor…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "php-guzzlehttp-guzzle",
            "binary_version": "7.4.5-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:24.04:LTS",
        "name": "guzzle",
        "purl": "pkg:deb/ubuntu/guzzle@7.4.5-1?arch=source\u0026distro=noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "7.4.5-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "php-guzzlehttp-guzzle",
            "binary_version": "7.9.2-0.1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:25.10",
        "name": "guzzle",
        "purl": "pkg:deb/ubuntu/guzzle@7.9.2-0.1?arch=source\u0026distro=questing"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "7.9.2-0.1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "php-guzzlehttp-guzzle",
            "binary_version": "7.15.3-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.10",
        "name": "guzzle",
        "purl": "pkg:deb/ubuntu/guzzle@7.15.3-1?arch=source\u0026distro=stonking"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "7.9.2-0.1build1",
        "7.13.1-1",
        "7.15.1-1",
        "7.15.2-1",
        "7.15.3-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "php-guzzlehttp-guzzle",
            "binary_version": "7.9.2-0.1build1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.04:LTS",
        "name": "guzzle",
        "purl": "pkg:deb/ubuntu/guzzle@7.9.2-0.1build1?arch=source\u0026distro=resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "7.9.2-0.1",
        "7.9.2-0.1build1"
      ]
    }
  ],
  "aliases": [],
  "details": "Guzzle is an extensible PHP HTTP client. Prior to 7.12.1, in certain configurations, traffic expected to be protected by TLS on the hop to the proxy is transmitted in cleartext. Proxy authentication credentials (the Proxy-Authorization header, proxy userinfo in the proxy URL, or CURLOPT_PROXYUSERPWD) are sent without encryption, and the CONNECT target host and port for tunneled HTTPS requests are exposed. The built-in cURL handlers (GuzzleHttp\\Handler\\CurlHandler and GuzzleHttp\\Handler\\CurlMultiHandler, used by default whenever the PHP cURL extension is available) accept an https:// proxy. libcurl older than 7.50.2 silently treats an https:// proxy as a plaintext http:// proxy. The TLS connection to the proxy is never established, and the proxy leg is cleartext with no error or warning. An application is affected when it sends requests through one of the built-in cURL handlers, configures an https:// proxy expecting the proxy connection itself to be encrypted, and runs with libcurl older than 7.50.2. This vulnerability is fixed in 7.12.1.",
  "id": "UBUNTU-CVE-2026-55568",
  "modified": "2026-10-17T09:45:55Z",
  "published": "2026-06-23T16:17:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-55568"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-55568"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/guzzle/guzzle/security/advisories/GHSA-wpwq-4j6v-78m3"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-55568"
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

Order JSON

How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

Publication & reservation Sightings KEV catalogs Other timestamps

Loading timeline…

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-55568 (GCVE-0-2026-55568)

CLEANSTART-2026-SK75094 (CVE-2026-55568)

FKIE_CVE-2026-55568

GHSA-WPWQ-4J6V-78M3

Impact

Patches

Workarounds

UBUNTU-CVE-2026-55568 (CVE-2026-55568)

Tags

Sightings

Nomenclature

Vulnerability timeline

Related by attack behaviour