CVE-2026-19953 (GCVE-0-2026-19953)

Vulnerability from cvelistv5 – Published: 2026-08-31 17:29 – Updated: 2026-09-01 15:16
VLAI
Title
URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep
Summary
URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep. nameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label. Any caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host.
Severity
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-01 15:16 UTC
CWE
  • CWE-1289 - Improper Validation of Unsafe Equivalence in Input
Assigner
CPANSec CNA under the redhat root
CNA scorecard C 62/100 over 346 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Affected: 0 , < 5.36 (custom)
Credits
Naseeb Dangi (naseeb0), Nankai University
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "providerMetadata": {
          "dateUpdated": "2026-08-31T20:07:50.422Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "url": "http://www.openwall.com/lists/oss-security/2026/08/31/14"
          }
        ],
        "title": "CVE Program Container"
      },
      {
        "metrics": [
          {
            "cvssV3_1": {
              "attackComplexity": "LOW",
              "attackVector": "NETWORK",
              "availabilityImpact": "NONE",
              "baseScore": 6.5,
              "baseSeverity": "MEDIUM",
              "confidentialityImpact": "LOW",
              "integrityImpact": "LOW",
              "privilegesRequired": "NONE",
              "scope": "UNCHANGED",
              "userInteraction": "NONE",
              "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
              "version": "3.1"
            }
          },
          {
            "other": {
              "content": {
                "id": "CVE-2026-19953",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-01T15:16:46.820304Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-09-01T15:16:50.672Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "collectionURL": "https://cpan.org/modules",
          "defaultStatus": "unaffected",
          "modules": [
            "URI"
          ],
          "packageName": "URI",
          "packageURL": "pkg:cpan/URI",
          "programFiles": [
            "lib/URI/_idna.pm"
          ],
          "programRoutines": [
            {
              "name": "URI::_idna::nameprep"
            }
          ],
          "repo": "https://github.com/libwww-perl/URI",
          "versions": [
            {
              "lessThan": "5.36",
              "status": "affected",
              "version": "0",
              "versionType": "custom"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "finder",
          "value": "Naseeb Dangi (naseeb0), Nankai University"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep.\n\nnameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label.\n\nAny caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host."
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-1289",
              "description": "CWE-1289 Improper Validation of Unsafe Equivalence in Input",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-31T17:29:42.929Z",
        "orgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
        "shortName": "CPANSec"
      },
      "references": [
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch"
        },
        {
          "tags": [
            "issue-tracking"
          ],
          "url": "https://github.com/libwww-perl/URI/pull/191"
        },
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://metacpan.org/release/OALDERS/URI-5.36/changes"
        },
        {
          "tags": [
            "technical-description"
          ],
          "url": "https://www.rfc-editor.org/rfc/rfc5891#section-5.2"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Upgrade to URI 5.36 or later."
        }
      ],
      "source": {
        "discovery": "UNKNOWN"
      },
      "title": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep",
      "x_generator": {
        "engine": "cpansec-cna-tool 0.1"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
    "assignerShortName": "CPANSec",
    "cveId": "CVE-2026-19953",
    "datePublished": "2026-08-31T17:29:42.929Z",
    "dateReserved": "2026-08-15T21:13:08.480Z",
    "dateUpdated": "2026-09-01T15:16:50.672Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-19953",
      "date": "2026-11-01",
      "epss": "0.00229",
      "percentile": "0.13791"
    },
    "microsoft_vex": {
      "current_release_date": "2026-09-24T02:12:14.000Z",
      "cve": "CVE-2026-19953",
      "id": "msrc_CVE-2026-19953",
      "initial_release_date": "2026-09-03T01:09:27.000Z",
      "product_status:fixed": "2",
      "product_status:known_affected": "2",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-19953.json",
      "version": "4"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "collectionURL": "https://cpan.org/modules",
                "defaultStatus": "unaffected",
                "modules": [
                  "URI"
                ],
                "packageName": "URI",
                "packageURL": "pkg:cpan/URI",
                "programFiles": [
                  "lib/URI/_idna.pm"
                ],
                "programRoutines": [
                  {
                    "name": "URI::_idna::nameprep"
                  }
                ],
                "repo": "https://github.com/libwww-perl/URI",
                "versions": [
                  {
                    "lessThan": "5.36",
                    "status": "affected",
                    "version": "0",
                    "versionType": "custom"
                  }
                ]
              }
            ],
            "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep.\n\nnameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label.\n\nAny caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host."
          }
        ],
        "id": "CVE-2026-19953",
        "lastModified": "2026-09-03T16:41:09.297",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 6.5,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "LOW",
                "integrityImpact": "LOW",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 2.5,
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-19953",
                "options": [
                  {
                    "exploitation": "none"
                  },
                  {
                    "automatable": "yes"
                  },
                  {
                    "technicalImpact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-01T15:16:46.820304Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-08-31T18:17:14.320",
        "references": [
          {
            "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
            "url": "https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch"
