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CVE-2026-23409— apparmor: fix differential encoding verification

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于差分编码验证存在缺陷，可能导致循环创建。

AI Predicted 5.3 Difficulty: Hard EPSS 0.18% · P7

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< ff7c73744fafe944ed9a7b2b7cf6c8d5557a3d84 affected
031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< 1439150cd3c411228b387ab5efca92199d2a659a affected
031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< 0fab44285445e9012674396d5c1236a67da518e0 affected
031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< f90e3ecd9e1ed69f1a370f866ceed1f104f3ab4a affected
031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< 34fc60b125ed1d4eb002c76b0664bf0619492167 affected
031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< 623a9d211bbbb031bb1cbdb38b23487648167f8a affected
031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< 1ff4857fac56ac5a90ee63b24db05fa5e91a45aa affected
031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3< 39440b137546a3aa383cfdabc605fb73811b6093 affected
… +10 more rows
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I. Basic Information for CVE-2026-23409

Vulnerability Information
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Vulnerability Title
apparmor: fix differential encoding verification
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会的开源操作系统Linux所使用的内核。 Linux kernel存在安全漏洞，该漏洞源于差分编码验证存在缺陷，可能导致循环创建。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3 ~ ff7c73744fafe944ed9a7b2b7cf6c8d5557a3d84 -
Linux Linux 4.17 -

II. Public POCs for CVE-2026-23409

# POC Description Source Link Shenlong Link
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III. Intelligence Information for CVE-2026-23409

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Same Patch Batch · Linux · 2026-04-01 · 11 CVEs total

CVE-2026-23411 7.8 HIGH apparmor: fix race between freeing data and fs accessing it
CVE-2026-23410 7.8 HIGH apparmor: fix race on rawdata dereference
CVE-2026-23408 7.8 HIGH apparmor: Fix double free of ns_name in aa_replace_profiles()
CVE-2026-23407 7.8 HIGH apparmor: fix missing bounds check on DEFAULT table in verify_dfa()
CVE-2026-23406 7.8 HIGH apparmor: fix side-effect bug in match_char() macro usage
CVE-2026-23405 apparmor: fix: limit the number of levels of policy namespaces
CVE-2026-23404 apparmor: replace recursive profile removal with iterative approach
CVE-2026-23403 apparmor: fix memory leak in verify_header
CVE-2026-23402 KVM: x86/mmu: Only WARN in direct MMUs when overwriting shadow-present SPTE
CVE-2026-23401 KVM: x86/mmu: Drop/zap existing present SPTE even when creating an MMIO SPTE

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-23409

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