CVE-2026-74315 lockd: Avoid hashing uninitialized bytes in nlm4svc_lookup_file()
An attacker can read uninitialized kernel memory via NLMv4 file handle hashing, potentially leaking sensitive data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-74315?
CVE-2026-74315 is a critical vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
lockd: Avoid hashing uninitialized bytes in nlm4svc_lookup_file()
file_hash() digests the first LOCKD_FH_HASH_SIZE bytes of nfs_fh.data when bucketing nlm_files[], independent of fh.size. Commit 3de744ee4e45 ("lockd: Use xdrgen XDR functions for the NLMv4 TEST procedure") set .pc_argzero to zero for the converted procedures and moved file-handle population into nlm4svc_lookup_file(), which copies only xdr_lock->fh.len bytes into lock->fh.data.
When an NLMv4 client presents a file handle shorter than LOCKD_FH_HASH_SIZE, bytes fh.len..31 retain whatever the argument buffer held from an earlier request. The same wire handle then hashes to different buckets across calls; nlm_lookup_file() misses the existing nlm_file entry, and lock-state lookups fail.
Zero only the tail bytes that file_hash() would otherwise consume. Handles of LOCKD_FH_HASH_SIZE or larger already populate every byte that file_hash() reads.
Which versions are affected by CVE-2026-74315?
How do I fix CVE-2026-74315?
Apply the vendor's patch.
Is CVE-2026-74315 being exploited?
There is no known exploitation of CVE-2026-74315 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-74315, GHSA-5v8r-fj78-ffg6, UBUNTU-CVE-2026-74315.