Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [day] [month] [year] [list]
Date: Fri, 28 Jun 2024 10:31:31 -0700
From: Alan Coopersmith <>
Subject: Fwd: [Security-announce][CVE-2024-5642] Buffer over-read in
 SSLContext.set_npn_protocols() for Python 3.9 and earlier

Note that in versions of Python that still had NPN support, whether NPN support
is built depends on which SSL library/version you build with:

-------- Forwarded Message --------
Subject: 	[Security-announce][CVE-2024-5642] Buffer over-read in 
SSLContext.set_npn_protocols() for Python 3.9 and earlier
Date: 	Thu, 27 Jun 2024 16:09:13 -0500
From: 	Seth Larson <>

There is a buffer over-read defect in CPython 3.9 and earlier due to not 
excluding an invalid value for OpenSSL's NPN APIs.

This vulnerability is of severity *LOW*.

CPython 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).

Suggested mitigation is one of the following:

* Upgrade to Python 3.10 or later where NPN isn't supported
* Avoid using NPN via SSLContext.set_npn_protocols()
* Avoid providing an empty list as a parameter to SSLContext.set_npn_protocols()
View attachment "Attached Message Part" of type "text/plain" (292 bytes)

Powered by blists - more mailing lists

Please check out the Open Source Software Security Wiki, which is counterpart to this mailing list.

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.