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Medium

Loop creation in Linux kernel AppArmor differential encoding verification

IdentifiersCVE-2026-23409CWE-835· Loop with Unreachable Exit…

CVE-2026-23409 is a Linux kernel vulnerability in AppArmor’s differential encoding verification logic during unpacking of differential-encoded data. Differential encoding chains are supposed to be verified to ensure they terminate, but the verification logic contained two bugs: it conflated states that had already been fully verified with states currently being traversed in the active verification chain, and it used the wrong iterator context when bailing out on previously checked states. As a result, malformed differential-encoded chains could evade proper loop detection and create non-terminating loops in the verification path. The fix changes the logic to use a double-mark scheme so states already verified are distinguished from states currently under verification, and removes the flawed backward-verification check.

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ANALYST BRIEF

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.

Successful exploitation can cause integrity and availability impact in the kernel context, primarily by triggering non-terminating loop conditions or related faulty processing in AppArmor’s differential encoding unpack/verification path. Published scoring indicates no confidentiality impact, but high availability impact and, in SUSE’s assessment, high integrity impact. NVD rates the issue CVSS v3.1 6.3 with vector AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H, indicating a local low-privilege denial-of-service condition is the primary demonstrated outcome.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce exposure by limiting local untrusted access to affected systems, especially low-privilege shell or container access that could reach the vulnerable kernel/AppArmor path. Restrict the ability to load or process untrusted AppArmor policy-related inputs where operationally feasible, and monitor for local denial-of-service symptoms involving hangs or abnormal kernel behavior. Mitigation is limited; kernel patching is the reliable fix.

Remediation

Patch, then assume compromise.

Apply a Linux kernel update that includes the AppArmor fix for differential encoding verification. The upstream remediation distinguishes already verified states from states in the current verification chain via a double-mark scheme and removes the incorrect backward-verification logic. Vendor advisories indicate fixes have been released across multiple SUSE and openSUSE kernel package lines; affected systems should be updated to the vendor-provided patched kernel and rebooted.
PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

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.

VendorProductType
LinuxLinux Kerneloperating_system

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

5 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

5 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

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Exposure mapping

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Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity2

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES
MITRE CVE
cve.org · CVE-2026-23409
NVD
nvd.nist.gov/vuln/detail/CVE-2026-23409
MITRE CWE · CWE-835
Loop with Unreachable Exit Condition…
Patch
git.kernel.org/stable/c/0fab44285445e9012674396d5c1236a67da518e0
Patch
git.kernel.org/stable/c/1439150cd3c411228b387ab5efca92199d2a659a
Patch
git.kernel.org/stable/c/1ff4857fac56ac5a90ee63b24db05fa5e91a45aa
Patch
git.kernel.org/stable/c/34fc60b125ed1d4eb002c76b0664bf0619492167
Patch
git.kernel.org/stable/c/39440b137546a3aa383cfdabc605fb73811b6093
Patch
git.kernel.org/stable/c/623a9d211bbbb031bb1cbdb38b23487648167f8a
Patch
git.kernel.org/stable/c/f90e3ecd9e1ed69f1a370f866ceed1f104f3ab4a
Patch
git.kernel.org/stable/c/ff7c73744fafe944ed9a7b2b7cf6c8d5557a3d84