CVE-2026-23406

Description

In the Linux kernel, the following vulnerability has been resolved: apparmor: fix side-effect bug in match_char() macro usage The match_char() macro evaluates its character parameter multiple times when traversing differential encoding chains. When invoked with *str++, the string pointer advances on each iteration of the inner do-while loop, causing the DFA to check different characters at each iteration and therefore skip input characters. This results in out-of-bounds reads when the pointer advances past the input buffer boundary. [ 94.984676] ================================================================== [ 94.985301] BUG: KASAN: slab-out-of-bounds in aa_dfa_match+0x5ae/0x760 [ 94.985655] Read of size 1 at addr ffff888100342000 by task file/976 [ 94.986319] CPU: 7 UID: 1000 PID: 976 Comm: file Not tainted 6.19.0-rc7-next-20260127 #1 PREEMPT(lazy) [ 94.986322] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 94.986329] Call Trace: [ 94.986341] <TASK> [ 94.986347] dump_stack_lvl+0x5e/0x80 [ 94.986374] print_report+0xc8/0x270 [ 94.986384] ? aa_dfa_match+0x5ae/0x760 [ 94.986388] kasan_report+0x118/0x150 [ 94.986401] ? aa_dfa_match+0x5ae/0x760 [ 94.986405] aa_dfa_match+0x5ae/0x760 [ 94.986408] __aa_path_perm+0x131/0x400 [ 94.986418] aa_path_perm+0x219/0x2f0 [ 94.986424] apparmor_file_open+0x345/0x570 [ 94.986431] security_file_open+0x5c/0x140 [ 94.986442] do_dentry_open+0x2f6/0x1120 [ 94.986450] vfs_open+0x38/0x2b0 [ 94.986453] ? may_open+0x1e2/0x2b0 [ 94.986466] path_openat+0x231b/0x2b30 [ 94.986469] ? __x64_sys_openat+0xf8/0x130 [ 94.986477] do_file_open+0x19d/0x360 [ 94.986487] do_sys_openat2+0x98/0x100 [ 94.986491] __x64_sys_openat+0xf8/0x130 [ 94.986499] do_syscall_64+0x8e/0x660 [ 94.986515] ? count_memcg_events+0x15f/0x3c0 [ 94.986526] ? srso_alias_return_thunk+0x5/0xfbef5 [ 94.986540] ? handle_mm_fault+0x1639/0x1ef0 [ 94.986551] ? vma_start_read+0xf0/0x320 [ 94.986558] ? srso_alias_return_thunk+0x5/0xfbef5 [ 94.986561] ? srso_alias_return_thunk+0x5/0xfbef5 [ 94.986563] ? fpregs_assert_state_consistent+0x50/0xe0 [ 94.986572] ? srso_alias_return_thunk+0x5/0xfbef5 [ 94.986574] ? arch_exit_to_user_mode_prepare+0x9/0xb0 [ 94.986587] ? srso_alias_return_thunk+0x5/0xfbef5 [ 94.986588] ? irqentry_exit+0x3c/0x590 [ 94.986595] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 94.986597] RIP: 0033:0x7fda4a79c3ea Fix by extracting the character value before invoking match_char, ensuring single evaluation per outer loop.

CVSS Details

CVSS Score

7.8

Severity

HIGH

CVSS Vector

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

Configurations (Affected Products)

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

Linux Kernel < 6.19

PoC / Exploit Code

⚠ For Security Research Only

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

python

/*
 * PoC for CVE-2026-23406
 * Triggering the AppArmor slab-out-of-bounds read.
 * This requires a system with AppArmor enabled and a specific policy loaded.
 */

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>

int main(int argc, char **argv) {
    // The specific pattern to trigger the differential encoding chain
    // depends on the AppArmor policy compiled into the kernel or loaded.
    // Based on the crash log, opening a file with a specific name
    // triggers the bug in aa_dfa_match.
    
    const char *filename = "trigger_dfa_bug";
    int fd;

    // Attempt to create and open the file to trigger path permission check
    fd = open(filename, O_RDONLY | O_CREAT, 0644);
    
    if (fd < 0) {
        perror("open failed");
        return 1;
    }

    printf("File opened. Check dmesg for KASAN: slab-out-of-bounds.\n");
    close(fd);
    
