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CVE-2026-89704

HIGHCVSS 7.5/10EPSS 0.44%

Last modified

CVE-2026-89704 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. In the Linux kernel, the following vulnerability has been resolved: nfsd: sample writeback error cursor before async COPY loop _nfsd_copy_file_range() samples dst->f_wb_err into "since" after the copy loop, then uses it to detect writeback errors via filemap_check_wb_err() once vfs_fsync_range() returns. Because the nfsd_file cache reuses a single struct file across requests targeting the same inode, a concurrent COMMIT or stable WRITE on dst advances dst->f_wb_err to the current mapping->wb_err via file_check_and_advance_wb_err() during its own vfs_fsync_range(). If that advancement lands between the writeback error appearing in mapping->wb_err and the COPY worker sampling "since", the worker captures the already-advanced cursor, errseq_check() sees cur == since and returns zero, and NFSD4_COPY_F_COMMITTED is set even though writeback failed. EPSS estimates a 0.44% chance of exploitation in the next 30 days.

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: sample writeback error cursor before async COPY loop _nfsd_copy_file_range() samples dst->f_wb_err into "since" after the copy loop, then uses it to detect writeback errors via filemap_check_wb_err() once vfs_fsync_range() returns. Because the nfsd_file cache reuses a single struct file across requests targeting the same inode, a concurrent COMMIT or stable WRITE on dst advances dst->f_wb_err to the current mapping->wb_err via file_check_and_advance_wb_err() during its own vfs_fsync_range(). If that advancement lands between the writeback error appearing in mapping->wb_err and the COPY worker sampling "since", the worker captures the already-advanced cursor, errseq_check() sees cur == since and returns zero, and NFSD4_COPY_F_COMMITTED is set even though writeback failed. CB_OFFLOAD then encodes wr_stable_how = FILE_SYNC4, the client treats the copied data as durable, and the failure becomes silent data loss. Sample since once at the start of the function. The cursor then reflects state in effect before this COPY issues any writes, and filemap_check_wb_err() detects any error that occurs during the copy regardless of which thread first observes it. This matches the pattern used by nfsd_vfs_write() and nfsd4_clone_file_range().

Metrics

CVSS 3.1
7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS Probability
0.44%

37.5th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

VendorProductVersions
LinuxLinux>= f14816f2f928c560d28ba344af689f56efcd6f55, < 435e4246c7dfff2fbd76dfdbf91975d5d9f788c9; >= 3145fe0ebb16e1715ad541a301bc6675c8375fcd, < 9f539a1c0791f907eb4e6d04b43178d9962e2def; >= 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb, < 4728504c021656128a07f4693af80ed4a5fcc863; >= 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb, < 322422d66d1a04434a0dcc0c9d3a4c4b3f225117; >= 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb, < 52b2db7a72e19ac2686fa4b2a52406661e7bf9e2; >= 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb, < 8277d4a11ae2cb5495842be558fd946032c24363; >= 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb, < a1cbafe756cd5e6ab0e099062f37da7a5b081169; >= 555dbf1a9aac6d3150c8b52fa35f768a692f4eeb, < 20a67a7d18221af736f124770c2c5e859b479046; >= 5.10.124, < 5.10.270; >= 5.15.49, < 5.15.221
LinuxLinux5.17

References

Timeline

Published
Last Modified
Status
Received

Frequently Asked Questions

What is CVE-2026-89704?
In the Linux kernel, the following vulnerability has been resolved: nfsd: sample writeback error cursor before async COPY loop _nfsd_copy_file_range() samples dst->f_wb_err into "since" after the copy loop, then uses it to detect writeback errors via filemap_check_wb_err() once vfs_fsync_range() returns. Because the nfsd_file cache reuses a single struct file across requests targeting the same inode, a concurrent COMMIT or stable WRITE on dst advances dst->f_wb_err to the current mapping->wb_err via file_check_and_advance_wb_err() during its own vfs_fsync_range(). If that advancement lands between the writeback error appearing in mapping->wb_err and the COPY worker sampling "since", the worker captures the already-advanced cursor, errseq_check() sees cur == since and returns zero, and NFSD4_COPY_F_COMMITTED is set even though writeback failed. CB_OFFLOAD then encodes wr_stable_how = FILE_SYNC4, the client treats the copied data as durable, and the failure becomes silent data loss. Sample since once at the start of the function. The cursor then reflects state in effect before this COPY issues any writes, and filemap_check_wb_err() detects any error that occurs during the copy regardless of which thread first observes it. This matches the pattern used by nfsd_vfs_write() and nfsd4_clone_file_range().
How severe is CVE-2026-89704?
CVE-2026-89704 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 0.44% probability of exploitation in the next 30 days.
How do I fix CVE-2026-89704?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST