CVE-2026-19445 (GCVE-0-2026-19445)

Vulnerability from cvelistv5 – Published: 2026-09-30 16:16 – Updated: 2026-09-30 20:57
VLAI
Title
Use-after-free of a server-side SSLContext when sni_callback switches contexts
Summary
A remote, unauthenticated TLS client can make a server crash or call through a freed pointer if its sni_callback assigns a different context to SSLSocket.context (the documented way to select a certificate per server name) and nothing else keeps the original ssl.SSLContext alive. Typical cases are servers that create an SSLContext per connection or replace it while connections are open; servers that wrap their listening socket with it are not affected. Mitigation: keep a reference to every SSLContext that sets sni_callback for the lifetime of the server. TLS clients are not affected.
Severity
9.2 (Critical)
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Python Software Foundation CPython Affected: 0 , < 3.15.0 (python)
guessed Create a notification for this product.
Credits
Gregory P. Smith (https://github.com/gpshead) Seth Larson (https://github.com/sethmlarson) Bénédikt Tran (https://github.com/picnixz)
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "providerMetadata": {
          "dateUpdated": "2026-09-30T18:09:39.735Z",
          "orgId": "af854a3a-2127-422b-91ae-364da2661108",
          "shortName": "CVE"
        },
        "references": [
          {
            "url": "http://www.openwall.com/lists/oss-security/2026/09/30/17"
          }
        ],
        "title": "CVE Program Container"
      }
    ],
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "modules": [
            "ssl"
          ],
          "product": "CPython",
          "repo": "https://github.com/python/cpython",
          "vendor": "Python Software Foundation",
          "versions": [
            {
              "lessThan": "3.15.0",
              "status": "affected",
              "version": "0",
              "versionType": "python"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "reporter",
          "value": "Gregory P. Smith (https://github.com/gpshead)"
        },
        {
          "lang": "en",
          "type": "coordinator",
          "value": "Seth Larson (https://github.com/sethmlarson)"
        },
        {
          "lang": "en",
          "type": "remediation reviewer",
          "value": "B\u00e9n\u00e9dikt Tran (https://github.com/picnixz)"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "type": "text/html",
              "value": "\u003cp\u003eA remote, unauthenticated TLS client can make a server crash or call\nthrough a freed pointer if its sni_callback assigns a different context to\nSSLSocket.context (the documented way to select a certificate per server\nname) and nothing else keeps the original ssl.SSLContext alive. Typical\ncases are servers that create an SSLContext per connection or replace it\nwhile connections are open; servers that wrap their listening socket with\nit are not affected.\u003c/p\u003e\n\u003cp\u003eMitigation: keep a reference to every SSLContext that sets sni_callback for\nthe lifetime of the server. TLS clients are not affected.\u003c/p\u003e"
            }
          ],
          "value": "A remote, unauthenticated TLS client can make a server crash or call\nthrough a freed pointer if its sni_callback assigns a different context to\nSSLSocket.context (the documented way to select a certificate per server\nname) and nothing else keeps the original ssl.SSLContext alive. Typical\ncases are servers that create an SSLContext per connection or replace it\nwhile connections are open; servers that wrap their listening socket with\nit are not affected.\n\n\nMitigation: keep a reference to every SSLContext that sets sni_callback for\nthe lifetime of the server. TLS clients are not affected."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "HIGH",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 9.2,
            "baseSeverity": "CRITICAL",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N",
            "version": "4.0",
            "vulnAvailabilityImpact": "LOW",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "HIGH",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-416",
              "description": "CWE-416",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-30T20:57:42.815Z",
        "orgId": "28c92f92-d60d-412d-b760-e73465c3df22",
        "shortName": "PSF"
      },
      "references": [
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/python/cpython/pull/158504"
        },
        {
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://mail.python.org/archives/list/security-announce@python.org/thread/QMQIUQB6WGGC3MI7I3WKQXOYOBDSPPS3/"
        },
        {
          "tags": [
            "issue-tracking"
          ],
          "url": "https://github.com/python/cpython/issues/156293"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/python/cpython/commit/34a53dce8174da2fceb12fe084a4def02a10053d"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/python/cpython/commit/46133cd57d309652139ada74014aca7665ac552b"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/python/cpython/commit/63fab143d94cafae71850831acfb52041ba44af7"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf3698"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e2c"
