CVE-2026-89665
HighCVSS 8.2Exploitation Probability (EPSS)
Low risk49th percentile - higher than 49% of all known CVEs
Summary
In the Linux kernel, the NFSv2 attribute decoder (svcxdr_decode_sattr) converts wire useconds to nanoseconds by multiplying by 1000 and storing the result in tv_nsec. On 32-bit (ILP32) architectures, an out-of-range useconds value such as 4294968 overflows and produces an incorrect tv_nsec value (e.g., 704) that passes later range checks. The vulnerability affects NFSv2 SETATTR and CREATE operations and was fixed by rejecting useconds values greater than 1000000 during decoding.
Risk Assessment
An incorrectly decoded timestamp may be written to the NFS server's filesystem, resulting in corrupted file metadata. This primarily affects NFS servers running on 32-bit architectures, where the overflow can be exploited to manipulate access and modification times.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-89665. If possible, consider running the NFS server on a 64-bit architecture where the overflow does not occur.
Other vulnerabilities in Linux kernel
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: nfsd: reject out-of-range useconds in NFSv2 SETATTR/CREATE The NFSv2 sattr decoder converts the wire useconds to nanoseconds in svcxdr_decode_sattr(): iap->ia_atime.tv_nsec = tmp2 * NSEC_PER_USEC; tmp2 is a u32 and NSEC_PER_USEC is 1000, so the product is computed in unsigned long. On ILP32 that is 32 bits, and an out-of-range useconds value such as 4294968 wraps to tv_nsec == 704. The corruption therefore happens during decode, before any proc function can inspect the value, and a later range check on tv_nsec would see an in-range result and accept it. Rejecting in the decoder yields an RPC GARBAGE_ARGS reply. NFSv2 defines no NFSERR_INVAL, so there is no NFS-level status to return for a malformed time argument, and the check cannot move to the proc function the way the v3/v4 nsec range checks do. Guard the raw useconds before the multiplication and reject values greater than 1000000. useconds == 1000000 is kept: it is the Sun convention for "set to the current server time", and the in-tree Linux NFSv2 client emits it in both the atime and the mtime field for a plain touch / utimes(file, NULL) (see encode_sattr() and xdr_encode_current_server_time() in fs/nfs/nfs2xdr.c). Rejecting 1000000 would turn that common operation into a hard decode failure for both SETATTR and CREATE. 1000000 * NSEC_PER_USEC is 10^9, which does not wrap on ILP32, so the Sun convention value passes through safely. Only genuinely out-of-range values (> 1000000) are rejected. The atime and mtime guards are therefore symmetric. The decoder only applied the Sun convention in the mtime block, which clears ATTR_ATIME_SET|ATTR_MTIME_SET when mtime useconds == 1000000. If a client puts 1000000 in the atime field but not in the mtime field, the atime block stored an out-of-range tv_nsec (10^9) and left ATTR_ATIME_SET set, so the bogus value reached the filesystem. Apply the convention in the atime block as well, clearing ATTR_ATIME_SET so the server uses its current time and ignores the value. Only ATTR_ATIME_SET is cleared there. The mtime block keeps its existing behavior, where 1000000 means "set both atime and mtime to now". [ cel: various tweaks, addenda, and clean-ups ]
Vulnerability data from NVD (NIST) · CISA KEV · EPSS