CVE-2026-53393: nfsd: reset write verifier on deferred writeback errors
In the Linux kernel, the following vulnerability has been resolved:
nfsd: reset write verifier on deferred writeback errors
nfsdvfswrite() and nfsdcommit() both call filemapcheckwberr() 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 commitresetwriteverifier() 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 commitresetwriteverifier() calls at both filemapcheckwberr() 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 Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade to a fixed release to a version that resolves this vulnerability.
Fixed in 6.6.145.2-1 - Configuration
In nfsd, ensure that both filemap_check_wb_err() call sites invoke commit_reset_write_verifier() before returning an error, so the server's write verifier (nn->writeverf) is reset when deferred writeback errors are detected.
nfsd write verifier reset on deferred writeback errors = commit_reset_write_verifier()
Event History
Frequently Asked Questions
What is the severity of CVE-2026-53393?
CVE-2026-53393 has a medium severity rating of 5.5.
How do I fix CVE-2026-53393?
To address CVE-2026-53393, update your Linux kernel to the latest version provided by your distribution.
What type of vulnerability is CVE-2026-53393?
CVE-2026-53393 is a vulnerability related to the Linux kernel's NFS server handling write verifier resets on deferred writeback errors.
What systems are affected by CVE-2026-53393?
CVE-2026-53393 affects systems running the Linux kernel with NFS server configurations.
What impact does CVE-2026-53393 have on security?
CVE-2026-53393 can potentially allow unauthorized access to data due to improper handling of write verifier resets.