GHSA-7XF5-3QMR-J4C6

Vulnerability from github – Published: 2026-04-03 18:31 – Updated: 2026-04-03 18:31
VLAI?
Details

In the Linux kernel, the following vulnerability has been resolved:

nfsd: fix heap overflow in NFSv4.0 LOCK replay cache

The NFSv4.0 replay cache uses a fixed 112-byte inline buffer (rp_ibuf[NFSD4_REPLAY_ISIZE]) to store encoded operation responses. This size was calculated based on OPEN responses and does not account for LOCK denied responses, which include the conflicting lock owner as a variable-length field up to 1024 bytes (NFS4_OPAQUE_LIMIT).

When a LOCK operation is denied due to a conflict with an existing lock that has a large owner, nfsd4_encode_operation() copies the full encoded response into the undersized replay buffer via read_bytes_from_xdr_buf() with no bounds check. This results in a slab-out-of-bounds write of up to 944 bytes past the end of the buffer, corrupting adjacent heap memory.

This can be triggered remotely by an unauthenticated attacker with two cooperating NFSv4.0 clients: one sets a lock with a large owner string, then the other requests a conflicting lock to provoke the denial.

We could fix this by increasing NFSD4_REPLAY_ISIZE to allow for a full opaque, but that would increase the size of every stateowner, when most lockowners are not that large.

Instead, fix this by checking the encoded response length against NFSD4_REPLAY_ISIZE before copying into the replay buffer. If the response is too large, set rp_buflen to 0 to skip caching the replay payload. The status is still cached, and the client already received the correct response on the original request.

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{
  "affected": [],
  "aliases": [
    "CVE-2026-31402"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-04-03T16:16:39Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix heap overflow in NFSv4.0 LOCK replay cache\n\nThe NFSv4.0 replay cache uses a fixed 112-byte inline buffer\n(rp_ibuf[NFSD4_REPLAY_ISIZE]) to store encoded operation responses.\nThis size was calculated based on OPEN responses and does not account\nfor LOCK denied responses, which include the conflicting lock owner as\na variable-length field up to 1024 bytes (NFS4_OPAQUE_LIMIT).\n\nWhen a LOCK operation is denied due to a conflict with an existing lock\nthat has a large owner, nfsd4_encode_operation() copies the full encoded\nresponse into the undersized replay buffer via read_bytes_from_xdr_buf()\nwith no bounds check. This results in a slab-out-of-bounds write of up\nto 944 bytes past the end of the buffer, corrupting adjacent heap memory.\n\nThis can be triggered remotely by an unauthenticated attacker with two\ncooperating NFSv4.0 clients: one sets a lock with a large owner string,\nthen the other requests a conflicting lock to provoke the denial.\n\nWe could fix this by increasing NFSD4_REPLAY_ISIZE to allow for a full\nopaque, but that would increase the size of every stateowner, when most\nlockowners are not that large.\n\nInstead, fix this by checking the encoded response length against\nNFSD4_REPLAY_ISIZE before copying into the replay buffer. If the\nresponse is too large, set rp_buflen to 0 to skip caching the replay\npayload. The status is still cached, and the client already received the\ncorrect response on the original request.",
  "id": "GHSA-7xf5-3qmr-j4c6",
  "modified": "2026-04-03T18:31:23Z",
  "published": "2026-04-03T18:31:23Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31402"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0f0e2a54a31a7f9ad2915db99156114872317388"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/5133b61aaf437e5f25b1b396b14242a6bb0508e2"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8afb437ea1f70cacb4bbdf11771fb5c4d720b965"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ae8498337dfdfda71bdd0b807c9a23a126011d76"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c9452c0797c95cf2378170df96cf4f4b3bca7eff"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/dad0c3c0a8e5d1d6eb0fc455694ce3e25e6c57d0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}


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