---
id: CVE-2026-27448
aliases:
  - GHSA-vp96-hxj8-p424
  - PYSEC-2026-2268
title: >-
  pyOpenSSL allows TLS connection bypass via unhandled callback exception in
  set_tlsext_servername_callback
summary: >-
  pyOpenSSL allows TLS connection bypass via unhandled callback exception in
  set_tlsext_servername_callback
severity: low
vendor: pyopenssl
product: pyopenssl
ecosystem: pip
affected:
  - 'pyopenssl >= 0.14.0, < 26.0.0'
patched:
  - pyopenssl 26.0.0
published: '2026-03-16'
updated: '2026-09-10'
sourceUpdated: '2026-09-10T03:51:00.753013360Z'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-vp96-hxj8-p424'
references:
  - url: 'https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-27448'
  - url: >-
      https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0
  - url: 'https://github.com/pyca/pyopenssl'
  - url: >-
      https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27
tags:
  - osv
  - pip
epss: 0.00392
epssPercentile: 0.30449
ingestedAt: '2026-07-13T18:58:03.715Z'
---

## Overview

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.

## Affected packages

- `pyopenssl >= 0.14.0, < 26.0.0`

## Remediation

Upgrade to a patched release:

- `pyopenssl 26.0.0`