CyberSecBulletin
CVE-2026-23406NVD status: Analyzed

Linux: Out-of-bounds Read

Published Updated By the CyberSecBulletin desk

CVE-2026-23406 is a high-severity out-of-bounds read vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions c7dc56d8b37eda1396feeec3ab1c7ecee5eae31b, f16f2e5936c0f5f0d11fdf10d2be3e47e7108e42, 1fc94f16098213d01e56c97feed9b3ecf0147a37 as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.18% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Linux to c7dc56d8b37eda1396feeec3ab1c7ecee5eae31b or f16f2e5936c0f5f0d11fdf10d2be3e47e7108e42 or 1fc94f16098213d01e56c97feed9b3ecf0147a37 or 5a184f7cbdeaad17e16dedf3c17d0cd622edfed8, whichever matches your release line, or a later version.
  2. Update Linux Kernel to 5.10.253 or 5.15.203 or 6.1.169 or 6.6.130, whichever matches your release line, or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
LinuxLinux074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, c7dc56d8b37eda1396feeec3ab1c7ecee5eae31b; 074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, f16f2e5936c0f5f0d11fdf10d2be3e47e7108e42; 074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, 1fc94f16098213d01e56c97feed9b3ecf0147a37; 074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, 5a184f7cbdeaad17e16dedf3c17d0cd622edfed8; 074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, b73c1dff8a9d7eeaebabf8097a5b2de192f40913; 074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, 0510d1ba0976f97f521feb2b75b0572ea5df3ceb; 074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, 383b7270faf42564f133134c2fc3c24bbae52615; 074c1cd798cb0b481d7eaa749b64aa416563c053 up to, but not including, 8756b68edae37ff546c02091989a4ceab3f20abd; and 1 more rangesc7dc56d8b37eda1396feeec3ab1c7ecee5eae31b, f16f2e5936c0f5f0d11fdf10d2be3e47e7108e42, 1fc94f16098213d01e56c97feed9b3ecf0147a37, 5a184f7cbdeaad17e16dedf3c17d0cd622edfed8, b73c1dff8a9d7eeaebabf8097a5b2de192f40913, 0510d1ba0976f97f521feb2b75b0572ea5df3ceb
LinuxLinux Kernel4.17.1 up to, but not including, 5.10.253; 5.11 up to, but not including, 5.15.203; 5.16 up to, but not including, 6.1.169; 6.2 up to, but not including, 6.6.130; 6.7 up to, but not including, 6.12.77; 6.13 up to, but not including, 6.18.18; 6.19 up to, but not including, 6.19.8; 4.17; and 1 more ranges5.10.253, 5.15.203, 6.1.169, 6.6.130, 6.12.77, 6.18.18

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Read

The product reads data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that provides appropriate memory abstractions.

More Out-of-bounds Read vulnerabilities (CWE-125)

Timeline

  1. CVE record published.
  2. Record last changed materially (score, affected products, status or references).

References

Recent Out-of-bounds Read vulnerabilities

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