CVE-2025-39688 nfsd: allow SC_STATUS_FREEABLE when searching via nfs4_lookup_stateid()
A logic error in the Linux kernel NFS server causes revoked delegations to be mishandled, potentially leading to 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-2025-39688?
CVE-2025-39688 is a high-severity denial of service vulnerability in Linux kernel, published on 18 Apr 2025. 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: allow SC_STATUS_FREEABLE when searching via nfs4_lookup_stateid()
The pynfs DELEG8 test fails when run against nfsd. It acquires a delegation and then lets the lease time out. It then tries to use the deleg stateid and expects to see NFS4ERR_DELEG_REVOKED, but it gets bad NFS4ERR_BAD_STATEID instead.
When a delegation is revoked, it's initially marked with SC_STATUS_REVOKED, or SC_STATUS_ADMIN_REVOKED and later, it's marked with the SC_STATUS_FREEABLE flag, which denotes that it is waiting for s FREE_STATEID call.
nfs4_lookup_stateid() accepts a statusmask that includes the status flags that a found stateid is allowed to have. Currently, that mask never includes SC_STATUS_FREEABLE, which means that revoked delegations are (almost) never found.
Add SC_STATUS_FREEABLE to the always-allowed status flags, and remove it from nfsd4_delegreturn() since it's now always implied.
Which versions are affected by CVE-2025-39688?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-39688?
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-2025-39688 being exploited?
There is no known exploitation of CVE-2025-39688 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-39688, DEBIAN-CVE-2025-39688, GHSA-53x5-v4j3-g5xm, UBUNTU-CVE-2025-39688.