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Unhandled exceptions in set_tlsext_servername_callback callbacks did not cancel connections

Low
alex published GHSA-vp96-hxj8-p424 Mar 15, 2026

Package

pip pyopenssl (pip)

Affected versions

>=0.14

Patched versions

>=26.0.0

Description

If a user provided callback to set_tlsext_servername_callback raised an unhandled exception, this would result in a connection being accepted. If a user was relying on this callback for any security-sensitive behavior, this could allow bypassing it.

Unhandled exceptions now result in rejecting the connection.

Credit to Leury Castillo for reporting this issue.

Severity

Low

CVE ID

CVE-2026-27448

Weaknesses

No CWEs