CVE-2026-115557
CriticalCVSS 9.4Summary
Python has added a denylist for known compromised certificates to the "ssl" module to ensure user safety even without certificate revocation configured. Known compromised certificates will automatically be rejected regardless of the SSLContext policy configuration.
Risk Assessment
Without this fix, applications could accept connections using compromised certificates, enabling man-in-the-middle attacks. Applying the fix mitigates this risk regardless of configuration.
Recommendation
Update the Python interpreter to a version containing this fix. Verify that applications do not rely on accepting certificates now present on the denylist.
Other vulnerabilities in Python ssl module
See all- CVE-2026-19445Critical
A remote, unauthenticated TLS client can crash a server or trigger a use-after-free 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.
- CVE-2026-19553High
ssl.SSLContext.wrap_bio() didn't require the server_hostname argument to not be None if ssl.SSLContext.check_hostname was set. Due to a missing parameter check in SSLObject, if the server_hostname argument isn't supplied then hostname verification would be silently skipped. This defect could lead to programs where certificate hostname verification *appeared* to be succeeding with SSLContext.check_hostname = True and no ValueError being raised due to misconfiguration.
Original NVD description (English source)
Python has added a denylist for known compromised certificates to the "ssl" module to ensure user safety even without certificate revocation configured. Known compromised certificates will automatically be rejected regardless of the SSLContext policy configuration.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS