pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

{
  "id": "95128524797434ba113697e3103aa40bf41ecbe49b74b3f8e365bee6fd2c0cdb",
  "url": "https://osv.dev/vulnerability/CVE-2026-27448",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback",
    "summary": "pyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 0.14.0 and prior to version 26.0.0, if a user provided callback to `set_tlsext_servername_callback` raised an unhandled exception, this would result in a connection being accepted. If a user was relying on this callback for any security-sensitive behavior, this could allow bypassing it. Starting in version 26.0.0, unhandled exceptions now result in rejecting the connection.",
    "evidence": "osv:CVE-2026-27448",
    "products": [],
    "severity": "low",
    "structured": {
      "id": "CVE-2026-27448",
      "aliases": [
        "CVE-2026-27448",
        "GHSA-vp96-hxj8-p424",
        "PYSEC-2026-2268"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/pyca/pyopenssl",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0146d447e63a737b4f05a1164d5950eff68543e7"
                },
                {
                  "fixed": "358cbf29c4e364c59930e53a270116249581eaa3"
                },
                {
                  "fixed": "d41a814759a9fb49584ca8ab3f7295de49a85aa0"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "cpe": "cpe:2.3:a:pyopenssl:pyopenssl:*:*:*:*:*:*:*:*",
                    "range": [
                      {
                        "introduced": "0.14"
                      },
                      {
                        "fixed": "26.0.0"
                      }
                    ],
                    "source": "CPE_RANGE"
                  },
                  {
                    "range": [
                      {
                        "fixed": "d41a814759a9fb49584ca8ab3f7295de49a85aa0"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27448.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:29.905127580Z",
      "provider": "osv",
      "references": [
        "https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27448.json",
        "https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-27448",
        "https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-636"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27448.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-27448",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 496584,
  "published_at": "2026-03-17T23:24:30.661+00:00"
}