{"id":"CVE-2021-47506","state":"PUBLISHED","title":"nfsd: fix use-after-free due to delegation race","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix use-after-free due to delegation race\n\nA delegation break could arrive as soon as we've called vfs_setlease.  A\ndelegation break runs a callback which immediately (in\nnfsd4_cb_recall_prepare) adds the delegation to del_recall_lru.  If we\nthen exit nfs4_set_delegation without hashing the delegation, it will be\nfreed as soon as the callback is done with it, without ever being\nremoved from del_recall_lru.\n\nSymptoms show up later as use-after-free or list corruption warnings,\nusually in the laundromat thread.\n\nI suspect aba2072f4523 \"nfsd: grant read delegations to clients holding\nwrites\" made this bug easier to hit, but I looked as far back as v3.0\nand it looks to me it already had the same problem.  So I'm not sure\nwhere the bug was introduced; it may have been there from the beginning.","publishedAt":"2024-05-24T15:01:52.746Z","updatedAt":"2026-08-05T08:48:10.240Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"04a8d07f3d58308b92630045560799a3faa3ebce","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"348714018139c39533c55661a0c7c990671396b4","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"33645d3e22720cac1e4548f8fef57bf0649536ee","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"2becaa990b93cbd2928292c0b669d3abb6cf06d4","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"e0759696de6851d7536efddfdd2dfed4c4df1f09","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"eeb0711801f5e19ef654371b627682aed3b11373","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"148c816f10fd11df27ca6a9b3238cdd42fa72cd3","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"548ec0805c399c65ed66c6641be467f717833ab5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4state.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.17","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.17","versionType":"semver"},{"version":"4.4.296","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.294","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.259","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.222","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.168","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.85","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.8","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"5.16","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4state.c"]}],"references":["https://git.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebce","https://git.kernel.org/stable/c/348714018139c39533c55661a0c7c990671396b4","https://git.kernel.org/stable/c/33645d3e22720cac1e4548f8fef57bf0649536ee","https://git.kernel.org/stable/c/2becaa990b93cbd2928292c0b669d3abb6cf06d4","https://git.kernel.org/stable/c/e0759696de6851d7536efddfdd2dfed4c4df1f09","https://git.kernel.org/stable/c/eeb0711801f5e19ef654371b627682aed3b11373","https://git.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3","https://git.kernel.org/stable/c/548ec0805c399c65ed66c6641be467f717833ab5"],"weaknesses":[],"ingestedAt":"2026-10-29T19:49:19.404Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2021/47xxx/CVE-2021-47506.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47506","state":"PUBLISHED","datePublished":"2024-05-24T15:01:52.746Z","dateUpdated":"2026-08-05T08:48:10.240Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2024-05-22T06:20:56.205Z"},"containers":{"cna":{"title":"nfsd: fix use-after-free due to delegation race","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix use-after-free due to delegation race\n\nA delegation break could arrive as soon as we've called vfs_setlease.  A\ndelegation break runs a callback which immediately (in\nnfsd4_cb_recall_prepare) adds the delegation to del_recall_lru.  If we\nthen exit nfs4_set_delegation without hashing the delegation, it will be\nfreed as soon as the callback is done with it, without ever being\nremoved from del_recall_lru.\n\nSymptoms show up later as use-after-free or list corruption warnings,\nusually in the laundromat thread.\n\nI suspect aba2072f4523 \"nfsd: grant read delegations to clients holding\nwrites\" made this bug easier to hit, but I looked as far back as v3.0\nand it looks to me it already had the same problem.  So I'm not sure\nwhere the bug was introduced; it may have been there from the beginning."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"04a8d07f3d58308b92630045560799a3faa3ebce","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"348714018139c39533c55661a0c7c990671396b4","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"33645d3e22720cac1e4548f8fef57bf0649536ee","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"2becaa990b93cbd2928292c0b669d3abb6cf06d4","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"e0759696de6851d7536efddfdd2dfed4c4df1f09","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"eeb0711801f5e19ef654371b627682aed3b11373","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"148c816f10fd11df27ca6a9b3238cdd42fa72cd3","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","status":"affected","lessThan":"548ec0805c399c65ed66c6641be467f717833ab5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4state.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"3.17","status":"affected"},{"version":"0","status":"unaffected","lessThan":"3.17","versionType":"semver"},{"version":"4.4.296","status":"unaffected","lessThanOrEqual":"4.4.*","versionType":"semver"},{"version":"4.9.294","status":"unaffected","lessThanOrEqual":"4.9.*","versionType":"semver"},{"version":"4.14.259","status":"unaffected","lessThanOrEqual":"4.14.*","versionType":"semver"},{"version":"4.19.222","status":"unaffected","lessThanOrEqual":"4.19.*","versionType":"semver"},{"version":"5.4.168","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.85","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.8","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"5.16","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4state.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/04a8d07f3d58308b92630045560799a3faa3ebce"},{"url":"https://git.kernel.org/stable/c/348714018139c39533c55661a0c7c990671396b4"},{"url":"https://git.kernel.org/stable/c/33645d3e22720cac1e4548f8fef57bf0649536ee"},{"url":"https://git.kernel.org/stable/c/2becaa990b93cbd2928292c0b669d3abb6cf06d4"},{"url":"https://git.kernel.org/stable/c/e0759696de6851d7536efddfdd2dfed4c4df1f09"},{"url":"https://git.kernel.org/stable/c/eeb0711801f5e19ef654371b627682aed3b11373"},{"url":"https://git.kernel.org/stable/c/148c816f10fd11df27ca6a9b3238cdd42fa72cd3"},{"url":"https://git.kernel.org/stable/c/548ec0805c399c65ed66c6641be467f717833ab5"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","baseScore":9.8,"baseSeverity":"CRITICAL"},"scenarios":[{"lang":"en","value":"AV:N - The vulnerable path is in the in-kernel NFS server (nfs4_set_delegation / nfsd4_cb_recall_prepare in fs/nfsd/nfs4state.c), reached when a remote NFSv4 client issues OPEN compounds over TCP/UDP 2049 that attempt to grant a read delegation.\nAC:L - A remote attacker controls both sides of the race by opening/requesting a delegation on one NFS client/session while concurrently issuing a conflicting open (e.g. write) from another client or session slot on separate nfsd threads, so success does not depend on conditions outside attacker influence.\nPR:N - Typical nfsd deployments use AUTH_SYS/AUTH_NULL with IP-based exports and no cryptographic authentication, so any host allowed by the export can EXCHANGE_ID/CREATE_SESSION/OPEN and exercise the delegation-grant path by self-asserting credentials.\nUI:N - The attacker alone drives the OPEN/delegation grant and the conflicting open that breaks the lease; 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