CVE-2026-89666
Low risk· EPSS 6%Exploitation Probability (EPSS)
Low risk6th percentile - higher than 6% of all known CVEs
Summary
In the Linux kernel's nfsd module, a client could send an NFSv3 SETATTR, CREATE, MKDIR, SYMLINK or MKNOD request with an out-of-range nseconds field for atime/mtime (tv_nsec >= NSEC_PER_SEC). The value passed protocol-level validation but was not normalized, leading to on-disk metadata corruption on ext4 and XFS filesystems (incorrect seconds and year). The fix rejects such requests with NFS3ERR_INVAL before any changes are made.
Risk Assessment
The vulnerability allows a remote NFS client to corrupt file and directory timestamps on the server, potentially causing incorrect dates, backup, audit and data integrity issues. For object creation operations (CREATE, MKDIR, SYMLINK, MKNOD), the request could also leave a new object in the filesystem despite reporting a failure.
Recommendation
Update the Linux kernel to a version containing the fix for CVE-2026-89666. Until patched, consider restricting NFSv3 service access to trusted clients only.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: nfsd: reject out-of-range nseconds in NFSv3 SETATTR and create ops A client can send an NFSv3 SETATTR, CREATE, MKDIR, SYMLINK or MKNOD carrying an atime or mtime whose nseconds field is out of range. The value is well-formed on the wire and decodes cleanly into a valid uint32, but it is not a valid timespec64: tv_nsec must be less than NSEC_PER_SEC. Nothing in the setattr path clamps it. notify_change() runs the time through timestamp_truncate(), which does not reduce tv_nsec below NSEC_PER_SEC when the filesystem supports nanosecond granularity (s_time_gran == 1), and the inode atime/mtime setters store it verbatim (only ctime is normalized, via inode_set_ctime_to_ts()). The un-normalized value then corrupts on-disk metadata: ext4's ext4_encode_extra_time() shifts tv_nsec left by EXT4_EPOCH_BITS, which overflows the 32-bit extra field and clobbers the seconds-epoch bits, so the stored seconds (and thus the year) are wrong on read-back. XFS with bigtime mis-stores the timestamp for the same reason. Validate the client-supplied atime/mtime in the proc handlers and return NFS3ERR_INVAL before anything is changed. RFC 1813 lists NFS3ERR_INVAL for SETATTR and describes it as the error for a value the server 'can not store ... in its own representation'; the client maps it to EINVAL. Checking in the proc handlers, rather than in nfsd_setattr(), keeps the rejection in front of object creation. The create operations create the object before nfsd_create_setattr() runs, so a late failure would leave the new object behind and turn a non-idempotent request into a namespace change that reports failure. The check is therefore done up front, for the create operations before the object is created. tv_nsec is a long, so the comparison casts it to unsigned long (the same width) rather than to u32, matching timespec64_valid(). A u32 cast would truncate on 64-bit; the unsigned long cast also rejects a value that became negative when an out-of-range u32 wire nseconds was assigned to a 32-bit long. Only client-supplied times are checked: SET_TO_SERVER_TIME requests carry no client value. The sattrguard3 ctime is deliberately left alone: an out-of-range guard simply never matches the object's ctime and yields NFS3ERR_NOT_SYNC via the existing guardtime comparison, which is the protocol-correct outcome rather than rejecting the request.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS