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CVE-2026-27448

pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

Published: Mar 17, 2026Updated: Mar 23, 2026 Sources: CVE List NVD GHSACWE-636
NVD MITRE
5.3CVSSMEDIUM
EPSS Score
0.2%
Top 85.0%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available

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.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:LA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:LIntegrity
Low
A:NAvailability
None
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Weaknesses

CWE-636

Affected Products

pyopensslpyopenssl
Library
OSS Libraries / generic-library
pyopensslPyPIOSS Libraries
pyopensslpyca
Library
OSS Libraries / pypi
pyopenssloss-projectOSS Librariesaka pyopenssl, pyopenssl
pypipackage-ecosystemOSS Libraries
pycaoss-projectGBOSS Librariesaka pyca/cryptography, py ca, pyca

Exploitability

Official Patch Available

References

https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27
github.com
https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0
github.com
https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424
github.com
and 2 more references View all →

Timeline

Published
Mar 17, 2026
Last Updated
Mar 23, 2026

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