Affects CPython's stdlib TLS handling—widely used runtime. Remote unauthenticated clients can crash or trigger use-after-free; could disrupt many Python servers and services.
CVE-2026-19445
CPython SSLContext SNI callback use-after-free can crash or corrupt servers.
Is CVE-2026-19445 being exploited?
Not confirmed. CVE-2026-19445 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked.
How severe is CVE-2026-19445?
CVE-2026-19445 is rated Critical with a CVSS score of 9.2. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-19445?
Yes. A fix has been recorded for CVE-2026-19445. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-19445 affect?
CVE-2026-19445 affects CPython ssl module, Python servers using sni_callback, Apps creating per-connection SSLContext. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-19445?
Upgrade CPython to patched release; ensure SSLContext objects with sni_callback are kept alive.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Remote unauthenticated TLS client can crash servers or trigger use-after-free by swapping SSLContext via sni_callback, enabling DoS or potential RCE.
Immediate action required
- affected< 3.12.15
- affected>= 3.13.0 and < 3.13.16
- affected>= 3.14.0 and < 3.14.8
- affected>= 3.15.0a1 and < 3.15.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.