pyca/pyopenssl · Security
pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback
- GHSA ID
- GHSA-vp96-hxj8-p424
- CVE ID
- CVE-2026-27448
- Severity
- low
- Published
- Updated
- CVSS v4
- 1.7 · 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
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.
CWEs
- CWE-636 · Not Failing Securely ('Failing Open')
References
- https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424 ↗
- https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0 ↗
- https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27 ↗
- https://nvd.nist.gov/vuln/detail/CVE-2026-27448 ↗
- https://github.com/advisories/GHSA-vp96-hxj8-p424 ↗