CVE-2026-89679
HighCVSS 7.5Exploitation Probability (EPSS)
Elevated risk51th percentile - higher than 51% of all known CVEs
Summary
In the Linux kernel, nfsd4_setattr() has a NULL pointer dereference when a SETATTR request includes delegation time attributes (FATTR4_WORD2_TIME_DELEG_ACCESS or FATTR4_WORD2_TIME_DELEG_MODIFY) and the client supplies the special stateid (all 0xFF bytes). The local variable st remains NULL and is then dereferenced, causing a kernel oops. This is remotely triggerable by any NFSv4 client without authentication.
Risk Assessment
A remote attacker can trigger a kernel oops and potentially cause a denial of service on the NFS server. No authentication or prior state is required, making it easy to exploit.
Recommendation
Update the Linux kernel to a version containing the fix that adds a NULL check before the pointer dereference. Restrict access to NFS services to trusted networks.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: nfsd: fix null dereference in nfsd4_setattr for deleg timestamp attrs When a SETATTR request includes FATTR4_WORD2_TIME_DELEG_ACCESS or FATTR4_WORD2_TIME_DELEG_MODIFY in the attribute bitmap, nfsd4_setattr() sets deleg_attrs=true and calls nfs4_preprocess_stateid_op() to validate the stateid. If the client supplies the NFSv4 "one stateid" (all-0xFF bytes), check_special_stateids() returns nfs_ok without populating the output nfs4_stid pointer, because the special-stateid path in nfs4_preprocess_stateid_op() jumps to done: with s==NULL, and the "if (s)" block that would set *cstid is skipped. The local variable `st` remains NULL. Back in nfsd4_setattr(), the if (deleg_attrs) block then unconditionally dereferences st->sc_type (at offset 4 from NULL), causing a kernel oops. This is remotely triggerable by any NFSv4 client: send COMPOUND [PUTROOTFH, SETATTR(ONE_STATEID, {bmval2=FATTR4_WORD2_TIME_DELEG_ACCESS, ...})]. No authentication, delegation, or prior state is required. Fix by adding a NULL check before the dereference. A special stateid is not a delegation stateid, so the existing nfserr_bad_stateid return value is already correct; we only need to guard the pointer dereference itself.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS