CVE-2026-23409 (GCVE-0-2026-23409)
Vulnerability from cvelistv5
Published
2026-04-01 08:36
Modified
2026-04-18 08:58
Severity ?
Summary
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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
Version: 031dcc8f4e84fea37dc6f78fdc7288aa7f8386c3
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\napparmor: fix differential encoding verification\n\nDifferential encoding allows loops to be created if it is abused. To\nprevent this the unpack should verify that a diff-encode chain\nterminates.\n\nUnfortunately the differential encode verification had two bugs.\n\n1. it conflated states that had gone through check and already been\n   marked, with states that were currently being checked and marked.\n   This means that loops in the current chain being verified are treated\n   as a chain that has already been verified.\n\n2. the order bailout on already checked states compared current chain\n   check iterators j,k instead of using the outer loop iterator i.\n   Meaning a step backwards in states in the current chain verification\n   was being mistaken for moving to an already verified state.\n\nMove to a double mark scheme where already verified states get a\ndifferent mark, than the current chain being kept. This enables us\nto also drop the backwards verification check that was the cause of\nthe second error as any already verified state is already marked."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-04-18T08:58:44.586Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
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          "url": "https://git.kernel.org/stable/c/ff7c73744fafe944ed9a7b2b7cf6c8d5557a3d84"
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        {
          "url": "https://git.kernel.org/stable/c/1439150cd3c411228b387ab5efca92199d2a659a"
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          "url": "https://git.kernel.org/stable/c/0fab44285445e9012674396d5c1236a67da518e0"
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          "url": "https://git.kernel.org/stable/c/f90e3ecd9e1ed69f1a370f866ceed1f104f3ab4a"
        },
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          "url": "https://git.kernel.org/stable/c/34fc60b125ed1d4eb002c76b0664bf0619492167"
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        },
        {
          "url": "https://git.kernel.org/stable/c/1ff4857fac56ac5a90ee63b24db05fa5e91a45aa"
        },
        {
          "url": "https://git.kernel.org/stable/c/39440b137546a3aa383cfdabc605fb73811b6093"
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      ],
      "title": "apparmor: fix differential encoding verification",
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-23409",
    "datePublished": "2026-04-01T08:36:38.516Z",
    "dateReserved": "2026-01-13T15:37:46.013Z",
    "dateUpdated": "2026-04-18T08:58:44.586Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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