CVE-2026-63952 (GCVE-0-2026-63952)
Vulnerability from cvelistv5
Published
2026-07-19 14:55
Modified
2026-08-05 12:37
Severity ?
8.4 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
Summary
In the Linux kernel, the following vulnerability has been resolved: memfd: deny writeable mappings when implying SEAL_WRITE When SEAL_EXEC is added, SEAL_WRITE is implied to make W^X. But the implied seal is set after the check that makes sure the memfd can not have any writable mappings. This means one can use SEAL_EXEC to apply SEAL_WRITE while having writeable mappings. This breaks the contract that SEAL_WRITE provides and can be used by an attacker to pass a memfd that appears to be write sealed but can still be modified arbitrarily. Fix this by adding the implied seals before the call for mapping_deny_writable() is done.
References
Impacted products
Vendor Product Version
Linux Linux Version: c4f75bc8bd6b3d62665e1f5400c419540edb5601
Version: c4f75bc8bd6b3d62665e1f5400c419540edb5601
Version: c4f75bc8bd6b3d62665e1f5400c419540edb5601
Version: c4f75bc8bd6b3d62665e1f5400c419540edb5601
Version: c4f75bc8bd6b3d62665e1f5400c419540edb5601
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "mm/memfd.c"
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          ],
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          "vendor": "Linux",
          "versions": [
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              "version": "0",
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              "status": "unaffected",
              "version": "6.18.35",
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              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.143",
                  "versionStartIncluding": "6.3",
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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\nmemfd: deny writeable mappings when implying SEAL_WRITE\n\nWhen SEAL_EXEC is added, SEAL_WRITE is implied to make W^X.  But the\nimplied seal is set after the check that makes sure the memfd can not have\nany writable mappings.  This means one can use SEAL_EXEC to apply\nSEAL_WRITE while having writeable mappings.\n\nThis breaks the contract that SEAL_WRITE provides and can be used by an\nattacker to pass a memfd that appears to be write sealed but can still be\nmodified arbitrarily.\n\nFix this by adding the implied seals before the call for\nmapping_deny_writable() is done."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.4,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - Exploitation requires local syscalls (memfd_create, mmap, fcntl) with no network-facing code path; the vulnerable logic is reached only through the local fcntl(F_ADD_SEALS) interface on a memfd file descriptor.\nAC:L - The attack is a reliable, deterministic syscall sequence (create executable memfd, establish a writable MAP_SHARED mapping, then apply F_SEAL_EXEC) with no race or attacker-uncontrollable conditions.\nPR:L - Any unprivileged local user can invoke memfd_create, mmap, and fcntl without capabilities; these interfaces are available inside unprivileged user namespaces with no real-root requirement.\nUI:N - Exploitation does not require a human victim action; in the highest-impact scenario a sandboxed process programmatically passes the sealed-appearing memfd to a trusting peer via IPC (e.g., SCM_RIGHTS) without user interaction.\nS:C - The bug breaks the memfd seal security contract designed for mutually untrusted parties, allowing a malicious local peer to deceive a separate process that relies on F_SEAL_WRITE immutability, crossing the inter-process trust boundary (sandbox/W^X enforcement).\nC:H - Bypassing write-seal/W^X guarantees enables arbitrary modification of executable memfd contents presented as immutable, which can be leveraged for arbitrary code execution in a trusting victim process and thereby full read of that process\u0027s memory.\nI:H - The vulnerability allows arbitrary modification of memory that is advertised as write-sealed (F_SEAL_WRITE), defeating the kernel\u0027s immutability guarantee and enabling W^X bypass and code injection into trusted execution contexts.\nA:N - The flaw is a logic error in seal enforcement that does not cause kernel crashes, panics, hangs, or denial of service; exploitation maintains availability while subverting integrity guarantees."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:37:37.398Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/b3f4f82d1315f1439059a83d1c22c51a5b43d99e"
        },
        {
          "url": "https://git.kernel.org/stable/c/3be2a24f7f72ad7321ed6ad1715b956a4527bcf4"
        },
        {
          "url": "https://git.kernel.org/stable/c/0995d1f79aed8ccbf62056189dd53fd19726ea08"
        },
        {
          "url": "https://git.kernel.org/stable/c/555702282d4536a865dfffb1cd4f6028f196e7e8"
        },
        {
          "url": "https://git.kernel.org/stable/c/3b041514cb6eae45869b020f743c14d983363222"
        }
      ],
      "title": "memfd: deny writeable mappings when implying SEAL_WRITE",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63952",
    "datePublished": "2026-07-19T14:55:44.809Z",
    "dateReserved": "2026-07-19T07:54:57.023Z",
    "dateUpdated": "2026-08-05T12:37:37.398Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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