CVE-2026-23269: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-23269 is an out-of-bounds read vulnerability in the Linux kernel's AppArmor security module, specifically in the unpack_pdb() function responsible for unpacking AppArmor policy database files. The flaw arises because DFA (Deterministic Finite Automaton) start states are read from untrusted policy data and used directly as array indexes into DFA state tables without bounds validation. It was published on March 18, 2026, and affects Linux kernel versions from 3.4 through multiple stable branches, with fixed versions including 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8, and 7.0-rc4. The vulnerability carries a CVSS v3.1 base score of 7.1 (High) (Red Hat Advisory, Red Hat Bugzilla).

The root cause is classified as CWE-125 (Out-of-bounds Read). In the unpack_pdb() function within the AppArmor kernel module, start state values are deserialized from untrusted AppArmor policy files and passed directly to aa_dfa_next(), which uses them as indexes into dfa->tables[YYTD_ID_BASE][start]. If a crafted policy specifies a start state index exceeding the actual number of DFA states, the kernel performs a slab-out-of-bounds read, as confirmed by KASAN output: BUG: KASAN: slab-out-of-bounds in aa_dfa_next+0x2a1/0x360. The attack vector is local (AV:L), requiring low privileges (PR:L), and the precondition is that the attacker must have the ability to load AppArmor policies — typically a privileged local user. The fix rejects policies with out-of-bounds start states during the unpacking phase (Red Hat Bugzilla, Feedly).

Successful exploitation allows a local attacker with policy-load privileges to trigger an out-of-bounds read of kernel slab memory, potentially disclosing sensitive kernel data (confidentiality impact: High) and causing a kernel crash or system instability (availability impact: High). There is no integrity impact. The vulnerability is confined to the local system and does not directly enable remote code execution or lateral movement, but kernel memory disclosure could facilitate further privilege escalation attacks (Red Hat Advisory, Feedly).

1. Gain local access: Obtain a local user account on a vulnerable Linux system running an affected kernel version (3.4 through pre-patch versions) with AppArmor enabled.
2. Acquire policy-load privileges: Ensure the account has the capability to load AppArmor policies (e.g., via CAP_MAC_ADMIN or equivalent administrative rights).
3. Craft a malicious AppArmor policy: Create a specially crafted AppArmor policy binary (.pdb format) in which the DFA start state value is set to an index exceeding the actual number of states in the DFA state table.
4. Load the malicious policy: Use apparmor_parser or a direct kernel interface to load the crafted policy, triggering the unpack_pdb() code path.
5. Trigger out-of-bounds read: The kernel's aa_dfa_next() function accesses dfa->tables[YYTD_ID_BASE][start] with the out-of-bounds index, reading kernel slab memory beyond the allocated buffer.
6. Achieve objective: Depending on the memory layout, the attacker may leak sensitive kernel memory contents (e.g., pointers, credentials) or trigger a kernel panic, causing a denial of service (Red Hat Bugzilla, Feedly).

• Logs: Kernel logs (dmesg or /var/log/kern.log) containing KASAN reports such as BUG: KASAN: slab-out-of-bounds in aa_dfa_next+0x2a1/0x360 or Read of size 4 at addr followed by a kernel address.
• Logs: AppArmor audit logs showing unexpected policy load attempts, particularly from non-standard users or processes (check /var/log/audit/audit.log for type=AVC or type=APPARMOR entries).
• Process: Unusual invocation of apparmor_parser by non-root or non-administrative users, or from unexpected parent processes.
• File System: Presence of unexpected or malformed AppArmor policy files (.pdb or compiled policy binaries) in /etc/apparmor.d/ or temporary directories.
• System: Unexpected kernel panics or system crashes on systems with AppArmor enabled, potentially indicating a failed or successful exploitation attempt.

Patches are available across multiple stable kernel branches: upgrade to Linux kernel 5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18, 6.19.8, or 7.0-rc4 (or later). Distribution-specific updates have been released by Red Hat, Ubuntu (USN-8141-1, USN-8152-1, USN-8163-1, USN-8201-1, USN-8224-1, USN-8243-1, USN-8266-1, USN-8267-1), SUSE (SUSE-SU-2026:0961-1, SUSE-SU-2026:1041-1, SUSE-SU-2026:1131-1, and others), and openSUSE. As a workaround, restrict the ability to load AppArmor policies to trusted administrative users only, and implement file integrity monitoring on AppArmor policy files to detect unauthorized modifications (Red Hat Advisory, Ubuntu Advisory, Microsoft MSRC).

Canonical published a blog post titled "AppArmor vulnerability fixes available" shortly after disclosure, highlighting the significance of the AppArmor flaws (Canonical Blog). Qualys Threat Research published a detailed analysis titled "CrackArmor: Critical AppArmor Flaws Enable Local Privilege Escalation to Root" in March 2026, grouping this CVE with related AppArmor vulnerabilities and providing broader context for defenders (Qualys Blog). The vulnerability was also discussed on the oss-security mailing list, with multiple threads covering the AppArmor flaw cluster (oss-sec).