CVE-2026-27448
pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback
5.3
MEDIUM
CVSS 3.1
EPSS 0.04%
Description
pyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 0.14.0 and prior to version 26.0.0, 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. Starting in version 26.0.0, unhandled exceptions now result in rejecting the connection.
How to fix CVE-2026-27448
To remediate CVE-2026-27448, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 26.0.0 or later
Is CVE-2026-27448 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0
- >= 0.14.0, < 26.0.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U |
| osv | CVSS 3.1 | MEDIUM5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N |