GHSA-VP96-HXJ8-P424

Vulnerability from github – Published: 2026-03-16 15:15 – Updated: 2026-03-19 18:28
VLAI
Summary
pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback
Details

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.

Unhandled exceptions now result in rejecting the connection.

Credit to Leury Castillo for reporting this issue.

Severity
1.7 (Low)
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
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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "pyopenssl"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.14.0"
            },
            {
              "fixed": "26.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-27448"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-636"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-16T15:15:43Z",
    "nvd_published_at": "2026-03-18T00:16:19Z",
    "severity": "LOW"
  },
  "details": "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.\n\nUnhandled exceptions now result in rejecting the connection.\n\nCredit to **Leury Castillo** for reporting this issue.",
  "id": "GHSA-vp96-hxj8-p424",
  "modified": "2026-03-19T18:28:02Z",
  "published": "2026-03-16T15:15:43Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27448"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/pyca/pyopenssl"
    },
    {
      "type": "WEB",
      "url": "https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback"
}



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