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NVD / CVE Program· CNA Linux

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

Noroxi assessment

Priority: Monitor (action score 31/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.18% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 0510d1ba0976f97f521feb2b75b0572ea5df3ceb, 1fc94f16098213d01e56c97feed9b3ecf0147a37, 383b7270faf42564f133134c2fc3c24bbae52615; azl3 kernel 6.6.0.0-1 on Azure Linux 3.0 6.6.130.1-1; cbl2 kernel 5.15.202.1-1 on CBL-Mariner 2.0 Release Notes.

Low priority for now. Upgrade to Linux Linux 0510d1ba0976f97f521feb2b75b0572ea5df3ceb, 1fc94f16098213d01e56c97feed9b3ecf0147a37, 383b7270faf42564f133134c2fc3c24bbae52615; azl3 kernel 6.6.0.0-1 on Azure Linux 3.0 6.6.130.1-1; cbl2 kernel 5.15.202.1-1 on CBL-Mariner 2.0 Release Notes or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Apr 1, 2026
Updated
Aug 5, 2026
EPSS
0.1% · 8th percentile

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CNA vs NVD score

NVD
—
CNA · Linux
7.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

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When you'll hear from us

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  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel4.17.1 and later · before 5.10.253
  • linux linux kernel5.11 and later · before 5.15.203
  • linux linux kernel5.16 and later · before 6.1.169
  • linux linux kernel6.2 and later · before 6.6.130
  • linux linux kernel6.7 and later · before 6.12.77
  • linux linux kernel6.13 and later · before 6.18.18
  • linux linux kernel6.19 and later · before 6.19.8
  • linux linux kernel4.17
  • linux linux kernel7.0

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 4.17affected
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before c7dc56d8b37eda1396feeec3ab1c7ecee5eae31baffected · git
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before f16f2e5936c0f5f0d11fdf10d2be3e47e7108e42affected · git
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before 1fc94f16098213d01e56c97feed9b3ecf0147a37affected · git
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before 5a184f7cbdeaad17e16dedf3c17d0cd622edfed8affected · git
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before b73c1dff8a9d7eeaebabf8097a5b2de192f40913affected · git
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before 0510d1ba0976f97f521feb2b75b0572ea5df3cebaffected · git
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before 383b7270faf42564f133134c2fc3c24bbae52615affected · git
    • 074c1cd798cb0b481d7eaa749b64aa416563c053 and later · before 8756b68edae37ff546c02091989a4ceab3f20abdaffected · git
    • before 4.17not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.164-16.1.164-1
Debian:13linuxbefore 6.12.74-26.12.74-2
Debian:14linuxbefore 6.19.6-26.19.6-2
SUSE:Linux Enterprise Live Patching 15 SP6kernel-defaultbefore 6.4.0-150600.23.112.16.4.0-150600.23.112.1
SUSE:Linux Enterprise Live Patching 15 SP6kernel-livepatch-SLE15-SP6_Update_26before 1-150600.13.3.11-150600.13.3.1
SUSE:Linux Enterprise Server 15 SP6-LTSSkernel-64kbbefore 6.4.0-150600.23.112.16.4.0-150600.23.112.1
SUSE:Linux Enterprise Server 15 SP6-LTSSkernel-default-basebefore 6.4.0-150600.23.112.1.150600.12.52.16.4.0-150600.23.112.1.150600.12.52.1
SUSE:Linux Enterprise Server 15 SP6-LTSSkernel-docsbefore 6.4.0-150600.23.112.16.4.0-150600.23.112.1
SUSE:Linux Enterprise Server 15 SP6-LTSSkernel-obs-buildbefore 6.4.0-150600.23.112.16.4.0-150600.23.112.1
SUSE:Linux Enterprise Server 15 SP6-LTSSkernel-sourcebefore 6.4.0-150600.23.112.16.4.0-150600.23.112.1
SUSE:Linux Enterprise Server 15 SP6-LTSSkernel-symsbefore 6.4.0-150600.23.112.16.4.0-150600.23.112.1
SUSE:Linux Enterprise Server 15 SP6-LTSSkernel-zfcpdumpbefore 6.4.0-150600.23.112.16.4.0-150600.23.112.1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2026-23404Apr 1, 2026 · apparmor: replace recursive profile removal with iterative approach
    22Monitor
  • ← EarlierCVE-2026-23405Apr 1, 2026 · apparmor: fix: limit the number of levels of policy namespaces
    22Monitor
  • Later →CVE-2026-23407Apr 1, 2026 · apparmor: fix missing bounds check on DEFAULT table in verify_dfa()
    31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux0510d1ba0976f97f521feb2b75b0572ea5df3cebVendor (CNA)
Linux Linux1fc94f16098213d01e56c97feed9b3ecf0147a37Vendor (CNA)
Linux Linux383b7270faf42564f133134c2fc3c24bbae52615Vendor (CNA)
Linux Linux5a184f7cbdeaad17e16dedf3c17d0cd622edfed8Vendor (CNA)
Linux Linux8756b68edae37ff546c02091989a4ceab3f20abdVendor (CNA)
Linux Linuxb73c1dff8a9d7eeaebabf8097a5b2de192f40913Vendor (CNA)
Linux Linuxc7dc56d8b37eda1396feeec3ab1c7ecee5eae31bVendor (CNA)
Linux Linuxf16f2e5936c0f5f0d11fdf10d2be3e47e7108e42Vendor (CNA)
azl3 kernel 6.6.0.0-1 on Azure Linux 3.06.6.130.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 kernel 5.15.202.1-1 on CBL-Mariner 2.0Release NotesMicrosoft (MSRC)
debian:linux6.1.164-1 · Debian:12Package registry (OSV)
suse:kernel-64kb6.4.0-150600.23.112.1 · SUSE:Linux Enterprise Server 15 SP6-LTSSPackage registry (OSV)
suse:kernel-default6.4.0-150600.23.112.1 · SUSE:Linux Enterprise Live Patching 15 SP6Package registry (OSV)
suse:kernel-default-base6.4.0-150600.23.112.1.150600.12.52.1 · SUSE:Linux Enterprise Server 15 SP6-LTSSPackage registry (OSV)
suse:kernel-docs6.4.0-150600.23.112.1 · SUSE:Linux Enterprise Server 15 SP6-LTSSPackage registry (OSV)
suse:kernel-livepatch-SLE15-SP6_Update_261-150600.13.3.1 · SUSE:Linux Enterprise Live Patching 15 SP6Package registry (OSV)
suse:kernel-obs-build6.4.0-150600.23.112.1 · SUSE:Linux Enterprise Server 15 SP6-LTSSPackage registry (OSV)
suse:kernel-source6.4.0-150600.23.112.1 · SUSE:Linux Enterprise Server 15 SP6-LTSSPackage registry (OSV)
suse:kernel-syms6.4.0-150600.23.112.1 · SUSE:Linux Enterprise Server 15 SP6-LTSSPackage registry (OSV)
suse:kernel-zfcpdump6.4.0-150600.23.112.1 · SUSE:Linux Enterprise Server 15 SP6-LTSSPackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-125 · Out-of-bounds Read

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records