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Message-ID: <p1728624-2s9n-4689-8128-387qpn026q5o@unkk.fr>
Date: Wed, 7 Jan 2026 08:09:40 +0100 (CET)
From: Daniel Stenberg <daniel@...x.se>
To: curl security announcements -- curl users <curl-users@...ts.haxx.se>,
curl-announce@...ts.haxx.se, libcurl hacking <curl-library@...ts.haxx.se>,
oss-security@...ts.openwall.com
Subject: [ADVISORY] curl CVE-2025-15079: libssh global knownhost override
libssh global knownhost override
================================
Project curl Security Advisory, January 7 2026 -
[Permalink](https://curl.se/docs/CVE-2025-15079.html)
VULNERABILITY
-------------
When doing SSH-based transfers using either SCP or SFTP, and setting the
knownhosts file, libcurl could still mistakenly accept connecting to hosts
*not present* in the specified file if they were added as recognized in the
libssh *global* knownhosts file.
INFO
----
This flaw only exists when libcurl is built to use the libssh backend, not the
libssh2 based one. This problem happened because libssh has a somewhat
surprising API choice where they fall back to a built-in *global* knownhosts
file if the host was not found in the specified one. The global file that was
used as a fallback gets its set path at build time.
The fix now makes libcurl set *both* knownhost files to the same path.
The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2025-15079 to this issue.
CWE-297: Improper Validation of Certificate with Host Mismatch
Severity: Low
AFFECTED VERSIONS
-----------------
- Affected versions: curl 7.58.0 to and including 8.17.0
- Not affected versions: curl < 7.58.0 and >= 8.18.0
- Introduced-in: https://github.com/curl/curl/commit/c92d2e14cfb0db662f958effd2ac86f99
libcurl is used by many applications, but not always advertised as such!
This bug is not considered a *C mistake*. It is not likely to have been
avoided had we not been using C.
This flaw **also** affects the curl command line tool.
SOLUTION
------------
Starting in curl 8.18.0, this mistake is fixed.
- Fixed-in: https://github.com/curl/curl/commit/adca486c125d9a6d9565b9607a19dce803
RECOMMENDATIONS
--------------
A - Upgrade curl to version 8.18.0
B - Build curl with the libssh2 backend
C - Avoid using SFTP or SCP
TIMELINE
--------
This issue was reported to the curl project on December 24, 2025. We contacted
distros@...nwall on December 30, 2025.
curl 8.18.0 was released on January 7 2026 around 07:00 UTC, coordinated with
the publication of this advisory.
The curl security team is not aware of any active exploits using this
vulnerability.
CREDITS
-------
- Reported-by: Harry Sintonen
- Patched-by: Daniel Stenberg
Thanks a lot!
--
/ daniel.haxx.se || https://rock-solid.curl.dev
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