# CVE-2026-31551: wifi: mac80211: Fix static_branch_dec() underflow for aql_disable.

Status: published. Published: 2026-04-24. Updated: 2026-11-05.

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/0xc0 kernel/jump_label.c:336
 aql_enable_write+0x2b2/0x310 net/mac80211/debugfs.c:343
 short_proxy_write+0x133/0x1a0 fs/debugfs/file.c:383
 vfs_write+0x2aa/0x1070 fs/read_write.c:684
 ksys_pwrite64 fs/read_write.c:793 [inline]
 __do_sys_pwrite64 fs/read_write.c:801 [inline]
 __se_sys_pwrite64 fs/read_write.c:798 [inline]
 __x64_sys_pwrite64+0x1eb/0x250 fs/read_write.c:798
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f530cf9aeb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f530dd72028 EFLAGS: 00000246 ORIG_RAX: 0000000000000012
RAX: ffffffffffffffda RBX: 00007f530d215fa0 RCX: 00007f530cf9aeb9
RDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000010
RBP: 00007f530d008c1f R08: 0000000000000000 R09: 0000000000000000
R10: 4200000000000005 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f530d216038 R14: 00007f530d215fa0 R15: 00007ffde89fb978
 </TASK>

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ e908435e402aff23c9b0b3c59c7cd12b08b681b0; < 787152497ac763deab16f6f4b7ce79aaeb3eb7e8 (affected, git); ≥ e908435e402aff23c9b0b3c59c7cd12b08b681b0; < 8bb90ff77326c34e75b573b1febdd9586fec5aba (affected, git); ≥ e908435e402aff23c9b0b3c59c7cd12b08b681b0; < 256f7d4c11235d0569f78413c41dc89d2dc1557c (affected, git); ≥ e908435e402aff23c9b0b3c59c7cd12b08b681b0; < 29a1a350afcd28a2150bd73b8bd83eac3480f13e (affected, git); ≥ e908435e402aff23c9b0b3c59c7cd12b08b681b0; < 5ba05436f15d16ae7ab04b880e8bf8d440be892b (affected, git); ≥ e908435e402aff23c9b0b3c59c7cd12b08b681b0; < b24763d32d5b4ada766deca4b42d6766272fef0c (affected, git); ≥ e908435e402aff23c9b0b3c59c7cd12b08b681b0; < b94ae8e0d5fe1bdbbfdc3854ff6ce98f6876a828 (affected, git). Source: CNA: Linux
- Linux / Linux: 5.12 (affected); ≥ 0; < 5.12 (unaffected, semver); ≥ 5.15.203; ≤ 5.15.* (unaffected, semver); ≥ 6.1.167; ≤ 6.1.* (unaffected, semver); ≥ 6.6.130; ≤ 6.6.* (unaffected, semver); ≥ 6.12.78; ≤ 6.12.* (unaffected, semver); ≥ 6.18.20; ≤ 6.18.* (unaffected, semver); ≥ 6.19.10; ≤ 6.19.* (unaffected, semver); ≥ 7.0; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: 0.12% as of 2026-11-05; percentile 2.05%

- 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/787152497ac763deab16f6f4b7ce79aaeb3eb7e8 (CNA: Linux)

- https://git.kernel.org/stable/c/8bb90ff77326c34e75b573b1febdd9586fec5aba (CNA: Linux)

- https://git.kernel.org/stable/c/256f7d4c11235d0569f78413c41dc89d2dc1557c (CNA: Linux)

- https://git.kernel.org/stable/c/29a1a350afcd28a2150bd73b8bd83eac3480f13e (CNA: Linux)

- https://git.kernel.org/stable/c/5ba05436f15d16ae7ab04b880e8bf8d440be892b (CNA: Linux)

- https://git.kernel.org/stable/c/b24763d32d5b4ada766deca4b42d6766272fef0c (CNA: Linux)

- https://git.kernel.org/stable/c/b94ae8e0d5fe1bdbbfdc3854ff6ce98f6876a828 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-31551; retrieved 2026-11-05; source updated 2026-11-05

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-31551; retrieved 2026-11-05; source updated Not reported

Revision: cc4f8113e28b5e2fa1d4449d73a8bc0aa57bd3b12e541e48b65cb67ceb04ba8d

Canonical: https://y2.dev/cve/CVE-2026-31551

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