CVE-2026-74506 afs: Fix UAF when sending a message
A use-after-free vulnerability in the Linux kernel AFS module allows attackers to cause denial of service or potentially execute code via race conditions.
- 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-2026-74506?
CVE-2026-74506 is a high-severity use after free vulnerability in Linux, published on 15 Aug 2026. 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:
afs: Fix UAF when sending a message
In afs_make_call(), there's a race with async call reception and destruction. If a call is dispatched that doesn't have call->write_iter set (used to specify the data content for FS.StoreData), then the first rxrpc_kernel_send_data() will not set MSG_MORE in the msghdr.
Once rxrpc_send_data() queues the last request packet, the response could come in at any time and cause the call to be completed and put. However, afs_make_call() will look at the call again to see it ->write_iter should be handled - something it's only allowed to do if it has its own ref on the call. Whilst this is the case for synchronous calls, it isn't true for async calls such as FS.FetchData.
There's also a potential UAF in afs_make_call() in the event that an asynchronous call is being sent, but the call fails in some way (e.g. it gets aborted from the server). The problem there is that afs_make_call() tries to abort a call if the rxrpc send fails, but the asynchronous notification from rxrpc may have caused the afs_call to be torn down.
generic/650 plays games with randomly taking CPUs offline, and can interject a significant delay such that the call is deallocated before afs_make_call() gets to check call->write_iter - and a UAF ensues (caught by KASAN).
BUG: KASAN: slab-use-after-free in afs_make_call+0x1c90/0x2210 [kafs] Read of size 8 at addr ffff888035e050e8 by task fsstress/1409
Fix this by making afs_make_op_call() give the op->call its own ref rather than transferring the caller's ref to it and then dropping the ref when afs_make_call() returns.
This also means that the afs_make_call() func never loses its ref on the call now.
Which versions are affected by CVE-2026-74506?
How do I fix CVE-2026-74506?
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-2026-74506 being exploited?
There is no known exploitation of CVE-2026-74506 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-74506, DEBIAN-CVE-2026-74506, GHSA-437r-ppxq-jxxh, UBUNTU-CVE-2026-74506.