CVE-2026-64298 (GCVE-0-2026-64298)
Vulnerability from cvelistv5
Published
2026-07-25 08:49
Modified
2026-08-17 04:52
Severity ?
7.1 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: NFSv4: include MAY_WRITE in open permission mask for O_TRUNC POSIX requires write permission to truncate a file, so an open() that specifies O_TRUNC must be authorized for write access regardless of the O_ACCMODE access mode. nfs_open_permission_mask() builds the access mask passed to nfs_may_open(), which is the local authorization gate for OPENs the client serves itself from a cached write delegation via the can_open_delegated() path in nfs4_try_open_cached(). The mask is derived from O_ACCMODE alone, so an open(O_RDONLY | O_TRUNC) against a file the caller cannot write requests only MAY_READ and passes the local check. The OPEN is then satisfied locally and the truncation is issued to the server as a SETATTR(size=0) over the delegation stateid, which the server accepts under standard write-delegation semantics. POSIX requires that this open fail with EACCES. Include MAY_WRITE in the mask whenever O_TRUNC is set so the local check matches the access the server would have enforced.
References
Impacted products
Vendor Product Version
Linux Linux Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
Version: af22f94ae02ab9dd4fd7fe628c8434a59cc293be
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nfs/dir.c"
          ],
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "version": "2.6.24"
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              "status": "unaffected",
              "version": "0",
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              "version": "5.10.261",
              "versionType": "semver"
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              "version": "5.15.212",
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              "status": "unaffected",
              "version": "6.1.178",
              "versionType": "semver"
            },
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            },
            {
              "lessThanOrEqual": "6.12.*",
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              "version": "6.12.96",
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            },
            {
              "lessThanOrEqual": "6.18.*",
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            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "vulnerable": true
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                  "vulnerable": true
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              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSv4: include MAY_WRITE in open permission mask for O_TRUNC\n\nPOSIX requires write permission to truncate a file, so an open() that\nspecifies O_TRUNC must be authorized for write access regardless of the\nO_ACCMODE access mode.\n\nnfs_open_permission_mask() builds the access mask passed to\nnfs_may_open(), which is the local authorization gate for OPENs the\nclient serves itself from a cached write delegation via the\ncan_open_delegated() path in nfs4_try_open_cached().  The mask is\nderived from O_ACCMODE alone, so an open(O_RDONLY | O_TRUNC) against a\nfile the caller cannot write requests only MAY_READ and passes the\nlocal check.  The OPEN is then satisfied locally and the truncation is\nissued to the server as a SETATTR(size=0) over the delegation stateid,\nwhich the server accepts under standard write-delegation semantics.\nPOSIX requires that this open fail with EACCES.\n\nInclude MAY_WRITE in the mask whenever O_TRUNC is set so the local\ncheck matches the access the server would have enforced."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - An unprivileged local process triggers the flaw through open/openat with O_RDONLY|O_TRUNC on an accessible NFSv4-mounted file. The resulting NFS RPC is outbound and does not make the attack remotely reachable.\nAC:L - Once the client holds a standard cached write delegation, a single deterministic open triggers the unauthorized truncation without a race or timing requirement. Delegations persist and the attacker can repeatedly target files actively written through the same client.\nPR:L - The attacker needs only ordinary local access and read/search permission for the target path; no capability or administrative privilege is required. User namespaces are unnecessary.\nUI:N - The attacker invokes open directly and no contemporaneous action by another user is required.\nS:U - The faulty client-side permission check and modification of the delegated NFS file remain within the NFS filesystem access-control authority.\nC:N - The flaw discloses no kernel or file data beyond content the caller was already authorized to read, and it involves no memory corruption.\nI:H - The attacker can irreversibly truncate the complete contents of a file for which write access was denied, causing total integrity loss of that resource.\nA:H - Truncating critical NFS-hosted executables, configuration, databases, or operational data can completely disable dependent systems or services, and the attack can be repeated against additional delegated files."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:52:55.989Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/4817c8974315b666e895b7d1bb83cd3664c323b1"
        },
        {
          "url": "https://git.kernel.org/stable/c/cb148a2762d644bff1894728e8835a9a4b84f9ea"
        },
        {
          "url": "https://git.kernel.org/stable/c/30fdf4df6c3c00efec947e4ddf97f0fdd4473628"
        },
        {
          "url": "https://git.kernel.org/stable/c/22c1fd1355ad4ca27aa7f0fa02719122dd92d9de"
        },
        {
          "url": "https://git.kernel.org/stable/c/6bd7d0a06b53c4e797e1a9cea0d2d41aa1b26230"
        },
        {
          "url": "https://git.kernel.org/stable/c/a937e92c1d00534b5c2e3e9f4381b7e988180797"
        },
        {
          "url": "https://git.kernel.org/stable/c/e36501b7d4abdcd6d69a7cb901b2f286b7a3d041"
        },
        {
          "url": "https://git.kernel.org/stable/c/5140f099ecd8a2f2808b7f7b720ee1bad8468974"
        }
      ],
      "title": "NFSv4: include MAY_WRITE in open permission mask for O_TRUNC",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64298",
    "datePublished": "2026-07-25T08:49:35.101Z",
    "dateReserved": "2026-07-19T15:36:31.778Z",
    "dateUpdated": "2026-08-17T04:52:55.989Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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