CVE-2026-23269 in Linux
Summary
by MITRE • 03/18/2026
In the Linux kernel, the following vulnerability has been resolved:
apparmor: validate DFA start states are in bounds in unpack_pdb
Start states are read from untrusted data and used as indexes into the DFA state tables. The aa_dfa_next() function call in unpack_pdb() will access dfa->tables[YYTD_ID_BASE][start], and if the start state exceeds
the number of states in the DFA, this results in an out-of-bound read.
================================================================== BUG: KASAN: slab-out-of-bounds in aa_dfa_next+0x2a1/0x360 Read of size 4 at addr ffff88811956fb90 by task su/1097 ...
Reject policies with out-of-bounds start states during unpacking to prevent the issue.
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Analysis
by VulDB Data Team • 06/01/2026
The vulnerability identified as CVE-2026-23269 resides within the Linux kernel's AppArmor security module, specifically in the policy unpacking functionality that processes security policies. This issue represents a classic out-of-bounds memory access vulnerability that occurs when the system processes untrusted policy data. The flaw manifests in the unpack_pdb function where start states are extracted from external policy files and subsequently used as direct indices into DFA (Deterministic Finite Automaton) state tables. The underlying technical implementation fails to validate that these start states fall within acceptable bounds, creating a potential avenue for memory corruption and system instability.
The vulnerability operates through a well-defined attack vector where maliciously crafted policy files can contain invalid start state values that exceed the legitimate range of DFA states. When the aa_dfa_next() function attempts to access dfa->tables[YYTD_ID_BASE][start] with an out-of-bounds index, it triggers a slab-out-of-bounds memory access error as demonstrated by the KASAN (Kernel Address Sanitizer) report. This memory corruption occurs because the system assumes that start state values read from untrusted sources are valid and within the expected range of the DFA state table dimensions. The vulnerability directly maps to CWE-129, which addresses insufficient validation of length of input buffers, and represents a clear case of improper input validation in kernel space security modules.
The operational impact of this vulnerability extends beyond simple memory corruption, as it could potentially enable privilege escalation or denial-of-service conditions within the kernel's security framework. When an attacker can manipulate policy files to contain invalid start states, they can cause the kernel to access memory locations outside the intended DFA table boundaries, potentially leading to information disclosure or system crashes. The vulnerability affects systems running Linux kernels with AppArmor enabled and processing external security policies, making it particularly concerning for environments where policy management involves untrusted inputs or automated policy deployment mechanisms.
Mitigation strategies for CVE-2026-23269 focus on implementing proper input validation during the policy unpacking process. The recommended approach involves rejecting policy files that contain start state values exceeding the legitimate DFA state table dimensions before any memory access operations occur. This defensive programming technique aligns with the ATT&CK framework's principle of input validation and can be implemented through boundary checks that ensure start state values fall within the acceptable range of [0, total_states - 1]. System administrators should prioritize kernel updates that include the patched unpack_pdb function, while also implementing strict policy validation procedures for any externally sourced security policies. The fix essentially transforms the vulnerability from an exploitable condition into a controlled validation failure that prevents the out-of-bounds memory access from occurring in the first place.