What is CVE-2026-23409?
In the Linux kernel, the following vulnerability has been resolved: apparmor: fix differential encoding verification Differential encoding allows loops to be created if it is abused. To prevent this the unpack should verify that a diff-encode chain terminates. Unfortunately the differential encode verification had two bugs. 1. it conflated states that had gone through check and already been marked, with states that were currently being checked and marked. This means that loops in the current chain being verified are treated as a chain that has already been verified. 2. the order bailout on already checked states compared current chain check iterators j,k instead of using the outer loop iterator i. Meaning a step backwards in states in the current chain verification was being mistaken for moving to an already verified state. Move to a double mark scheme where already verified states get a different mark, than the current chain being kept. This enables us to also drop the backwards verification check that was the cause of the second error as any already verified state is already marked.
1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 207 days ago.
Severity and exploitation probability
- EPSS (FIRST)
- 0.1% probability of exploitation in the next 30 days, higher than 6.6% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 0.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-04-01, last modified 2026-05-11
Is CVE-2026-23409 being exploited?
It currently carries a trending score of 7 in the Threadlinqs vulnerability feed.
Affected products and versions
- Linux: Linux
How to fix CVE-2026-23409
No vendor patch reference has been recorded for CVE-2026-23409 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.
Threat activity tracking CVE-2026-23409
1 tracked threat in the Threadlinqs corpus references CVE-2026-23409, either in the campaign’s CVE list or as an indicator on the campaign record.
Sources
Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories. Last verified by Threadlinqs on .
Other references
- git.kernel.org
- git.kernel.org (1439150cd3c411228b387ab5efca92199d2a659a)
- git.kernel.org (0fab44285445e9012674396d5c1236a67da518e0)
- git.kernel.org (f90e3ecd9e1ed69f1a370f866ceed1f104f3ab4a)
- git.kernel.org (34fc60b125ed1d4eb002c76b0664bf0619492167)
Showing 5 of 8 recorded references.