# pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

Advisory record · `GHSA-vp96-hxj8-p424`

- **Identifiers:** `GHSA-vp96-hxj8-p424` · `CVE-2026-27448` · `PYSEC-2026-2268`
- **State:** Confirmed
- **Severity:** CVSS 1.7 Low
- **Critical:** No
- **Weakness (CWE):** [CWE-636](https://cwe.mitre.org/data/definitions/636.html)
- **Tags:** [CWE-636](https://agentprime.io/advisories/tag/cwe-636.md)
- **Published:** 16 Mar 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 16 Mar 2026, 15:15 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `pyopenssl` (PyPI): affected `>=0.14.0, <26.0.0`; fixed in `26.0.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> pyOpenSSL versions 0.14.0 up to but not including 26.0.0 are affected. If a user-provided callback passed to set_tlsext_servername_callback raised an unhandled exception, the connection was accepted, which could bypass any security-sensitive checks the callback performed. Upgrade to pyOpenSSL 26.0.0, which rejects connections when the callback raises an unhandled exception.

Written 1 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 1.7 Low, CVSS 4.0: `CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0026, the 17th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:11 UTC: First seen by agentprime
- 31 Oct 2026, 14:11 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-vp96-hxj8-p424)

## Sources

- [GitHub Advisory Database: GHSA-vp96-hxj8-p424](https://github.com/advisories/GHSA-vp96-hxj8-p424)
- [OSV: GHSA-vp96-hxj8-p424](https://osv.dev/vulnerability/GHSA-vp96-hxj8-p424)
- <https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-27448>
- <https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0>
- <https://github.com/pyca/pyopenssl>
- <https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-vp96-hxj8-p424>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-vp96-hxj8-p424/>. Everything for agents: <https://agentprime.io/llms.txt>.