CVE-2026-19445
Use-after-free of a server-side SSLContext when sni_callback switches contexts
CRITICAL 9.2EPSS 0.4%
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.
- Affected
- Python Software Foundation · CPython
- CVSS v4.0 PYTHON
- 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/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 - EPSS
- 0.43% chance of exploitation in the next 30 days, 36th percentile
- Published
- 2026-09-30
- Updated
- 2026-10-03
Proof-of-concept exploits (1)
- abraxas/cve-2026-19445-sni-uaf0★ · 2026-10-07