# CVE-2026-31551

> Vulnerability · severity: **MEDIUM** (CVSS 5.5).

## Description

In the Linux kernel, the following vulnerability has been resolved:

wifi: mac80211: Fix static_branch_dec() underflow for aql_disable.

syzbot reported static_branch_dec() underflow in aql_enable_write(). [0]

The problem is that aql_enable_write() does not serialise concurrent
write()s to the debugfs.

aql_enable_write() checks static_key_false(&aql_disable.key) and
later calls static_branch_inc() or static_branch_dec(), but the
state may change between the two calls.

aql_disable does not need to track inc/dec.

Let's use static_branch_enable() and static_branch_disable().

[0]:
val == 0
WARNING: kernel/jump_label.c:311 at __static_key_slow_dec_cpuslocked.part.0+0x107/0x120 kernel/jump_label.c:311, CPU#0: syz.1.3155/20288
Modules linked in:
CPU: 0 UID: 0 PID: 20288 Comm: syz.1.3155 Tainted: G     U       L      syzkaller #0 PREEMPT(full)
Tainted: [U]=USER, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:__static_key_slow_dec_cpuslocked.part.0+0x107/0x120 kernel/jump_label.c:311
Code: f2 c9 ff 5b 5d c3 cc cc cc cc e8 54 f2 c9 ff 48 89 df e8 ac f9 ff ff eb ad e8 45 f2 c9 ff 90 0f 0b 90 eb a2 e8 3a f2 c9 ff 90 <0f> 0b 90 eb 97 48 89 df e8 5c 4b 33 00 e9 36 ff ff ff 0f 1f 80 00
RSP: 0018:ffffc9000b9f7c10 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffffffff9b3e5d40 RCX: ffffffff823c57b4
RDX: ffff8880285a0000 RSI: ffffffff823c5846 RDI: ffff8880285a0000
RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 000000000000000a
R13: 1ffff9200173ef88 R14: 0000000000000001 R15: ffffc9000b9f7e98
FS:  00007f530dd726c0(0000) GS:ffff8881245e3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001140 CR3: 000000007cc4a000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __static_key_slow_dec_cpuslocked kernel/jump_label.c:297 [inline]
 __static_key_slow_dec kernel/jump_label.c:321 [inline]
 static_key_slow_dec+0x7c/0

## Key facts

- **CVE ID:** CVE-2026-31551
- **Published:** 2026-04-24
- **CVSS severity:** MEDIUM
- **CVSS base score:** 5.5
- **CWE codes:** CWE-191

## Affected products

- `linux:linux_kernel`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31551

## Citation

> AI Analytics. CVE-2026-31551. Retrieved 2026-09-03 from https://api.ai-analytics.org/cve/CVE-2026-31551. Derived from NIST NVD. Licensed CC0.

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