GHSA-XX9W-QM94-HGHJ
Vulnerability from github – Published: 2026-09-30 18:33 – Updated: 2026-10-01 03:31ssl.SSLContext.wrap_bio() didn't require the server_hostname argument to not be None if ssl.SSLContext.check_hostname was set. Due to a missing parameter check in SSLObject, if the server_hostname argument isn't supplied then hostname verification would be silently skipped.
This defect could lead to programs where certificate hostname verification appeared to be succeeding with SSLContext.check_hostname = True and no ValueError being raised due to misconfiguration.
If the program passes a server_hostname value that isn't an empty string or None to any of these APIs then certificate hostname verification proceeds as expected and the program is not affected by this vulnerability.
Mitigating this vulnerability doesn't require updating Python or applying the patch. To mitigate, pass a valid non-None and non-empty server_hostname value to SSLContext.wrap_bio(), asyncio.create_connection(), or asyncio.loop.start_tls() and certificate hostname verification will proceed as expected. Upgrading to the latest version of Python or applying the patch only changes the behavior from silently skipping hostname verification to raising a ValueError, similar to SSLContext.wrap_socket(), when server_hostname isn't supplied.
{
"affected": [],
"aliases": [
"CVE-2026-19553"
],
"database_specific": {
"cwe_ids": [
"CWE-297"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-30T17:16:45Z",
"severity": "HIGH"
},
"details": "ssl.SSLContext.wrap_bio() didn\u0027t require the server_hostname argument\nto not be None if ssl.SSLContext.check_hostname was set. Due to a\nmissing parameter check in SSLObject, if the server_hostname argument\nisn\u0027t supplied then hostname verification would be silently skipped.\n\n\nThis defect could lead to programs where certificate hostname verification\n*appeared* to be succeeding with SSLContext.check_hostname = True and no\nValueError being raised due to misconfiguration.\n\n\nIf the program passes a server_hostname value that isn\u0027t an empty string\nor None to any of these APIs then certificate hostname verification\nproceeds as expected and the program is not affected by this vulnerability.\n\n\nMitigating this vulnerability doesn\u0027t require updating Python or applying\nthe patch. To mitigate, pass a valid non-None and non-empty\nserver_hostname value to SSLContext.wrap_bio(),\nasyncio.create_connection(), or asyncio.loop.start_tls() and\ncertificate hostname verification will proceed as expected. Upgrading to\nthe latest version of Python or applying the patch only changes the\nbehavior from silently skipping hostname verification to raising a\nValueError, similar to SSLContext.wrap_socket(), when server_hostname\nisn\u0027t supplied.",
"id": "GHSA-xx9w-qm94-hghj",
"modified": "2026-10-01T03:31:11Z",
"published": "2026-09-30T18:33:49Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-19553"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/issues/156793"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/pull/158503"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/commit/1697ea386c707142555d98a1263176bbbc014a96"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/commit/5867d4e4ae6d1062352baf6b497a4026e8578ccf"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/commit/641390146a16a38e6701923f4ee4f1940ae77082"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/commit/869069d52ce0efab2f8c38197e92cdaaa312f1ed"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/commit/966bf426d0b6c31c1b0a255ff14a17143a466ced"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/commit/bdebbf9b366ec91e9cd9daa0b3510c9e84b60b80"
},
{
"type": "WEB",
"url": "https://github.com/python/cpython/commit/f4e43ba525187282f2011da0e6ffc0d2b08d8062"
},
{
"type": "WEB",
"url": "https://mail.python.org/archives/list/security-announce@python.org/thread/QNZRG3YOAMTHDCMVCICXGY6YEFPY2VDL"
},
{
"type": "WEB",
"url": "http://www.openwall.com/lists/oss-security/2026/09/30/16"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/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",
"type": "CVSS_V4"
}
]
}
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