CVE-2026-19553
Full vulnerability record from the local CVENow database.
Description
ssl.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.
Severity
HIGH
CVSS score
7.6
(v4.0)
Vulnerability status
Awaiting Analysis
Source identifier
Published
2026-09-30 17:16:45.880000
Last modified
2026-11-10 13:18:30.660000
View original CVE JSON
{
"id": "CVE-2026-19553",
"sourceIdentifier": "[email protected]",
"published": "2026-09-30T17:16:45.880",
"lastModified": "2026-11-10T13:18:30.660",
"vulnStatus": "Awaiting Analysis",
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "ssl.SSLContext.wrap_bio() didn't 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't 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't 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't 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't supplied."
}
],
"affected": [
{
"source": "[email protected]",
"affectedData": [
{
"vendor": "Python Software Foundation",
"product": "CPython",
"defaultStatus": "unaffected",
"modules": [
"ssl"
],
"repo": "https://github.com/python/cpython",
"versions": [
{
"version": "0",
"lessThan": "3.10.22",
"versionType": "python",
"status": "affected"
},
{
"version": "3.11.0",
"lessThan": "3.11.17",
"versionType": "python",
"status": "affected"
},
{
"version": "3.12.0",
"lessThan": "3.12.15",
"versionType": "python",
"status": "affected"
},
{
"version": "3.13.0",
"lessThan": "3.13.16",
"versionType": "python",
"status": "affected"
},
{
"version": "3.14.0",
"lessThan": "3.14.8",
"versionType": "python",
"status": "affected"
},
{
"version": "3.15.0a1",
"lessThan": "3.15.0rc3",
"versionType": "python",
"status": "affected"
}
]
}
]
},
{
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e",
"affectedData": [
{
"vendor": "Siemens",
"product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0)",
"defaultStatus": "unknown",
"versions": [
{
"version": "V3.1.7",
"lessThan": "*",
"versionType": "custom",
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}
]
},
{
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"product": "SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0)",
"defaultStatus": "unknown",
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"version": "V3.1.7",
"lessThan": "*",
"versionType": "custom",
"status": "affected"
}
]
},
{
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"defaultStatus": "unknown",
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{
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"defaultStatus": "unknown",
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{
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"lessThan": "*",
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"status": "affected"
}
]
},
{
"vendor": "Siemens",
"product": "SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0)",
"defaultStatus": "unknown",
"versions": [
{
"version": "V3.1.7",
"lessThan": "*",
"versionType": "custom",
"status": "affected"
}
]
}
]
}
],
"metrics": {
"cvssMetricV40": [
{
"source": "[email protected]",
"type": "Secondary",
"cvssData": {
"version": "4.0",
"vectorString": "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",
"baseScore": 7.6,
"baseSeverity": "HIGH",
"attackVector": "NETWORK",
"attackComplexity": "LOW",
"attackRequirements": "PRESENT",
"privilegesRequired": "NONE",
"userInteraction": "PASSIVE",
"vulnConfidentialityImpact": "HIGH",
"vulnIntegrityImpact": "HIGH",
"vulnAvailabilityImpact": "NONE",
"subConfidentialityImpact": "NONE",
"subIntegrityImpact": "NONE",
"subAvailabilityImpact": "NONE",
"exploitMaturity": "NOT_DEFINED",
"confidentialityRequirement": "NOT_DEFINED",
"integrityRequirement": "NOT_DEFINED",
"availabilityRequirement": "NOT_DEFINED",
"modifiedAttackVector": "NOT_DEFINED",
"modifiedAttackComplexity": "NOT_DEFINED",
"modifiedAttackRequirements": "NOT_DEFINED",
"modifiedPrivilegesRequired": "NOT_DEFINED",
"modifiedUserInteraction": "NOT_DEFINED",
"modifiedVulnConfidentialityImpact": "NOT_DEFINED",
"modifiedVulnIntegrityImpact": "NOT_DEFINED",
"modifiedVulnAvailabilityImpact": "NOT_DEFINED",
"modifiedSubConfidentialityImpact": "NOT_DEFINED",
"modifiedSubIntegrityImpact": "NOT_DEFINED",
"modifiedSubAvailabilityImpact": "NOT_DEFINED",
"Safety": "NOT_DEFINED",
"Automatable": "NOT_DEFINED",
"Recovery": "NOT_DEFINED",
"valueDensity": "NOT_DEFINED",
"vulnerabilityResponseEffort": "NOT_DEFINED",
"providerUrgency": "NOT_DEFINED"
}
}
],
"ssvcV203": [
{
"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
"ssvcData": {
"timestamp": "2026-10-16T18:33:08.291056Z",
"id": "CVE-2026-19553",
"options": [
{
"exploitation": "none"
},
{
"automatable": "no"
},
{
"technicalImpact": "total"
}
],
"role": "CISA Coordinator",
"version": "2.0.3"
}
}
]
},
"weaknesses": [
{
"source": "[email protected]",
"type": "Secondary",
"description": [
{
"lang": "en",
"value": "CWE-297"
}
]
}
],
"references": [
{
"url": "https://github.com/python/cpython/commit/1697ea386c707142555d98a1263176bbbc014a96",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/commit/5867d4e4ae6d1062352baf6b497a4026e8578ccf",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/commit/641390146a16a38e6701923f4ee4f1940ae77082",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/commit/869069d52ce0efab2f8c38197e92cdaaa312f1ed",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/commit/966bf426d0b6c31c1b0a255ff14a17143a466ced",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/commit/bdebbf9b366ec91e9cd9daa0b3510c9e84b60b80",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/commit/f4e43ba525187282f2011da0e6ffc0d2b08d8062",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/issues/156793",
"source": "[email protected]"
},
{
"url": "https://github.com/python/cpython/pull/158503",
"source": "[email protected]"
},
{
"url": "https://mail.python.org/archives/list/[email protected]/thread/QNZRG3YOAMTHDCMVCICXGY6YEFPY2VDL/",
"source": "[email protected]"
},
{
"url": "http://www.openwall.com/lists/oss-security/2026/09/30/16",
"source": "af854a3a-2127-422b-91ae-364da2661108"
},
{
"url": "https://cert-portal.siemens.com/productcert/html/ssa-457936.html",
"source": "0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"
}
]
}