audit: fix out-of-bounds read in audit_compare_dname_path()

{
  "id": "e07087fd71b8ccea34c829e5f3fdc40fce8ac9ba0f949846658e5f115a6480f8",
  "url": "https://osv.dev/vulnerability/CVE-2025-39840",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "audit: fix out-of-bounds read in audit_compare_dname_path()",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: audit: fix out-of-bounds read in audit_compare_dname_path() When a watch on dir=/ is combined with an fsnotify event for a single-character name directly under / (e.g., creating /a), an out-of-bounds read can occur in audit_compare_dname_path(). The helper parent_len() returns 1 for \"/\". In audit_compare_dname_path(), when parentlen equals the full path length (1), the code sets p = path + 1 and pathlen = 1 - 1 = 0. The subsequent loop then dereferences p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read. Fix this by adding a pathlen > 0 check to the while loop condition to prevent the out-of-bounds access. [PM: subject tweak, sign-off email fixes]",
    "evidence": "osv:CVE-2025-39840",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.16.6",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "high",
    "structured": {
      "id": "CVE-2025-39840",
      "aliases": [
        "CVE-2025-39840"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e92eebb0d6116f942ab25dfb1a41905aa59472a8"
                },
                {
                  "fixed": "9735a9dcc307427e7d6336c54171682f1bac9789"
                },
                {
                  "fixed": "4540f1d23e7f387880ce46d11b5cd3f27248bf8d"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39840.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "6.14.0"
                },
                {
                  "fixed": "6.16.6"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2025-39840.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:33.830448311Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/4540f1d23e7f387880ce46d11b5cd3f27248bf8d",
        "https://git.kernel.org/stable/c/9735a9dcc307427e7d6336c54171682f1bac9789",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39840.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2025-39840",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/39xxx/CVE-2025-39840.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2025-39840",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 501147,
  "published_at": "2025-09-19T15:26:15.596+00:00"
}