EUVD-2026-31254
GHSA-fqrg-fvv5-42g2
Severity by source
AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:N/A:H
Lifecycle Timeline
4DescriptionCVE.org
When a fusefs file system implements extended attributes, the kernel may send a FUSE_LISTXATTR message to the userspace daemon to retrieve the list of extended attributes for a given file. The FUSE protocol requires the daemon to return a packed list of NUL-terminated strings. The fusefs kernel module calls strlen() on this daemon-supplied buffer without first verifying that the entire list is NUL-terminated.
If a malicious daemon sends a non-NUL-terminated list, the fusefs kernel module may read beyond the end of one heap-allocated buffer and potentially write beyond the end of a second buffer. A malicious daemon could disclose up to 253 bytes of kernel heap memory, or it could inject up to 250 attacker-controlled bytes into unallocated kernel heap space.
AnalysisAI
FreeBSD's fusefs kernel module mishandles extended attribute list responses from FUSE userspace daemons by calling strlen() on daemon-supplied buffers without first verifying NUL-termination, enabling a malicious daemon operator to read up to 253 bytes of kernel heap memory or inject up to 250 attacker-controlled bytes into unallocated kernel heap space. Affected releases are FreeBSD 14.3-RELEASE prior to p14, 14.4-RELEASE prior to p5, and 15.0-RELEASE prior to p9 per FreeBSD-SA-26:20.fusefs and EUVD-2026-31254. No public exploit code exists and EPSS sits at 0.02% (5th percentile), though the heap write primitive carries local privilege escalation potential beyond what the CVSS integrity score reflects.
Technical ContextAI
The vulnerable component is FreeBSD's fusefs kernel module, which implements the in-kernel side of the FUSE (Filesystem in Userspace) protocol, bridging userspace daemon processes and the kernel VFS layer. The CWE-122 (Heap-based Buffer Overflow) root cause is a missing input validation step: when the kernel issues a FUSE_LISTXATTR request and receives the daemon's packed list of NUL-terminated attribute name strings, it passes that response buffer directly to strlen() without confirming the entire payload is properly NUL-terminated. A daemon response that omits the final NUL causes strlen() to read past the end of the heap-allocated receive buffer (over-read of up to 253 bytes), and the resulting miscalculated length can additionally cause a write of up to 250 attacker-controlled bytes into an adjacent unallocated heap region. The CPE cpe:2.3:a:freebsd:freebsd:*:*:*:*:*:*:*:* covers the FreeBSD base system; only deployments with fusefs loaded and FUSE filesystems mounted are exposed to this code path.
RemediationAI
Apply vendor-released patches by upgrading to FreeBSD 14.4-RELEASE-p5, FreeBSD 14.3-RELEASE-p14, or FreeBSD 15.0-RELEASE-p9 as appropriate, per the official advisory at https://security.freebsd.org/advisories/FreeBSD-SA-26:20.fusefs.asc. Until patching is feasible, a targeted compensating control is to disable user-mountable FUSE filesystems by setting the sysctl vfs.usermount=0 (and persisting it in /etc/sysctl.conf), which ensures only root-operated FUSE daemons - which imply full system trust - can trigger the vulnerable code path; the trade-off is that non-root users lose the ability to mount any filesystem type, including legitimate FUSE tools such as sshfs or gocryptfs. Alternatively, unloading or blacklisting the fusefs kernel module entirely eliminates exposure with the trade-off of disabling all FUSE functionality system-wide. No partial workaround that preserves untrusted-user FUSE access while mitigating the strlen over-read is documented in available references.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
Leaving vuln.today