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

Source: https://junglewise.ai/threats/cve-2026-27448-pyopenssl-allows-tls-connection-bypass-via-unhandled-callback  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-03-18  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/pypi-pyopenssl). Vendors: [PyPI](https://junglewise.ai/threats/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

  ```sh
  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

## Related threats

- [pyOpenSSL buffer overflow in DTLS cookie generation callback](https://junglewise.ai/threats/cve-2026-27459-pyopenssl-buffer-overflow-in-dtls-cookie-generation-callback)
- [PyOpenSSL Use-After-Free vulnerability](https://junglewise.ai/threats/cve-2018-1000807-pyopenssl-use-after-free-vulnerability)
- [pyOpenSSL incorrect memory management in PKCS #12 handling](https://junglewise.ai/threats/cve-2018-1000808-pyopenssl-incorrect-memory-management-in-pkcs-12-handling)
- [PyOpenSSL Mishandles NUL Byte In Certificate Subject Alternative Name](https://junglewise.ai/threats/cve-2013-4314-pyopenssl-mishandles-nul-byte-in-certificate-subject-alternative)