Description
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.
Metrics
CVSS 4.0 9.2/10
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:XWeakness enumeration
Affected software
Source: the vendor's advisory (CNA). NVD analysis pending.
| Vendor | Product | Versions |
|---|---|---|
| Python Software Foundation | CPython | < 3.10.22; >= 3.11.0, < 3.11.17; >= 3.12.0, < 3.12.15; >= 3.13.0, < 3.13.16; >= 3.14.0, < 3.14.8; >= 3.15.0a1, < 3.15.0rc3 |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) | >= V3.1.7, < * |
| Siemens | SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) | >= V3.1.7, < * |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) | >= V3.1.7, < * |
| Siemens | SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) | >= V3.1.7, < * |
| Siemens | SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) | >= V3.1.7, < * |
References
- https://github.com/python/cpython/commit/34a53dce8174da2fceb12fe084a4def02a10053d
- https://github.com/python/cpython/commit/46133cd57d309652139ada74014aca7665ac552b
- https://github.com/python/cpython/commit/63fab143d94cafae71850831acfb52041ba44af7
- https://github.com/python/cpython/commit/b12968cefe69ca1dcb8606c832ff73ee7dbf4ba8
- https://github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf3698
- https://github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e2c
- https://github.com/python/cpython/commit/ec44b5a3258cbda947d5e07242ee562ed05ef24b
- https://github.com/python/cpython/issues/156293
- https://github.com/python/cpython/pull/158504
- https://mail.python.org/archives/list/security-announce@python.org/thread/QMQIUQB6WGGC3MI7I3WKQXOYOBDSPPS3/
- http://www.openwall.com/lists/oss-security/2026/09/30/17
- https://cert-portal.siemens.com/productcert/html/ssa-457936.html
Timeline
- Published
- Sep 30, 2026
- Last modified
- Nov 10, 2026
- NVD status
- Awaiting Analysis