    // Clean up
    unlink(filename);
    return 0;
}

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-23406
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-23406
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-23406/
[4] VulDB https://vuldb.com/cve/CVE-2026-23406
[5] https://git.kernel.org/stable/c/0510d1ba0976f97f521feb2b75b0572ea5df3ceb
[6] https://git.kernel.org/stable/c/1fc94f16098213d01e56c97feed9b3ecf0147a37
[7] https://git.kernel.org/stable/c/383b7270faf42564f133134c2fc3c24bbae52615
[8] https://git.kernel.org/stable/c/5a184f7cbdeaad17e16dedf3c17d0cd622edfed8
[9] https://git.kernel.org/stable/c/8756b68edae37ff546c02091989a4ceab3f20abd
[10] https://git.kernel.org/stable/c/b73c1dff8a9d7eeaebabf8097a5b2de192f40913
[11] https://git.kernel.org/stable/c/c7dc56d8b37eda1396feeec3ab1c7ecee5eae31b
[12] https://git.kernel.org/stable/c/f16f2e5936c0f5f0d11fdf10d2be3e47e7108e42

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-23406", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-01T09:16:16.327", "lastModified": "2026-04-24T18:40:51.317", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\napparmor: fix side-effect bug in match_char() macro usage\n\nThe match_char() macro evaluates its character parameter multiple\ntimes when traversing differential encoding chains. When invoked\nwith *str++, the string pointer advances on each iteration of the\ninner do-while loop, causing the DFA to check different characters\nat each iteration and therefore skip input characters.\nThis results in out-of-bounds reads when the pointer advances past\nthe input buffer boundary.\n\n[ 94.984676] ==================================================================\n[ 94.985301] BUG: KASAN: slab-out-of-bounds in aa_dfa_match+0x5ae/0x760\n[ 94.985655] Read of size 1 at addr ffff888100342000 by task file/976\n\n[ 94.986319] CPU: 7 UID: 1000 PID: 976 Comm: file Not tainted 6.19.0-rc7-next-20260127 #1 PREEMPT(lazy)\n[ 94.986322] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014\n[ 94.986329] Call Trace:\n[ 94.986341] <TASK>\n[ 94.986347] dump_stack_lvl+0x5e/0x80\n[ 94.986374] print_report+0xc8/0x270\n[ 94.986384] ? aa_dfa_match+0x5ae/0x760\n[ 94.986388] kasan_report+0x118/0x150\n[ 94.986401] ? aa_dfa_match+0x5ae/0x760\n[ 94.986405] aa_dfa_match+0x5ae/0x760\n[ 94.986408] __aa_path_perm+0x131/0x400\n[ 94.986418] aa_path_perm+0x219/0x2f0\n[ 94.986424] apparmor_file_open+0x345/0x570\n[ 94.986431] security_file_open+0x5c/0x140\n[ 94.986442] do_dentry_open+0x2f6/0x1120\n[ 94.986450] vfs_open+0x38/0x2b0\n[ 94.986453] ? may_open+0x1e2/0x2b0\n[ 94.986466] path_openat+0x231b/0x2b30\n[ 94.986469] ? __x64_sys_openat+0xf8/0x130\n[ 94.986477] do_file_open+0x19d/0x360\n[ 94.986487] do_sys_openat2+0x98/0x100\n[ 94.986491] __x64_sys_openat+0xf8/0x130\n[ 94.986499] do_syscall_64+0x8e/0x660\n[ 94.986515] ? count_memcg_events+0x15f/0x3c0\n[ 94.986526] ? srso_alias_return_thunk+0x5/0xfbef5\n[ 94.986540] ? handle_mm_fault+0x1639/0x1ef0\n[ 94.986551] ? vma_start_read+0xf0/0x320\n[ 94.986558] ? srso_alias_return_thunk+0x5/0xfbef5\n[ 94.986561] ? srso_alias_return_thunk+0x5/0xfbef5\n[ 94.986563] ? fpregs_assert_state_consistent+0x50/0xe0\n[ 94.986572] ? srso_alias_return_thunk+0x5/0xfbef5\n[ 94.986574] ? arch_exit_to_user_mode_prepare+0x9/0xb0\n[ 94.986587] ? srso_alias_return_thunk+0x5/0xfbef5\n[ 94.986588] ? irqentry_exit+0x3c/0x590\n[ 94.986595] entry_SYSCALL_64_after_hwframe+0x76/0x7e\n[ 94.986597] RIP: 0033:0x7fda4a79c3ea\n\nFix by extracting the character value before invoking match_char,\nensuring single evaluation per outer loop."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-125"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.17.1", "versionEndExcluding": "5.10.253", "matchCriteriaId": "E395B1A0-3F3F-4299-9E96-FE513DCFE882"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.11", "versionEndExcluding": "5.15.203", "matchCriteriaId": "20DDB3E9-AABF-4107-ADB0-5362AA067045"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.16", "versionEndExcluding": "6.1.169", "matchCriteriaId": "DBEC0E5D-641C-4E98-A6D9-5799B10CE451"}, {"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": "6.12.77", "matchCriteriaId": "B3D12E00-E42D-4056-B354-BAD4903C03A5"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.18", "matchCriteriaId": "346AD1FB-0CE8-4D9D-8E56-5EB1A4D06199"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", " ... (truncated)