CVE-2026-89677 nfsd: fix possible fh_compose of wrong dentry in nfsd4_create_file()
A use-after-free vulnerability in the Linux kernel NFS server allows attackers to potentially execute code or cause a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89677?
CVE-2026-89677 is a critical use after free vulnerability in Linux, published on 11 Sep 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:
nfsd: fix possible fh_compose of wrong dentry in nfsd4_create_file()
dentry_create() can hypothetically provide a different dentry than the one passed in. This could happen, for example, if the exported filesystem is NFS, and the server returned to OPEN a filehandle which matched a directory that was already in the dcache. Clearly this would not be expected!
If this were to happen the dentry (child) that was already stored in resfhp could be freed and later dereferenced.
We shouldn't call fh_compose() until we are certain that we have the final dentry, so this patch moved the fh_compose() call to two places: one for the case where the target already exists, and one after dentry_create() where it was created.
Which versions are affected by CVE-2026-89677?
How do I fix CVE-2026-89677?
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-2026-89677 being exploited?
There is no known exploitation of CVE-2026-89677 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-89677, GHSA-rgqw-p3pf-j5p9, UBUNTU-CVE-2026-89677.