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Date: Wed, 27 Mar 2024 07:58:12 +0100 (CET)
From: Daniel Stenberg <>
To: curl security announcements -- curl users <>,, libcurl hacking <>,
Subject: [SECURITY ADVISORY] curl: CVE-2024-2466: TLS certificate check bypass
 with mbedTLS

TLS certificate check bypass with mbedTLS

Project curl Security Advisory, March 27th 2024 -


libcurl did not check the server certificate of TLS connections done to a host
specified as an IP address, when built to use mbedTLS.

libcurl would wrongly avoid using the set hostname function when the specified
hostname was given as an IP address, therefore completely skipping the
certificate check. This affects all uses of TLS protocols (HTTPS, FTPS, IMAPS,
POPS3, SMTPS, etc).


Since the SNI field is not set when using a hostname set as an IP address,
many requests will fail to communicate with the correct endpoint or get the
correct data. Somewhat lessening the possible impact.

Not all versions of mbedTLS supports server certificate checks for IP
addresses, so when this issue is fixed all attempts to connect directly to an
IP address over TLS might fail.

This vulnerability is similar to a past curl vulnerability identified as

This flaw also affects the curl command line tool.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2024-2466 to this issue.

CWE-297: Improper Validation of Certificate with Host Mismatch

Severity: Medium


This flaw is relevant for curl and libcurl built to use mbedTLS.

- Affected versions: curl 8.5.0 to and including 8.6.0
- Not affected versions: curl < 8.5.0 and >= 8.7.0
- Introduced-in:

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


- Fixed-in:


We suggest you take one of the following actions immediately, in order of

  A - Upgrade curl and libcurl to version 8.7.0

  B - Apply the patch to your version and rebuild

  C - Build your libcurl with another TLS backend


This issue was reported to the curl project on March 14, 2024. We contacted
distros@...nwall on March 19, 2024.

curl 8.7.0 was released on March 27 2024 around 07:00 UTC, coordinated with
the publication of this advisory.


- Reported-by: Frank Yueh
- Patched-by: Stefan Eissing

Thanks a lot!



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