CVE-2025-38443 nbd: fix uaf in nbd_genl_connect() error path
A use-after-free in the Linux kernel NBD driver allows local attackers to potentially execute code or escalate privileges via crafted netlink messages.
- 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-2025-38443?
CVE-2025-38443 is a high-severity use after free vulnerability in Debian Debian Linux, published on 25 Jul 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:
nbd: fix uaf in nbd_genl_connect() error path
There is a use-after-free issue in nbd:
block nbd6: Receive control failed (result -104) block nbd6: shutting down sockets ================================================================== BUG: KASAN: slab-use-after-free in recv_work+0x694/0xa80 drivers/block/nbd.c:1022 Write of size 4 at addr ffff8880295de478 by task kworker/u33:0/67
CPU: 2 UID: 0 PID: 67 Comm: kworker/u33:0 Not tainted 6.15.0-rc5-syzkaller-00123-g2c89c1b655c0 #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Workqueue: nbd6-recv recv_work Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0xc3/0x670 mm/kasan/report.c:521 kasan_report+0xe0/0x110 mm/kasan/report.c:634 check_region_inline mm/kasan/generic.c:183 [inline] kasan_check_range+0xef/0x1a0 mm/kasan/generic.c:189 instrument_atomic_read_write include/linux/instrumented.h:96 [inline] atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline] recv_work+0x694/0xa80 drivers/block/nbd.c:1022 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3319 [inline] worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400 kthread+0x3c2/0x780 kernel/kthread.c:464 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK>
nbd_genl_connect() does not properly stop the device on certain error paths after nbd_start_device() has been called. This causes the error path to put nbd->config while recv_work continue to use the config after putting it, leading to use-after-free in recv_work.
This patch moves nbd_start_device() after the backend file creation.
Weakness: CWE-416
Which versions are affected by CVE-2025-38443?
It affects 2 products.
Products include Debian Debian Linux, Linux kernel.
How do I fix CVE-2025-38443?
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-2025-38443 being exploited?
There is no known exploitation of CVE-2025-38443 in the wild and no public exploit code.
Other vulnerabilities in Debian Debian Linux
Sources
Also known as AZL-65795, AZL-72923, BELL-CVE-2025-38443, DEBIAN-CVE-2025-38443, GHSA-2rf4-w4q3-rjcw, ROOT-OS-DEBIAN-12-CVE-2025-38443 and 3 more.