        }
      ],
      "source": {
        "discovery": "UNKNOWN"
      },
      "title": "Use-after-free of a server-side SSLContext when sni_callback switches contexts",
      "x_generator": {
        "engine": "cvelib 1.8.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "28c92f92-d60d-412d-b760-e73465c3df22",
    "assignerShortName": "PSF",
    "cveId": "CVE-2026-19445",
    "datePublished": "2026-09-30T16:16:04.923Z",
    "dateReserved": "2026-08-10T13:31:21.724Z",
    "dateUpdated": "2026-09-30T20:57:42.815Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "defaultStatus": "unaffected",
                "modules": [
                  "ssl"
                ],
                "product": "CPython",
                "repo": "https://github.com/python/cpython",
                "vendor": "Python Software Foundation",
                "versions": [
                  {
                    "lessThan": "3.16.0",
                    "status": "affected",
                    "version": "0",
                    "versionType": "python"
                  }
                ]
              }
            ],
            "source": "cna@python.org"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "A remote, unauthenticated TLS client can make a server crash or call\nthrough a freed pointer if its sni_callback assigns a different context to\nSSLSocket.context (the documented way to select a certificate per server\nname) and nothing else keeps the original ssl.SSLContext alive. Typical\ncases are servers that create an SSLContext per connection or replace it\nwhile connections are open; servers that wrap their listening socket with\nit are not affected.\n\n\nMitigation: keep a reference to every SSLContext that sets sni_callback for\nthe lifetime of the server. TLS clients are not affected."
          }
        ],
        "id": "CVE-2026-19445",
        "lastModified": "2026-09-30T19:16:40.733",
        "metrics": {
          "cvssMetricV40": [
            {
              "cvssData": {
                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "HIGH",
                "attackRequirements": "PRESENT",
                "attackVector": "NETWORK",
                "availabilityRequirement": "NOT_DEFINED",
                "baseScore": 9.2,
                "baseSeverity": "CRITICAL",
                "confidentialityRequirement": "NOT_DEFINED",
                "exploitMaturity": "NOT_DEFINED",
                "integrityRequirement": "NOT_DEFINED",
                "modifiedAttackComplexity": "NOT_DEFINED",
                "modifiedAttackRequirements": "NOT_DEFINED",
                "modifiedAttackVector": "NOT_DEFINED",
                "modifiedPrivilegesRequired": "NOT_DEFINED",
                "modifiedSubAvailabilityImpact": "NOT_DEFINED",
                "modifiedSubConfidentialityImpact": "NOT_DEFINED",
                "modifiedSubIntegrityImpact": "NOT_DEFINED",
                "modifiedUserInteraction": "NOT_DEFINED",
                "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
                "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
                "modifiedVulnIntegrityImpact": "NOT_DEFINED",
                "privilegesRequired": "NONE",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "NONE",
                "subIntegrityImpact": "NONE",
                "userInteraction": "NONE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
                "version": "4.0",
                "vulnAvailabilityImpact": "LOW",
                "vulnConfidentialityImpact": "HIGH",
                "vulnIntegrityImpact": "HIGH",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "source": "cna@python.org",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-09-30T17:16:45.720",
        "references": [
          {
            "source": "cna@python.org",
            "url": "https://github.com/python/cpython/issues/156293"
          },
          {
            "source": "cna@python.org",
            "url": "https://github.com/python/cpython/pull/158504"
          },
          {
            "source": "cna@python.org",
            "url": "https://mail.python.org/archives/list/security-announce@python.org/thread/QMQIUQB6WGGC3MI7I3WKQXOYOBDSPPS3/"
          },
          {
            "source": "af854a3a-2127-422b-91ae-364da2661108",
            "url": "http://www.openwall.com/lists/oss-security/2026/09/30/17"
          }
        ],
        "sourceIdentifier": "cna@python.org",
        "vulnStatus": "Awaiting Analysis",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-416"
              }
            ],
            "source": "cna@python.org",
            "type": "Secondary"
          }
        ]
      }
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





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.



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.