CVE-2026-89761 (GCVE-0-2026-89761)
Vulnerability from cvelistv5
Published
2026-09-11 19:47
Modified
2026-10-21 12:48
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: apparmor: fix out-of-bounds write when null terminating a label vec aa_vec_unique() null terminates at vec[n - dups] when VEC_FLAG_TERMINATE is passed. If the components are all distinct no duplicates are dropped, dups is 0 and the terminator goes to vec[n], so the caller has to provide room for n + 1 entries. aa_label_strn_parse() sets up its vector with vec_setup(profile, vec, len, gfp) and then calls aa_vec_unique(vec, len, VEC_FLAG_TERMINATE), but vec_setup() does not reserve the terminator entry. Up to LOCAL_VEC_ENTRIES it uses the local array of LOCAL_VEC_ENTRIES pointers, above that it allocates exactly len pointers. The terminator therefore lands one entry past the end of the local array when len is LOCAL_VEC_ENTRIES, and one entry past the end of the allocation when len is larger. len comes from the number of "//&" separated components in the label name and label_count_strn_entries() does not bound it. An unprivileged task reaches the parse by writing to /proc/self/attr/apparmor/current or through lsm_set_self_attr(2), both of which go through do_setattr(), and the name is parsed before the change_profile permission is checked. The query_label() path behind the securityfs .access file, which is mode 0666, performs no permission check at all. Every component has to resolve to a loaded profile, so a system with policy loaded is required. The other two VEC_FLAG_TERMINATE users work on a label vec that aa_label_alloc() has already sized with "+ 1 for null terminator entry on vec". Reserve the same entry in vec_setup() and DEFINE_VEC(). Passing len + 1 from the caller instead would move len == LOCAL_VEC_ENTRIES out of the local array and into kzalloc().
References
Impacted products
Vendor Product Version
Linux Linux Version: f1bd904175e8190ce14aedee37e207ab51fe3b30
Version: f1bd904175e8190ce14aedee37e207ab51fe3b30
Version: f1bd904175e8190ce14aedee37e207ab51fe3b30
Version: f1bd904175e8190ce14aedee37e207ab51fe3b30
Version: f1bd904175e8190ce14aedee37e207ab51fe3b30
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{
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          "programFiles": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\napparmor: fix out-of-bounds write when null terminating a label vec\n\naa_vec_unique() null terminates at vec[n - dups] when VEC_FLAG_TERMINATE\nis passed. If the components are all distinct no duplicates are dropped,\ndups is 0 and the terminator goes to vec[n], so the caller has to provide\nroom for n + 1 entries.\n\naa_label_strn_parse() sets up its vector with vec_setup(profile, vec, len,\ngfp) and then calls aa_vec_unique(vec, len, VEC_FLAG_TERMINATE), but\nvec_setup() does not reserve the terminator entry. Up to LOCAL_VEC_ENTRIES\nit uses the local array of LOCAL_VEC_ENTRIES pointers, above that it\nallocates exactly len pointers. The terminator therefore lands one entry\npast the end of the local array when len is LOCAL_VEC_ENTRIES, and one\nentry past the end of the allocation when len is larger.\n\nlen comes from the number of \"//\u0026\" separated components in the label name\nand label_count_strn_entries() does not bound it. An unprivileged task\nreaches the parse by writing to /proc/self/attr/apparmor/current or through\nlsm_set_self_attr(2), both of which go through do_setattr(), and the name\nis parsed before the change_profile permission is checked.\nThe query_label() path behind the securityfs .access file, which is\nmode 0666, performs no permission check at all. Every component has to\nresolve to a loaded profile, so a system with policy loaded is required.\n\nThe other two VEC_FLAG_TERMINATE users work on a label vec that\naa_label_alloc() has already sized with \"+ 1 for null terminator entry on\nvec\". Reserve the same entry in vec_setup() and DEFINE_VEC(). Passing\nlen + 1 from the caller instead would move len == LOCAL_VEC_ENTRIES out of\nthe local array and into kzalloc()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - An unprivileged local process reaches aa_label_strn_parse() by writing a compound label to /sys/kernel/security/apparmor/.access (mode 0666) via query_label()/query_data(), or via /proc/self/attr/apparmor/current and lsm_set_self_attr(2) through do_setattr(); there is no network-facing path.\nAC:L - The attacker fully controls the \"//\u0026\"-separated label string and thus the vector length; when at least eight distinct profiles are loaded (typical Ubuntu/Debian/SUSE policy, or attacker-loaded via user namespaces) with no duplicates, aa_vec_unique() deterministically writes NULL one pointer past the stack array or heap allocation, with no race.\nPR:L - query_label() on the world-writable .access file performs no capability or change_profile check, and do_setattr() parses the name before AA_MAY_CHANGE_PROFILE is tested, so a basic unprivileged local user suffices; real root is not required.\nUI:N - The attacker opens and writes the .access query or their own procattr themselves; no victim action such as mounting a filesystem or opening a file is required.\nS:U - The out-of-bounds write corrupts kernel stack or heap within the same kernel security authority. This is standard local privilege-escalation impact, not a VM escape or IOMMU/sandbox boundary crossing.\nC:H - The one-pointer out-of-bounds write lands in adjacent stack locals or the next kmalloc object. With attacker-chosen allocation size (component count) for heap grooming, that corruption can be leveraged as a kernel memory-disclosure primitive, so confidentiality impact is high.\nI:H - aa_vec_unique() writes a NULL pointer one slot past a LOCAL_VEC_ENTRIES stack array or a heap buffer sized exactly to the attacker-chosen component count. An out-of-bounds write that corrupts adjacent kernel objects is a write primitive suitable for control-flow hijacking.\nA:H - Corrupting an adjacent stack pointer, heap object, or stack canary can oops, panic, or hang the kernel; the unexploited NULL write alone is sufficient for denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-21T12:48:38.023Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/b17c8f5dcb36a032688847b2bce4bd813b4baad1"
        },
        {
          "url": "https://git.kernel.org/stable/c/9124e078ea2250d8d01d2162a550acb01ef5bf48"
        },
        {
          "url": "https://git.kernel.org/stable/c/28069434aef66b9d084f0609b7a29c171846815e"
        },
        {
          "url": "https://git.kernel.org/stable/c/36bdd0b45ec3f4822832a56e9db8674c8450dfce"
        },
        {
          "url": "https://git.kernel.org/stable/c/9f1e40193eef7f047e6b77cfb4b4cafdecd7a123"
        }
      ],
      "title": "apparmor: fix out-of-bounds write when null terminating a label vec",
      "x_generator": {
        "engine": "bippy-1.2.0"
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  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89761",
    "datePublished": "2026-09-11T19:47:02.837Z",
    "dateReserved": "2026-09-11T19:38:34.764Z",
    "dateUpdated": "2026-10-21T12:48:38.023Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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