CVE-2025-38534 netfs: Fix copy-to-cache so that it performs collection with ceph+fscache
A logic error in the Linux kernel's netfs copy-to-cache mechanism causes requests to hang when using Ceph with fscache, leading to a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-38534?
CVE-2025-38534 is a medium-severity denial of service vulnerability in Linux kernel, published on 16 Aug 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
netfs: Fix copy-to-cache so that it performs collection with ceph+fscache
The netfs copy-to-cache that is used by Ceph with local caching sets up a new request to write data just read to the cache. The request is started and then left to look after itself whilst the app continues. The request gets notified by the backing fs upon completion of the async DIO write, but then tries to wake up the app because NETFS_RREQ_OFFLOAD_COLLECTION isn't set - but the app isn't waiting there, and so the request just hangs.
Fix this by setting NETFS_RREQ_OFFLOAD_COLLECTION which causes the notification from the backing filesystem to put the collection onto a work queue instead.
Which versions are affected by CVE-2025-38534?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-38534?
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-2025-38534 being exploited?
There is no known exploitation of CVE-2025-38534 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-38534, GHSA-6rpm-59f8-4x64, UBUNTU-CVE-2025-38534.