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.
CVSS Details
- CVSS 4.0 Base Score: 9.2 (CRITICAL)
- CVSS 4.0 Vector: (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)
Covered by Rapid7
| Product | Vendor Advisory | Solution File | Added | Published |
|---|---|---|---|---|
| Alpine Linux | — | Upgrade python3 | Oct 2, 2026 | Sep 30, 2026 |
| Redhat_linux | — | Upgrade python3.12-tkinterUpgrade python3.12-libsUpgrade python3.12Upgrade python3.12-debugUpgrade python3.12-debugsourceUpgrade python3.12-debuginfoUpgrade python3.12-rpm-macrosUpgrade python3.12-develUpgrade python3.12-idleUpgrade python3.12-testNo solution exists | Oct 7, 2026 | Sep 30, 2026 |
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