Linux Kernel AppArmor diff-encoding verification flaw
CVE-2026-23409 Published on April 1, 2026
apparmor: fix differential encoding verification
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.
Products Associated with CVE-2026-23409
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Affected Versions
Linux:- Version 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3 and below f90e3ecd9e1ed69f1a370f866ceed1f104f3ab4a is affected.
- Version 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3 and below 34fc60b125ed1d4eb002c76b0664bf0619492167 is affected.
- Version 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3 and below 623a9d211bbbb031bb1cbdb38b23487648167f8a is affected.
- Version 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3 and below 1ff4857fac56ac5a90ee63b24db05fa5e91a45aa is affected.
- Version 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3 and below 39440b137546a3aa383cfdabc605fb73811b6093 is affected.
- Version 4.17 is affected.
- Before 4.17 is unaffected.
- Version 6.6.130, <= 6.6.* is unaffected.
- Version 6.12.77, <= 6.12.* is unaffected.
- Version 6.18.18, <= 6.18.* is unaffected.
- Version 6.19.8, <= 6.19.* is unaffected.
- Version 7.0-rc4, <= * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.