CVE-2026-31402: Linux Kernel buffer overflow (CVSS 9.8)

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 lock to provoke the denial. We could fix this by increasing NFSD4_REPLAY_ISIZE to allow for a full opaque, but that would increase the size of every stateowner, when most lockowners are not that large. Instead, fix this by checking the encoded response length against NFSD4_REPLAY_ISIZE before copying into the replay buffer. If the response is too large, set rp_buflen to 0 to skip caching the replay payload. The status is still cached, and the client already received the correct response on the original request.

CVSS 3.1 breakdown

Attack vectorNetwork

Attack complexityLow

Privileges requiredNone

User interactionNone

ScopeUnchanged

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

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

Affected products

Linux Kernel≥ 2.6.12.1 < 5.10.253 · ≥ 5.11 < 6.1.167 · ≥ 6.13 < 6.18.20 · ≥ 6.19 < 6.19.10

Remediation

Fixed in

Linux Kernel≥ 5.10.253

Patch & vendor advisories

References

and 27 more references

Related CVEs

Recent high-severity vulnerabilities sharing a weakness type.

Frequently asked

Is CVE-2026-31402 being actively exploited?

CVE-2026-31402 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.58%.

How severe is CVE-2026-31402?

CVE-2026-31402 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.58% probability of exploitation.

Which products are affected by CVE-2026-31402?

Affected products include Linux Kernel.

How do I fix CVE-2026-31402?

Upgrade affected software to a fixed version, for example Linux Kernel 5.10.253 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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