FreeBSD Security Advisory FreeBSD-SA-25:06.xz
2 July, 2025 by security-advisories@freebsd.org | freebsd
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FreeBSD-SA-25:06.xz Security Advisory
The FreeBSD Project
Topic: Use-after-free in multi-threaded xz decoder
Category: contrib
Module: xz
Announced: 2025-07-02
Affects: FreeBSD 13.5 and FreeBSD 14.2
Corrected: 2025-05-07 21:26:00 UTC (stable/14, 14.2-STABLE)
2025-07-02 18:28:13 UTC (releng/14.2, 14.2-RELEASE-p4)
2025-05-07 21:25:59 UTC (stable/13, 13.4-STABLE)
2025-07-02 18:28:32 UTC (releng/13.5, 13.5-RELEASE-p2)
CVE Name: CVE-2025-31115
For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.
I. Background
XZ Utils is a set of free software command-line lossless data compressors,
including the programs lzma and xz.
II. Problem Description
A worker thread could free its input buffer after decoding, while the
main thread might still be writing to it. This leads to an use-after-free
condition on heap memory.
III. Impact
An attacker may use specifically crafted .xz file to cause multi-threaded
xz decoder to crash, or potentially run arbitrary code under the credential
the decoder was executed.
IV. Workaround
No workaround is available, but systems where xz decoding was not used in
multi-threaded mode are not affected.
V. Solution
Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date.
Unless the decoder is running as a daemon, no reboot is required.
Perform one of the following:
1) To update your vulnerable system via a binary patch:
Systems running a RELEASE version of FreeBSD on the amd64 or arm64 platforms,
or the i386 platform on FreeBSD 13, can be updated via the freebsd-update(8)
utility:
# freebsd-update fetch
# freebsd-update install
# shutdown -r +10min "Rebooting for a security update"
2) To update your vulnerable system via a source code patch:
The following patches have been verified to apply to the applicable
FreeBSD release branches.
a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.
# fetch https://security.FreeBSD.org/patches/SA-25:06/xz.patch
# fetch https://security.FreeBSD.org/patches/SA-25:06/xz.patch.asc
# gpg --verify xz.patch.asc
b) Apply the patch. Execute the following commands as root:
# cd /usr/src
# patch < /path/to/patch
c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.
Restart all daemons that use the liblzma library, or reboot the system.
VI. Correction details
This issue is corrected as of the corresponding Git commit hash in the
following stable and release branches:
Branch/path Hash Revision
- -------------------------------------------------------------------------
stable/14/ 5cf27a49a2de stable/14-n271423
releng/14.2/ 49b07b94662b releng/14.2-n269529
stable/13/ 346bb5d3fe19 stable/13-n259281
releng/13.5/ 95e9c54b3961 releng/13.5-n259171
- -------------------------------------------------------------------------
Run the following command to see which files were modified by a
particular commit:
# git show --stat <commit hash>
Or visit the following URL, replacing NNNNNN with the hash:
<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>
To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:
# git rev-list --count --first-parent HEAD
VII. References
<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-31115>
<URL:https://tukaani.org/xz/threaded-decoder-early-free.html>
The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-25:06.xz.asc>
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