CVE-2026-89703 nfsd: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations
A use-after-free in the Linux kernel NFS server allows attackers to cause denial of service or execute arbitrary code via revoked delegations.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89703?
CVE-2026-89703 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: set SC_STATUS_FREED in nfsd4_drop_revoked_stid for delegations
nfsd4_drop_revoked_stid() handles FREE_STATEID for admin-revoked delegations but does not set SC_STATUS_FREED before releasing cl_lock. revoke_delegation() uses this flag to detect whether FREE_STATEID has already processed the delegation -- without it, the freed delegation is added to cl_revoked via list_add(), producing a use-after-free when cl_revoked is later traversed in __destroy_client().
The SC_STATUS_REVOKED path in nfsd4_free_stateid() (line 7983) already sets SC_STATUS_FREED correctly. Apply the same pattern to the SC_STATUS_ADMIN_REVOKED path in nfsd4_drop_revoked_stid().
Which versions are affected by CVE-2026-89703?
How do I fix CVE-2026-89703?
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-2026-89703 being exploited?
There is no known exploitation of CVE-2026-89703 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89703, DEBIAN-CVE-2026-89703, GHSA-4288-gh8m-45g7, UBUNTU-CVE-2026-89703.