          },
          {
            "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
            "url": "https://github.com/libwww-perl/URI/pull/191"
          },
          {
            "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
            "url": "https://metacpan.org/release/OALDERS/URI-5.36/changes"
          },
          {
            "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
            "url": "https://www.rfc-editor.org/rfc/rfc5891#section-5.2"
          },
          {
            "source": "af854a3a-2127-422b-91ae-364da2661108",
            "url": "http://www.openwall.com/lists/oss-security/2026/08/31/14"
          }
        ],
        "sourceIdentifier": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
        "vulnStatus": "Deferred",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-1289"
              }
            ],
            "source": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-10-30T07:31:34+00:00",
      "cve": "CVE-2026-19953",
      "id": "CVE-2026-19953",
      "initial_release_date": "2026-08-31T17:29:42.929000+00:00",
      "product_status:fixed": "12",
      "product_status:known_affected": "6",
      "product_status:known_not_affected": "5",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "URI: URI (for Perl): Security bypass due to incorrect hostname encoding via missing Unicode normalization",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-19953.json",
      "version": "3"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "providerMetadata": {
              "dateUpdated": "2026-08-31T20:07:50.422Z",
              "orgId": "af854a3a-2127-422b-91ae-364da2661108",
              "shortName": "CVE"
            },
            "references": [
              {
                "url": "http://www.openwall.com/lists/oss-security/2026/08/31/14"
              }
            ],
            "title": "CVE Program Container"
          },
          {
            "metrics": [
              {
                "cvssV3_1": {
                  "attackComplexity": "LOW",
                  "attackVector": "NETWORK",
                  "availabilityImpact": "NONE",
                  "baseScore": 6.5,
                  "baseSeverity": "MEDIUM",
                  "confidentialityImpact": "LOW",
                  "integrityImpact": "LOW",
                  "privilegesRequired": "NONE",
                  "scope": "UNCHANGED",
                  "userInteraction": "NONE",
                  "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
                  "version": "3.1"
                }
              },
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-19953",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "yes"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-09-01T15:16:46.820304Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-09-01T15:16:35.917Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "collectionURL": "https://cpan.org/modules",
              "defaultStatus": "unaffected",
              "modules": [
                "URI"
              ],
              "packageName": "URI",
              "packageURL": "pkg:cpan/URI",
              "programFiles": [
                "lib/URI/_idna.pm"
              ],
              "programRoutines": [
                {
                  "name": "URI::_idna::nameprep"
                }
              ],
              "repo": "https://github.com/libwww-perl/URI",
              "versions": [
                {
                  "lessThan": "5.36",
                  "status": "affected",
                  "version": "0",
                  "versionType": "custom"
                }
              ]
            }
          ],
          "credits": [
            {
              "lang": "en",
              "type": "finder",
              "value": "Naseeb Dangi (naseeb0), Nankai University"
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep.\n\nnameprep lowercases each host label but performs no Unicode normalization. IDNA requires a label to be normalized to Form C before it is encoded (RFC 5891), so a label that is not already in NFC is encoded to a different A-label than its normalized form. A label built from the precomposed Devanagari sequence U+0958 U+093E encodes to xn--72b5c without normalization but to xn--11b2fg after NFC normalization, and xn--72b5c does not round-trip back to the original label.\n\nAny caller that reads host() from a URI built from untrusted input and uses it for a security decision (an allow or deny list, an SSRF filter, deduplication, a cache key) sees the non-standard label, while a client that fetches the same URL resolves the NFC form, so the check and the fetch can disagree about the host."
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-1289",
                  "description": "CWE-1289 Improper Validation of Unsafe Equivalence in Input",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-08-31T17:29:42.929Z",
            "orgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
            "shortName": "CPANSec"
          },
          "references": [
            {
              "tags": [
                "patch"
              ],
              "url": "https://github.com/libwww-perl/URI/commit/956619a9e94f86d8d2c529b4e06a3674c54a73e7.patch"
            },
            {
              "tags": [
                "issue-tracking"
              ],
              "url": "https://github.com/libwww-perl/URI/pull/191"
            },
            {
              "tags": [
                "release-notes"
              ],
              "url": "https://metacpan.org/release/OALDERS/URI-5.36/changes"
            },
            {
              "tags": [
                "technical-description"
              ],
              "url": "https://www.rfc-editor.org/rfc/rfc5891#section-5.2"
            }
          ],
          "solutions": [
            {
              "lang": "en",
              "value": "Upgrade to URI 5.36 or later."
            }
          ],
          "source": {
            "discovery": "UNKNOWN"
          },
          "title": "URI versions before 5.36 for Perl encode non-NFC host names to non-standard punycode labels via missing normalization in nameprep",
          "x_generator": {
            "engine": "cpansec-cna-tool 0.1"
          }
        }
      },
      "cveMetadata": {
        "assignerOrgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
        "assignerShortName": "CPANSec",
        "cveId": "CVE-2026-19953",
        "datePublished": "2026-08-31T17:29:42.929Z",
        "dateReserved": "2026-08-15T21:13:08.480Z",
        "dateUpdated": "2026-09-01T15:16:50.672Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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

JSON

Loading timeline…




    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.