CVE-2025-21836 (GCVE-0-2025-21836)
Vulnerability from cvelistv5
Published
2025-03-07 09:09
Modified
2026-08-05 11:54
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: io_uring/kbuf: reallocate buf lists on upgrade IORING_REGISTER_PBUF_RING can reuse an old struct io_buffer_list if it was created for legacy selected buffer and has been emptied. It violates the requirement that most of the field should stay stable after publish. Always reallocate it instead.
References
Impacted products
Vendor Product Version
Linux Linux Version: 2fcabce2d7d34f69a888146dab15b36a917f09d4
Version: 2fcabce2d7d34f69a888146dab15b36a917f09d4
Version: 2fcabce2d7d34f69a888146dab15b36a917f09d4
Version: 2fcabce2d7d34f69a888146dab15b36a917f09d4
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "io_uring/kbuf.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "io_uring/kbuf.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.19"
            },
            {
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.79",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.16",
              "versionType": "semver"
            },
            {
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              "status": "unaffected",
              "version": "6.13.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.14",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.79",
                  "versionStartIncluding": "5.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.16",
                  "versionStartIncluding": "5.19",
                  "vulnerable": true
                },
                {
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                  "vulnerable": true
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                {
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                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nio_uring/kbuf: reallocate buf lists on upgrade\n\nIORING_REGISTER_PBUF_RING can reuse an old struct io_buffer_list if it\nwas created for legacy selected buffer and has been emptied. It violates\nthe requirement that most of the field should stay stable after publish.\nAlways reallocate it instead."
        }
      ],
      "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 - The vulnerable code is reached only through the io_uring_setup/io_uring_register syscalls; there is no network or adjacent path, so exploitation requires local access to issue syscalls.\nAC:L - The attacker performs every step themselves (create a legacy buffer group, empty it, upgrade the same bgid via PBUF_RING, then mmap), controlling both sides of any race; the trigger is fully deterministic and reliable.\nPR:L - io_uring is available to unprivileged users by default (kernel.io_uring_disabled=0) and provided-buffer registration needs no capability, so only a basic local user account is required.\nUI:N - The entire sequence is driven by the attacking process; no action by any other user or victim is needed.\nS:U - The corruption is confined to the kernel\u0027s own security authority (standard local privilege escalation) and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - The type confusion / use-after-free of the io_buffer_list and the retained user mapping to freed kernel pages give the attacker read access to reallocated kernel memory, enabling arbitrary kernel information disclosure.\nI:H - The same UAF and shared-page primitive give write access to freed/reallocated kernel memory, exploitable for arbitrary kernel write and privilege escalation as demonstrated for this io_uring buffer-ring bug class.\nA:H - At minimum the type confusion and use-after-free corrupt kernel structures, causing an oops/panic and denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:54:49.695Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/146a185f6c05ee263db715f860620606303c4633"
        },
        {
          "url": "https://git.kernel.org/stable/c/7d0dc28dae836caf7645fef62a10befc624dd17b"
        },
        {
          "url": "https://git.kernel.org/stable/c/2a5febbef40ce968e295a7aeaa5d5cbd9e3e5ad4"
        },
        {
          "url": "https://git.kernel.org/stable/c/8802766324e1f5d414a81ac43365c20142e85603"
        },
        {
          "url": "https://u1f383.github.io/slides/talks/2025_Hexacon-Deja_Vu_in_Linux_io_uring_Breaking_Memory_Sharing_Again_After_Generations_of_Fixes.pdf"
        }
      ],
      "title": "io_uring/kbuf: reallocate buf lists on upgrade",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21836",
    "datePublished": "2025-03-07T09:09:56.127Z",
    "dateReserved": "2024-12-29T08:45:45.777Z",
    "dateUpdated": "2026-08-05T11:54:49.695Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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