{"cve":"CVE-2026-31402","nvd":{"published":"2026-04-03T16:16:39.283","modified":"2026-10-19T19:17:51.350","status":"Modified","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","score":9.8},"cwes":["CWE-787","CWE-122"],"references":["https://git.kernel.org/stable/c/0f0e2a54a31a7f9ad2915db99156114872317388","https://git.kernel.org/stable/c/2665887a69437a8a4f552f69509eecfb73d4aa19","https://git.kernel.org/stable/c/5133b61aaf437e5f25b1b396b14242a6bb0508e2","https://git.kernel.org/stable/c/8afb437ea1f70cacb4bbdf11771fb5c4d720b965","https://git.kernel.org/stable/c/ae8498337dfdfda71bdd0b807c9a23a126011d76"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2026-31402","score":0.01198,"percentile":0.67908,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}