CVE-2026-89678
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk29th percentile - higher than 29% of all known CVEs
Summary
In the Linux kernel, nfsd_direct_write() has a partial-write detection bug. After vfs_iocb_iter_write(), iter.count holds the residual byte count, not the original length, so the break condition is incorrect. Short writes completing between 50% and 99% of the segment are not detected, causing the next segment to be written at the wrong offset and over-reporting the byte count to the NFS client.
Risk Assessment
This can lead to data corruption on the NFS server as subsequent segments are written at incorrect offsets. The NFS client also receives incorrect byte count information, potentially causing further data integrity issues.
Recommendation
Update the Linux kernel to a version containing the fix that snapshots the segment's byte count before the write and compares host_err against that snapshot. Verify data integrity on NFS servers after the update.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix partial-write detection in nfsd_direct_write nfsd_direct_write() walks a list of write segments and, after each vfs_iocb_iter_write(), tries to detect a short write so the loop can stop before placing the next segment at a wrong file offset: host_err = vfs_iocb_iter_write(file, kiocb, &segments[i].iter); if (host_err < 0) return host_err; *cnt += host_err; if (host_err < segments[i].iter.count) break; /* partial write */ vfs_iocb_iter_write() runs the iter through ->write_iter(), which advances the iter by the number of bytes written. By the time the check runs, segments[i].iter.count is the residual, not the original request length: before write_iter: iter.count == original_len after write_iter: iter.count == original_len - host_err The condition then reduces to host_err < original_len - host_err, so the break fires only when less than half of the segment was written. Any short write completing between 50% and 99% of the segment slips through; the loop advances to the next segment with kiocb->ki_pos only bumped by the short amount, writing the next segment's payload at the wrong offset and over-reporting *cnt to the NFS client. Snapshot the segment's byte count before the write and compare host_err against that snapshot so any short write breaks the loop.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS