---
id: CVE-2024-5642
title: >-
  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
summary: >-
  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…
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:L'
published: '2024-06-27'
updated: '2026-07-31'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2024-5642'
references:
  - url: 'http://www.openwall.com/lists/oss-security/2024/06/28/4'
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/39258d3595300bc7b952854c915f63ae2d4b9c3e
    label: cna@python.org
  - url: >-
      https://github.com/python/cpython/commit/a2cdbb6e8188ba9ba8b356b28d91bff60e86fe31
    label: cna@python.org
  - url: 'https://github.com/python/cpython/issues/121227'
    label: cna@python.org
  - url: 'https://github.com/python/cpython/pull/23014'
    label: cna@python.org
  - url: 'https://jbp.io/2024/06/27/cve-2024-5535-openssl-memory-safety.html'
    label: cna@python.org
  - url: >-
      https://mail.python.org/archives/list/security-announce@python.org/thread/PLP2JI3PJY33YG6P5BZYSSNU66HASXBQ/
    label: cna@python.org
  - url: 'https://security.netapp.com/advisory/ntap-20240726-0005/'
    label: cna@python.org
  - url: 'http://www.openwall.com/lists/oss-security/2024/06/28/4'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://github.com/python/cpython/commit/39258d3595300bc7b952854c915f63ae2d4b9c3e
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://github.com/python/cpython/issues/121227'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://github.com/python/cpython/pull/23014'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://jbp.io/2024/06/27/cve-2024-5535-openssl-memory-safety.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://mail.python.org/archives/list/security-announce@python.org/thread/PLP2JI3PJY33YG6P5BZYSSNU66HASXBQ/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://security.netapp.com/advisory/ntap-20240726-0005/'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00744
epssPercentile: 0.53311
ingestedAt: '2026-07-31T15:59:52.003Z'
---

## Overview

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).

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.