{"id":"CVE-2026-31402","summary":"nfsd: fix heap overflow in NFSv4.0 LOCK replay cache","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.","modified":"2026-04-28T04:12:41.093986Z","published":"2026-04-03T15:16:05.724Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31402.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"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"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f9fcb4441f6c02bb20c2eb340101e27dfe23607c"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31402.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-31402"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"1da177e4c3f41524e886b7f1b8a0c1fc7321cac2"},{"fixed":"f9fcb4441f6c02bb20c2eb340101e27dfe23607c"},{"fixed":"c9452c0797c95cf2378170df96cf4f4b3bca7eff"},{"fixed":"8afb437ea1f70cacb4bbdf11771fb5c4d720b965"},{"fixed":"dad0c3c0a8e5d1d6eb0fc455694ce3e25e6c57d0"},{"fixed":"0f0e2a54a31a7f9ad2915db99156114872317388"},{"fixed":"ae8498337dfdfda71bdd0b807c9a23a126011d76"},{"fixed":"5133b61aaf437e5f25b1b396b14242a6bb0508e2"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31402.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"2.6.12"},{"fixed":"5.10.253"}]},{"type":"ECOSYSTEM","events":[{"introduced":"5.11.0"},{"fixed":"6.1.167"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.2.0"},{"fixed":"6.6.130"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.78"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.20"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"6.19.10"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-31402.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"}]}