CVE-2026-45983 nfsd: never defer requests during idmap lookup

Medium 5.5 Published 27 May 2026 Updated 27 May 2026

A flaw in the Linux kernel NFS server allows attackers to cause a denial of service by triggering idmap lookup delays that permanently lock session slots.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-45983?

CVE-2026-45983 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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

nfsd: never defer requests during idmap lookup

During v4 request compound arg decoding, some ops (e.g. SETATTR) can trigger idmap lookup upcalls. When those upcall responses get delayed beyond the allowed time limit, cache_check() will mark the request for deferral and cause it to be dropped.

This prevents nfs4svc_encode_compoundres from being executed, and thus the session slot flag NFSD4_SLOT_INUSE never gets cleared. Subsequent client requests will fail with NFSERR_JUKEBOX, given that the slot will be marked as in-use, making the SEQUENCE op fail.

Fix this by making sure that the RQ_USEDEFERRAL flag is always clear during nfs4svc_decode_compoundargs(), since no v4 request should ever be deferred.

Which versions are affected by CVE-2026-45983?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-45983?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-45983 being exploited?

There is no known exploitation of CVE-2026-45983 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as BELL-CVE-2026-45983, DEBIAN-CVE-2026-45983, GHSA-wrmj-c6w7-44cr, ROOT-OS-DEBIAN-11-CVE-2026-45983, ROOT-OS-UBUNTU-2204-CVE-2026-45983, ROOT-OS-UBUNTU-2404-CVE-2026-45983 and 1 more.