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Message-ID: <rq2n27r2-25s1-p567-ps6q-5396rn1p50q8@unkk.fr>
Date: Wed, 11 Mar 2026 07:54:50 +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-2026-3805: use after free in SMB connection
reuse
use after free in SMB connection reuse
======================================
Project curl Security Advisory, March 11th 2026
[Permalink](https://curl.se/docs/CVE-2026-3805.html)
VULNERABILITY
-------------
When doing a second SMB request to the same host again, curl would wrongly use
a data pointer pointing into already freed memory.
INFO
----
When the bad code hits, curl first makes a `strlen()` on the (freed) memory
pointer, then checks that the size is less than or equal than 1024 for it to
do something.
Then it copies that string to the the outgoing package which then potentially
could leak sensitive data if the application happened to put it there in the
mean time since the previous transfer.
This seems extremely hard for an attacker to willingly abuse or to massage the
application into leaking specific information. It also seems highly unlikely
that any application ever did this sequence without getting a crash or another
issue that would indicate there is a problem in curl. The risk here is
therefore minimal.
The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2026-3805 to this issue.
CWE-416: Use After Free
Severity: Medium
AFFECTED VERSIONS
-----------------
- Affected versions: curl 8.13.0 to and including 8.18.0
- Not affected versions: curl < 8.13.0 and >= 8.19.0
- Introduced-in: https://github.com/curl/curl/commit/f4831daa9b2a97e8a29
libcurl is used by many applications, but not always advertised as such!
This bug is considered a *C mistake*. It is likely to have been avoided had we
not been using C.
This flaw also affects the curl command line tool.
SOLUTION
--------
curl 8.19.0 fixes this flaw
- Fixed-in: https://github.com/curl/curl/commit/e090be9f73a7a71459ef678c
RECOMMENDATIONS
---------------
We suggest you take one of the following actions immediately, in order of
preference:
A - Upgrade to curl and libcurl 8.19.0
B - Apply the patch and rebuild libcurl
C - Do not use SMB transfers
TIMELINE
---------
It was reported to the curl project on March 8th 2026. We contacted
distros@...nwall on March 8.
libcurl 8.19.0 was released on March 11th 2026, coordinated with the
publication of this advisory.
CREDITS
-------
- Reported-by: Daniel Wade
- Patched-by: Stefan Eissing
Thanks a lot!
--
/ daniel.haxx.se || https://rock-solid.curl.dev
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