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Date: Wed, 31 Jan 2024 08:12:18 +0100 (CET)
From: Daniel Stenberg <>
To: curl security announcements -- curl users <>,, libcurl hacking <>,
Subject: [SECURITY ADVISORY] curl: CVE-2024-0853 : OCSP verification bypass
 with TLS session reuse

OCSP verification bypass with TLS session reuse

Project curl Security Advisory, January 31 2024 -


curl inadvertently kept the SSL session ID for connections in its cache even
when the verify status (*OCSP stapling*) test failed. A subsequent transfer to
the same hostname could then succeed if the session ID cache was still fresh,
which then skipped the verify status check.


This issue is limited to curl built to use OpenSSL and when using TLS 1.2 only
and not TLS 1.3.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2024-0853 to this issue.

CWE-299: Improper Check for Certificate Revocation

Severity: Low


- Affected versions: curl 8.5.0 to and including 8.5.0
- Not affected versions: curl < 8.5.0 and >= 8.6.0
- Introduced-in:

libcurl is used by many applications, but not always advertised as such!

This flaw is also accessible using the curl command line tool.


If verify status fails, make sure the session id is not cached.

- Fixed-in:


  A - Upgrade curl to version 8.6.0

  B - Apply the patch to your local version

  C - Do not use curl built to use OpenSSL

  D - Do not allow TLS 1.2 for your transfers


This issue was reported to the curl project on December 29, 2023. We contacted
distros@...nwall on January 24, 2024.

curl 8.6.0 was released on January 31 2024 around 07:00 UTC, coordinated with
the publication of this advisory.


- Reported-by: Hiroki Kurosawa
- Patched-by: Daniel Stenberg

Thanks a lot!


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