CVE-2026-19445
Use-after-free of a server-side SSLContext when sni_callback switches contexts
- State
- Published
- Severity
- 9.2 Critical
- Published
- Sep 30, 2026
- Updated
- Oct 3, 2026
- Reserved
- Aug 10, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 9.2 Critical | 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 | PSF |
Weaknesses
Affected Products
| Product | Versions |
|---|---|
CPythonPython Software Foundation |
|
References
- https://github.com/python/cpython/pull/158504patch
- https://mail.python.org/archives/list/security-announce@python.org/thread/QMQIUQB6WGGC3MI7I3WKQXOYOBDSPPS3/vendor-advisory
- https://github.com/python/cpython/issues/156293issue-tracking
- https://github.com/python/cpython/commit/34a53dce8174da2fceb12fe084a4def02a10053dpatch
- https://github.com/python/cpython/commit/46133cd57d309652139ada74014aca7665ac552bpatch
- https://github.com/python/cpython/commit/63fab143d94cafae71850831acfb52041ba44af7patch
- https://github.com/python/cpython/commit/cd7e51e7d4563866fbaa1e2521ae69b45daf3698patch
- https://github.com/python/cpython/commit/d8717ed01717a9641686e6e6f83f0ab8af235e2cpatch
- https://github.com/python/cpython/commit/b12968cefe69ca1dcb8606c832ff73ee7dbf4ba8patch
- https://github.com/python/cpython/commit/ec44b5a3258cbda947d5e07242ee562ed05ef24bpatch
- http://www.openwall.com/lists/oss-security/2026/09/30/17
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