{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2021-47506","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2024-05-22T06:20:56.205Z","datePublished":"2024-05-24T15:01:52.746Z","dateUpdated":"2026-08-05T08:48:10.240Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-08-05T08:48:10.240Z"},"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."}],"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; no victim user or administrator action on the server is required.\nS:U - The use-after-free corrupts kernel slab memory (nfs4_delegation on del_recall_lru) within the host nfsd security authority and does not cross a VM, IOMMU, or other separate boundary.\nC:H - The unhashed delegation is freed while still linked on del_recall_lru; later laundromat traversal is a classic slab UAF that can be groomed/reallocated to disclose arbitrary kernel memory.\nI:H - The same freed nfs4_delegation object remains on del_recall_lru so laundromat list operations write into attacker-reclaimable heap, yielding an arbitrary-write / control-flow hijack primitive.\nA:H - Use-after-free and list corruption of del_recall_lru reliably cause kernel oops/panic in the laundromat thread, fully disrupting availability of the NFS server host."}]}],"affected":[{"product":"Linux","vendor":"Linux","defaultStatus":"unaffected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4state.c"],"versions":[{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"04a8d07f3d58308b92630045560799a3faa3ebce","status":"affected","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"348714018139c39533c55661a0c7c990671396b4","status":"affected","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"33645d3e22720cac1e4548f8fef57bf0649536ee","status":"affected","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"2becaa990b93cbd2928292c0b669d3abb6cf06d4","status":"affected","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"e0759696de6851d7536efddfdd2dfed4c4df1f09","status":"affected","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"eeb0711801f5e19ef654371b627682aed3b11373","status":"affected","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"148c816f10fd11df27ca6a9b3238cdd42fa72cd3","status":"affected","versionType":"git"},{"version":"dff1399f8addf7129c49bb2227469da79cc30b47","lessThan":"548ec0805c399c65ed66c6641be467f717833ab5","status":"affected","versionType":"git"}]},{"product":"Linux","vendor":"Linux","defaultStatus":"affected","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/nfsd/nfs4state.c"],"versions":[{"version":"3.17","status":"affected"},{"version":"0","lessThan":"3.17","status":"unaffected","versionType":"semver"},{"version":"4.4.296","lessThanOrEqual":"4.4.*","status":"unaffected","versionType":"semver"},{"version":"4.9.294","lessThanOrEqual":"4.9.*","status":"unaffected","versionType":"semver"},{"version":"4.14.259","lessThanOrEqual":"4.14.*","status":"unaffected","versionType":"semver"},{"version":"4.19.222","lessThanOrEqual":"4.19.*","status":"unaffected","versionType":"semver"},{"version":"5.4.168","lessThanOrEqual":"5.4.*","status":"unaffected","versionType":"semver"},{"version":"5.10.85","lessThanOrEqual":"5.10.*","status":"unaffected","versionType":"semver"},{"version":"5.15.8","lessThanOrEqual":"5.15.*","status":"unaffected","versionType":"semver"},{"version":"5.16","lessThanOrEqual":"*","status":"unaffected","versionType":"original_commit_for_fix"}]}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"4.4.296"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"4.9.294"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"4.14.259"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"4.19.222"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"5.4.168"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"5.10.85"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"5.15.8"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"3.17","versionEndExcluding":"5.16"}]}]}],"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"}],"title":"nfsd: 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