Out-of-bounds read in Linux kernel AppArmor match_char() macro usage
CVE-2026-23406 is a Linux kernel AppArmor vulnerability caused by a side-effect bug in use of the match_char() macro during DFA traversal. The macro evaluates its character argument multiple times when traversing differential encoding chains. When the caller passes an expression with side effects such as *str++, the input pointer is incremented repeatedly inside the macro’s inner do-while loop rather than once per outer iteration. As a result, aa_dfa_match() may test different characters across iterations, skip input bytes, and advance the pointer beyond the end of the input buffer, leading to an out-of-bounds read. The issue was observed as a KASAN-reported slab-out-of-bounds read in aa_dfa_match() during AppArmor path permission checks triggered through file open processing. The upstream fix extracts the character value before invoking match_char(), ensuring single evaluation of the input character per outer loop.
Are you exposed to this one?
Mallory correlates every CVE against your assets, your vendors, and active adversary campaigns. Know which vulnerabilities matter for you, not just which ones are loud.
Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
If you can’t patch tonight, do this now.
Remediation
Patch, then assume compromise.
Exploits
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Affected products & vendors
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
Recent activity
4 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.
No news coverage yet. Advisories and community discussion only.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.