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CVE-2026-23406— apparmor: fix side-effect bug in match_char() macro usage

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于match_char宏存在副作用错误，可能导致越界读取。

CVSS 7.8 · High EPSS 0.18% · P7

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 074c1cd798cb0b481d7eaa749b64aa416563c053< c7dc56d8b37eda1396feeec3ab1c7ecee5eae31b affected
074c1cd798cb0b481d7eaa749b64aa416563c053< f16f2e5936c0f5f0d11fdf10d2be3e47e7108e42 affected
074c1cd798cb0b481d7eaa749b64aa416563c053< 1fc94f16098213d01e56c97feed9b3ecf0147a37 affected
074c1cd798cb0b481d7eaa749b64aa416563c053< 5a184f7cbdeaad17e16dedf3c17d0cd622edfed8 affected
074c1cd798cb0b481d7eaa749b64aa416563c053< b73c1dff8a9d7eeaebabf8097a5b2de192f40913 affected
074c1cd798cb0b481d7eaa749b64aa416563c053< 0510d1ba0976f97f521feb2b75b0572ea5df3ceb affected
074c1cd798cb0b481d7eaa749b64aa416563c053< 383b7270faf42564f133134c2fc3c24bbae52615 affected
074c1cd798cb0b481d7eaa749b64aa416563c053< 8756b68edae37ff546c02091989a4ceab3f20abd affected
… +10 more rows
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I. Basic Information for CVE-2026-23406

Vulnerability Information
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Vulnerability Title
apparmor: fix side-effect bug in match_char() macro usage
Source: CVE Program / CVE List V5
Vulnerability 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: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于match_char宏存在副作用错误，可能导致越界读取。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 074c1cd798cb0b481d7eaa749b64aa416563c053 ~ c7dc56d8b37eda1396feeec3ab1c7ecee5eae31b -
Linux Linux 4.17 -

II. Public POCs for CVE-2026-23406

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III. Intelligence Information for CVE-2026-23406

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Same Patch Batch · Linux · 2026-04-01 · 11 CVEs total

CVE-2026-23411 7.8 HIGH apparmor: fix race between freeing data and fs accessing it
CVE-2026-23410 7.8 HIGH apparmor: fix race on rawdata dereference
CVE-2026-23408 7.8 HIGH apparmor: Fix double free of ns_name in aa_replace_profiles()
CVE-2026-23407 7.8 HIGH apparmor: fix missing bounds check on DEFAULT table in verify_dfa()
CVE-2026-23409 apparmor: fix differential encoding verification
CVE-2026-23405 apparmor: fix: limit the number of levels of policy namespaces
CVE-2026-23404 apparmor: replace recursive profile removal with iterative approach
CVE-2026-23403 apparmor: fix memory leak in verify_header
CVE-2026-23402 KVM: x86/mmu: Only WARN in direct MMUs when overwriting shadow-present SPTE
CVE-2026-23401 KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-23406

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