# CVE-2025-38443: nbd: fix uaf in nbd_genl_connect() error path

Status: published. Published: 2025-07-25. Updated: 2026-11-05.

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.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 6497ef8df568afbf5f3e38825a4590ff41611a54; < cb121c47f364b51776c4db904a6a5a90ab0a7ec5 (affected, git); ≥ 6497ef8df568afbf5f3e38825a4590ff41611a54; < 91fa560c73a8126868848ed6cd70607cbf8d87e2 (affected, git); ≥ 6497ef8df568afbf5f3e38825a4590ff41611a54; < d46186eb7bbd9a11c145120f2d77effa8d4d44c2 (affected, git); ≥ 6497ef8df568afbf5f3e38825a4590ff41611a54; < 8586552df591e0a367eff44af0c586213eeecc3f (affected, git); ≥ 6497ef8df568afbf5f3e38825a4590ff41611a54; < 002aca89753f666d878ca0eb8584c372684ac4ba (affected, git); ≥ 6497ef8df568afbf5f3e38825a4590ff41611a54; < aa9552438ebf015fc5f9f890dbfe39f0c53cf37e (affected, git). Source: CNA: Linux
- Linux / Linux: 5.14 (affected); ≥ 0; < 5.14 (unaffected, semver); ≥ 5.15.189; ≤ 5.15.* (unaffected, semver); ≥ 6.1.146; ≤ 6.1.* (unaffected, semver); ≥ 6.6.99; ≤ 6.6.* (unaffected, semver); ≥ 6.12.39; ≤ 6.12.* (unaffected, semver); ≥ 6.15.7; ≤ 6.15.* (unaffected, semver); ≥ 6.16; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.18% as of 2026-11-05; percentile 7.99%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/cb121c47f364b51776c4db904a6a5a90ab0a7ec5 (CNA: Linux)

- https://git.kernel.org/stable/c/91fa560c73a8126868848ed6cd70607cbf8d87e2 (CNA: Linux)

- https://git.kernel.org/stable/c/d46186eb7bbd9a11c145120f2d77effa8d4d44c2 (CNA: Linux)

- https://git.kernel.org/stable/c/8586552df591e0a367eff44af0c586213eeecc3f (CNA: Linux)

- https://git.kernel.org/stable/c/002aca89753f666d878ca0eb8584c372684ac4ba (CNA: Linux)

- https://git.kernel.org/stable/c/aa9552438ebf015fc5f9f890dbfe39f0c53cf37e (CNA: Linux)

- https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html (ADP: CVE)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2025-38443; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2025-38443; retrieved 2026-11-05; source updated Not reported

Revision: 5a0a39403caba0cdee8a25e65da5d51b71ec7a5a08f22d1ee20d13477dfb77b2

Canonical: https://y2.dev/cve/CVE-2025-38443

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