CVE-2026-27448: pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

CVE-2026-27448 · Severity: medium · CVSS 4 · Published 2026-03-18

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.

Technologies: pyopenssl (PyPI). Vendors: PyPI.

Quick answers

Is CVE-2026-27448 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-27448 being exploited in the wild.
How severe is CVE-2026-27448?
Medium severity, with a CVSS score of 4, published 18 March 2026.
Which products and versions are affected?
pyopenssl (PyPI) ECOSYSTEM:introduced=0.14,fixed=26.0.0, ECOSYSTEM:introduced=0.14.0,fixed=26.0.0.
Is there a fix for CVE-2026-27448?
Yes. pyopenssl (PyPI): upgrade to 26.0.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2026-27448?
Check whether you run pyopenssl (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • pyopenssl (PyPI): upgrade to 26.0.0 or later
    pip install "pyopenssl>=26.0.0"

Affected products

  • pyopenssl (PyPI) ECOSYSTEM:introduced=0.14,fixed=26.0.0, ECOSYSTEM:introduced=0.14.0,fixed=26.0.0

Identifiers

  • CVE-2026-27448
  • GHSA-vp96-hxj8-p424
  • PYSEC-2026-2268

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