CVE-2025-37949: Debian Linux

Medium severity, CVSS 5.5. EPSS: 0.2% chance of exploitation in the next 30 days.

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

Affected products

• Debian Debian Linux: version 11.0 only
• Linux Linux Kernel: from 4.11, before 5.4.294 (fixed in 5.4.294); from 5.5, before 5.10.238 (fixed in 5.10.238); from 5.11, before 5.15.183 (fixed in 5.15.183); from 5.16, before 6.1.139 (fixed in 6.1.139); from 6.2, before 6.6.91 (fixed in 6.6.91); from 6.7, before 6.12.29 (fixed in 6.12.29); …

Published 2025-05-20. Last modified 2026-07-30.