CVE-2026-90234 NFS: Return a delegation the client fails to record
A flaw in the Linux kernel NFS client causes a denial of service by failing to return delegations, leading to infinite state manager loops.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-90234?
CVE-2026-90234 is a high-severity denial of service vulnerability in Linux, published on 17 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:
NFS: Return a delegation the client fails to record
When an NFS server grants a delegation in an OPEN reply, nfs_inode_set_delegation() records it on the client. However, three of its error flows return without sending DELEGRETURN.
A delegation can be relinquished only by DELEGRETURN (RFC 8881 Section 20.2.4), so dropping one silently leaves the server believing the client still holds it. If the server happens to recall that delegation, the client answers CB_RECALL with NFS4ERR_BADHANDLE because it has no record of the stateid. The server revokes the delegation and moves it onto its cl_revoked list, because the client never sends the FREE_STATEID that would drain it. Every subsequent SEQUENCE reply then carries SEQ4_STATUS_RECALLABLE_STATE_REVOKED, and the client's state manager loops issuing TEST_STATEID across its delegations without ever clearing the condition.
The window is easy to reach now that a server offers a write delegation on any write OPEN: a delegation recalled for one opener races a re-open that the server answers with a fresh write delegation.
Instead of dropping it, hand the delegation back during these error flows.
Which versions are affected by CVE-2026-90234?
How do I fix CVE-2026-90234?
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-2026-90234 being exploited?
There is no known exploitation of CVE-2026-90234 in the wild and no public exploit code.
Sources
Also known as AZL-102395, BELL-CVE-2026-90234, DEBIAN-CVE-2026-90234, GHSA-qx9f-2gch-8fvp, UBUNTU-CVE-2026-90234.