CVE-2026-31402

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix heap overflow in NFSv4.0 LOCK replay cache

The NFSv4.0 replay cache uses a fixed 112-byte inline buffer

(rp_ibuf[NFSD4_REPLAY_ISIZE]) to store encoded operation responses.

This size was calculated based on OPEN responses and does not account

for LOCK denied responses, which include the conflicting lock owner as

a variable-length field up to 1024 bytes (NFS4_OPAQUE_LIMIT).

When a LOCK operation is denied due to a conflict with an existing lock

that has a large owner, nfsd4_encode_operation() copies the full encoded

response into the undersized replay buffer via read_bytes_from_xdr_buf()

with no bounds check. This results in a slab-out-of-bounds write of up

to 944 bytes past the end of the buffer, corrupting adjacent heap memory.

This can be triggered remotely by an unauthenticated attacker with two

cooperating NFSv4.0 clients: one sets a lock with a large owner string,

then the other requests a conflicting

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References