CVE-2026-31403 NFSD: Hold net reference for the lifetime of /proc/fs/nfs/exports fd
A use-after-free vulnerability in the Linux kernel NFSD module allows attackers to cause denial of service or execute code via race conditions during network namespace teardown.
- 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-2026-31403?
CVE-2026-31403 is a high-severity use after free vulnerability in Linux kernel, published on 3 Apr 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: Hold net reference for the lifetime of /proc/fs/nfs/exports fd
The /proc/fs/nfs/exports proc entry is created at module init and persists for the module's lifetime. exports_proc_open() captures the caller's current network namespace and stores its svc_export_cache in seq->private, but takes no reference on the namespace. If the namespace is subsequently torn down (e.g. container destruction after the opener does setns() to a different namespace), nfsd_net_exit() calls nfsd_export_shutdown() which frees the cache. Subsequent reads on the still-open fd dereference the freed cache_detail, walking a freed hash table.
Hold a reference on the struct net for the lifetime of the open file descriptor. This prevents nfsd_net_exit() from running -- and thus prevents nfsd_export_shutdown() from freeing the cache -- while any exports fd is open. cache_detail already stores its net pointer (cd->net, set by cache_create_net()), so exports_release() can retrieve it without additional per-file storage.
Weakness: CWE-416
Which versions are affected by CVE-2026-31403?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31403?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-31403 being exploited?
There is no known exploitation of CVE-2026-31403 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31403, DEBIAN-CVE-2026-31403, GHSA-85m5-f4f3-q6f5, ROOT-OS-DEBIAN-11-CVE-2026-31403, ROOT-OS-DEBIAN-12-CVE-2026-31403, ROOT-OS-DEBIAN-13-CVE-2026-31403 and 3 more.