CVE-2025-40205 (GCVE-0-2025-40205)
Vulnerability from cvelistv5
Published
2025-11-12 21:56
Modified
2026-08-05 12:08
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: btrfs: avoid potential out-of-bounds in btrfs_encode_fh() The function btrfs_encode_fh() does not properly account for the three cases it handles. Before writing to the file handle (fh), the function only returns to the user BTRFS_FID_SIZE_NON_CONNECTABLE (5 dwords, 20 bytes) or BTRFS_FID_SIZE_CONNECTABLE (8 dwords, 32 bytes). However, when a parent exists and the root ID of the parent and the inode are different, the function writes BTRFS_FID_SIZE_CONNECTABLE_ROOT (10 dwords, 40 bytes). If *max_len is not large enough, this write goes out of bounds because BTRFS_FID_SIZE_CONNECTABLE_ROOT is greater than BTRFS_FID_SIZE_CONNECTABLE originally returned. This results in an 8-byte out-of-bounds write at fid->parent_root_objectid = parent_root_id. A previous attempt to fix this issue was made but was lost. https://lore.kernel.org/all/4CADAEEC020000780001B32C@vpn.id2.novell.com/ Although this issue does not seem to be easily triggerable, it is a potential memory corruption bug that should be fixed. This patch resolves the issue by ensuring the function returns the appropriate size for all three cases and validates that *max_len is large enough before writing any data.
References
Impacted products
Vendor Product Version
Linux Linux Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
Version: be6e8dc0ba84029997075a1ec77b4ddb863cbe15
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/btrfs/export.c"
          ],
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          "vendor": "Linux",
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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": "2.6.29"
            },
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              "status": "unaffected",
              "version": "0",
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              "status": "unaffected",
              "version": "5.10.246",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "5.15.195",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "6.1.157",
              "versionType": "semver"
            },
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              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.113",
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              "status": "unaffected",
              "version": "6.12.54",
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              "version": "6.17.4",
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            },
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              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.18",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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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\nbtrfs: avoid potential out-of-bounds in btrfs_encode_fh()\n\nThe function btrfs_encode_fh() does not properly account for the three\ncases it handles.\n\nBefore writing to the file handle (fh), the function only returns to the\nuser BTRFS_FID_SIZE_NON_CONNECTABLE (5 dwords, 20 bytes) or\nBTRFS_FID_SIZE_CONNECTABLE (8 dwords, 32 bytes).\n\nHowever, when a parent exists and the root ID of the parent and the\ninode are different, the function writes BTRFS_FID_SIZE_CONNECTABLE_ROOT\n(10 dwords, 40 bytes).\n\nIf *max_len is not large enough, this write goes out of bounds because\nBTRFS_FID_SIZE_CONNECTABLE_ROOT is greater than\nBTRFS_FID_SIZE_CONNECTABLE originally returned.\n\nThis results in an 8-byte out-of-bounds write at\nfid-\u003eparent_root_objectid = parent_root_id.\n\nA previous attempt to fix this issue was made but was lost.\n\nhttps://lore.kernel.org/all/4CADAEEC020000780001B32C@vpn.id2.novell.com/\n\nAlthough this issue does not seem to be easily triggerable, it is a\npotential memory corruption bug that should be fixed. This patch\nresolves the issue by ensuring the function returns the appropriate size\nfor all three cases and validates that *max_len is large enough before\nwriting any data."
        }
      ],
      "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 primary trigger is the local `name_to_handle_at(AT_HANDLE_CONNECTABLE)` syscall on a mounted btrfs filesystem, where the caller fully controls the destination buffer size. The nfsd path can also reach the encoder remotely, but only with the non-default `subtree_check` export option, so local is the representative vector.\nAC:L - An unprivileged attacker deterministically controls every element they can influence \u2014 the btrfs mount, the target inode, the `AT_HANDLE_CONNECTABLE` flag, and the undersized `handle_bytes` value (8-9 dwords) that makes the 40-byte write overflow \u2014 with no race or memory-layout grooming required.\nPR:L - `name_to_handle_at()` requires no capability (unlike `open_by_handle_at()`, which needs CAP_DAC_READ_SEARCH), so any local unprivileged user with read access to a btrfs mount can invoke the vulnerable encoder. Creating btrfs subvolumes is likewise permitted to unprivileged users with write access to the parent directory.\nUI:N - The attacker triggers the overflow entirely through their own syscall on an already-mounted filesystem; no victim action, no crafted image mount, and no administrator involvement is needed.\nS:U - The out-of-bounds write corrupts kernel heap memory within the same kernel security authority, with no crossing of a VM, IOMMU, or sandbox boundary.\nC:H - An 8-byte heap out-of-bounds write is a memory-corruption primitive that can be leveraged to overwrite adjacent kernel objects (e.g. length or pointer fields) and thereby obtain arbitrary kernel-memory disclosure.\nI:H - This is a direct out-of-bounds write of a 64-bit value (`parent_root_objectid`) past the end of a kernel allocation, and per CVSS kernel guidance an OOB write is rated High for integrity due to its potential for control-flow hijacking.\nA:H - Corrupting adjacent kernel heap metadata or object state leads to oops, BUG, or panic, and the write is detectable/fatal under KASAN or hardened allocators, causing a full denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:08:34.187Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/60de2f55d2aca53e81b4ef2a67d7cc9e1eb677db"
        },
        {
          "url": "https://git.kernel.org/stable/c/742b44342204e5dfe3926433823623c1a0c581df"
        },
        {
          "url": "https://git.kernel.org/stable/c/d3a9a8e1275eb9b87f006b5562a287aea3f6885f"
        },
        {
          "url": "https://git.kernel.org/stable/c/d91f6626133698362bba08fbc04bd72c466806d3"
        },
        {
          "url": "https://git.kernel.org/stable/c/0276c8582488022f057b4cec21975a5edf079f47"
        },
        {
          "url": "https://git.kernel.org/stable/c/361d67276eb8ec6be8f27f4ad6c6090459438fee"
        },
        {
          "url": "https://git.kernel.org/stable/c/43143776b0a7604d873d1a6f3e552a00aa930224"
        },
        {
          "url": "https://git.kernel.org/stable/c/dff4f9ff5d7f289e4545cc936362e01ed3252742"
        }
      ],
      "title": "btrfs: avoid potential out-of-bounds in btrfs_encode_fh()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-40205",
    "datePublished": "2025-11-12T21:56:35.403Z",
    "dateReserved": "2025-04-16T07:20:57.179Z",
    "dateUpdated": "2026-08-05T12:08:34.187Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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