CVE-2025-37949 xenbus: Use kref to track req lifetime
A race condition in the Linux kernel xenbus driver causes a NULL pointer dereference, leading to a system crash.
- 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-2025-37949?
CVE-2025-37949 is a high-severity vulnerability in Debian Debian Linux, published on 20 May 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:
xenbus: Use kref to track req lifetime
Marek reported seeing a NULL pointer fault in the xenbus_thread callstack: BUG: kernel NULL pointer dereference, address: 0000000000000000 RIP: e030:__wake_up_common+0x4c/0x180 Call Trace: <TASK> __wake_up_common_lock+0x82/0xd0 process_msg+0x18e/0x2f0 xenbus_thread+0x165/0x1c0
process_msg+0x18e is req->cb(req). req->cb is set to xs_wake_up(), a thin wrapper around wake_up(), or xenbus_dev_queue_reply(). It seems like it was xs_wake_up() in this case.
It seems like req may have woken up the xs_wait_for_reply(), which kfree()ed the req. When xenbus_thread resumes, it faults on the zero-ed data.
Linux Device Drivers 2nd edition states: "Normally, a wake_up call can cause an immediate reschedule to happen, meaning that other processes might run before wake_up returns." ... which would match the behaviour observed.
Change to keeping two krefs on each request. One for the caller, and one for xenbus_thread. Each will kref_put() when finished, and the last will free it.
This use of kref matches the description in Documentation/core-api/kref.rst
Weakness: CWE-476
Which versions are affected by CVE-2025-37949?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-37949?
Apply the vendor's patch.
Is CVE-2025-37949 being exploited?
There is no known exploitation of CVE-2025-37949 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as BELL-CVE-2025-37949, DEBIAN-CVE-2025-37949, GHSA-v8mr-frx6-j364, ROOT-OS-DEBIAN-11-CVE-2025-37949, ROOT-OS-DEBIAN-12-CVE-2025-37949, ROOT-OS-UBUNTU-2204-CVE-2025-37949 and 2 more.