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

5.3MEDIUM

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.

No summary for this CVE yet.

CVSS Vector Breakdown

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

pyopenssl

oss-project

pyopensslLibrary

OSS Libraries / generic-library

package-ecosystem

oss-project·GBaka py ca, pyca/cryptography

pyopensslLibrary

OSS Libraries / pypi

Exploitability

Official Patch Available

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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 →

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