CVE-2026-53393: nfsd: reset write verifier on deferred writeback errors

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-19 · updated 2026-08-17

Description

In the Linux kernel, the following vulnerability has been resolved: nfsd: reset write verifier on deferred writeback errors nfsd_vfs_write() and nfsd_commit() both call filemap_check_wb_err() to detect deferred writeback errors, but neither rotates the server's write verifier (nn->writeverf) when this check fails. Every other durable-storage-failure path in these functions calls commit_reset_write_verifier() before returning an error. The missing rotation means clients holding UNSTABLE write data under the current verifier will COMMIT, receive the unchanged verifier back, and conclude their data is durable — silently dropping data that failed writeback. This violates the UNSTABLE+COMMIT durability contract (RFC 1813 §3.3.7, RFC 8881 §18.32). Add commit_reset_write_verifier() calls at both filemap_check_wb_err() error sites, matching the pattern used by adjacent error paths in the same functions. The helper already filters -EAGAIN and -ESTALE internally, so the calls are unconditionally safe.

Affected products

Linux kernel: from 5.10.124 before 5.10.261; from 5.15.49 before 5.15.212; from 5.17 before 6.1.178; from 6.2 before 6.6.145; from 6.7 before 6.12.95; from 6.13 before 6.18.38 — fixed in 5.10.261, 5.15.212, 6.1.178, 6.12.95, 6.18.38, 6.6.145

How to fix

Upgrade to a fixed version: Linux kernel 5.10.261, 5.15.212, 6.1.178, 6.12.95. Check the vendor advisory for mitigations.

References

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