CVE-2026-23407
Published: 01 April 2026
Summary
CVE-2026-23407 is a high-severity Out-of-bounds Read (CWE-125) vulnerability in Linux Linux Kernel. Its CVSS base score is 7.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 3.5th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-10 (Information Input Validation) and SI-2 (Flaw Remediation).
Threat & Defense at a Glance
Threat & Defense Details
Mitigating Controls (NIST 800-53 r5)AI
Timely remediation through kernel patching directly addresses the missing bounds check in verify_dfa() by enforcing validation on all DEFAULT_TABLE entries.
Requires bounds checking and validation of malformed DFA inputs, such as DEFAULT_TABLE[j] indices against state_count, during AppArmor policy loading.
Kernel memory protections like KASLR and slab allocators mitigate the impact of out-of-bounds reads and writes in verify_dfa() even if validation fails.
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Local kernel out-of-bounds R/W in AppArmor DFA validation directly enables privilege escalation from low-privileged user space via policy loading paths.
NVD Description
In the Linux kernel, the following vulnerability has been resolved: apparmor: fix missing bounds check on DEFAULT table in verify_dfa() The verify_dfa() function only checks DEFAULT_TABLE bounds when the state is not differentially encoded. When the verification loop traverses the…
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differential encoding chain, it reads k = DEFAULT_TABLE[j] and uses k as an array index without validation. A malformed DFA with DEFAULT_TABLE[j] >= state_count, therefore, causes both out-of-bounds reads and writes. [ 57.179855] ================================================================== [ 57.180549] BUG: KASAN: slab-out-of-bounds in verify_dfa+0x59a/0x660 [ 57.180904] Read of size 4 at addr ffff888100eadec4 by task su/993 [ 57.181554] CPU: 1 UID: 0 PID: 993 Comm: su Not tainted 6.19.0-rc7-next-20260127 #1 PREEMPT(lazy) [ 57.181558] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 57.181563] Call Trace: [ 57.181572] <TASK> [ 57.181577] dump_stack_lvl+0x5e/0x80 [ 57.181596] print_report+0xc8/0x270 [ 57.181605] ? verify_dfa+0x59a/0x660 [ 57.181608] kasan_report+0x118/0x150 [ 57.181620] ? verify_dfa+0x59a/0x660 [ 57.181623] verify_dfa+0x59a/0x660 [ 57.181627] aa_dfa_unpack+0x1610/0x1740 [ 57.181629] ? __kmalloc_cache_noprof+0x1d0/0x470 [ 57.181640] unpack_pdb+0x86d/0x46b0 [ 57.181647] ? srso_alias_return_thunk+0x5/0xfbef5 [ 57.181653] ? srso_alias_return_thunk+0x5/0xfbef5 [ 57.181656] ? aa_unpack_nameX+0x1a8/0x300 [ 57.181659] aa_unpack+0x20b0/0x4c30 [ 57.181662] ? srso_alias_return_thunk+0x5/0xfbef5 [ 57.181664] ? stack_depot_save_flags+0x33/0x700 [ 57.181681] ? kasan_save_track+0x4f/0x80 [ 57.181683] ? kasan_save_track+0x3e/0x80 [ 57.181686] ? __kasan_kmalloc+0x93/0xb0 [ 57.181688] ? __kvmalloc_node_noprof+0x44a/0x780 [ 57.181693] ? aa_simple_write_to_buffer+0x54/0x130 [ 57.181697] ? policy_update+0x154/0x330 [ 57.181704] aa_replace_profiles+0x15a/0x1dd0 [ 57.181707] ? srso_alias_return_thunk+0x5/0xfbef5 [ 57.181710] ? __kvmalloc_node_noprof+0x44a/0x780 [ 57.181712] ? aa_loaddata_alloc+0x77/0x140 [ 57.181715] ? srso_alias_return_thunk+0x5/0xfbef5 [ 57.181717] ? _copy_from_user+0x2a/0x70 [ 57.181730] policy_update+0x17a/0x330 [ 57.181733] profile_replace+0x153/0x1a0 [ 57.181735] ? rw_verify_area+0x93/0x2d0 [ 57.181740] vfs_write+0x235/0xab0 [ 57.181745] ksys_write+0xb0/0x170 [ 57.181748] do_syscall_64+0x8e/0x660 [ 57.181762] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 57.181765] RIP: 0033:0x7f6192792eb2 Remove the MATCH_FLAG_DIFF_ENCODE condition to validate all DEFAULT_TABLE entries unconditionally.
Deeper analysisAI
CVE-2026-23407 affects the Linux kernel's AppArmor subsystem, specifically the verify_dfa() function responsible for validating deterministic finite automata (DFA) used in policy enforcement. The vulnerability stems from a missing bounds check on DEFAULT_TABLE entries when processing differentially encoded states. In such cases, the function reads an index k from DEFAULT_TABLE[j] without validating that k is less than the state_count, enabling a malformed DFA to cause out-of-bounds reads and writes, as detected by KASAN in kernel version 6.19.0-rc7-next-20260127.
A local attacker with low privileges (AV:L/AC:L/PR:L/UI:N) can exploit this during AppArmor policy loading, such as via the policy_update() path triggered by writes to policy files (e.g., through aa_replace_profiles() and aa_dfa_unpack()). The stack trace indicates exploitation from user-space processes like 'su' interacting with kernel interfaces, leading to slab-out-of-bounds access in verify_dfa(). Successful exploitation yields high impacts on confidentiality, integrity, and availability (C:H/I:H/A:H), rated at CVSS 7.8 (CVSS:3.1), and is classified under CWE-125 (Out-of-bounds Read).
Patch commits in the Linux kernel stable repository address the issue by removing the MATCH_FLAG_DIFF_ENCODE condition in verify_dfa(), enforcing unconditional bounds validation on all DEFAULT_TABLE entries. Key references include https://git.kernel.org/stable/c/22094c996968a7c5b59cd3fc9fcbdfdd46d02fec, https://git.kernel.org/stable/c/555829fd91eaf0711e369b0a92aecb0f0aa3281f, https://git.kernel.org/stable/c/5a68e46dfe0c8c8ffc6f425ebc4cae6238566ecc, https://git.kernel.org/stable/c/76b4d36c5122866452d34d8f79985e191f9c3831, and https://git.kernel.org/stable/c/7c7cf05e0606f554c467e3a4dc49e2e578a755b4.
Details
- CWE(s)