{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89689","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","state":"PUBLISHED","assignerShortName":"Linux","dateReserved":"2026-09-11T19:38:34.749Z","datePublished":"2026-09-11T19:46:09.976Z","dateUpdated":"2026-09-13T06:33:13.546Z"},"containers":{"cna":{"providerMetadata":{"orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux","dateUpdated":"2026-09-13T06:33:13.546Z"},"descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: don't free session slots that are still in use\n\nnfsd4_sequence() can free the very slot it is currently processing.\nWhen the session shrinker has reduced se_target_maxslots below\nse_fchannel.maxreqs, the shrink path checks three conditions before\ncalling free_session_slots():\n\n  1. se_target_maxslots < maxreqs  (shrink was advertised)\n  2. slot->sl_generation == se_slot_gen  (slot is up-to-date)\n  3. seq->maxslots <= se_target_maxslots  (client acknowledges)\n\nHowever, seq->slotid is never checked against se_target_maxslots.\nA client using a slot in the range [se_target_maxslots, maxreqs) can\nsatisfy all three conditions: its slot has the current generation\n(set by a prior SEQUENCE), and it sends sa_highest_slotid <=\nse_target_maxslots to acknowledge the reduction.\n\nfree_session_slots() then kfrees every slot at index >=\nse_target_maxslots, including the caller's own slot. The function\ncontinues to write sl_seqid, sl_flags, sl_generation, and stores the\ndangling pointer in cstate->slot. Later, nfsd4_store_cache_entry()\ncopies up to maxresp_cached bytes of the compound reply into the freed\nsl_data[] array, corrupting whatever slab object now occupies that\naddress.\n\nAdditionally, a concurrent thread processing SEQUENCE on a different\nhigh-numbered slot can have its slot freed out from under it.\nNFSD4_SLOT_INUSE is set under nn->client_lock before the lock is\nreleased, so any concurrent thread past SEQUENCE will have its slot\nmarked. However, free_session_slots() does not check NFSD4_SLOT_INUSE\nbefore freeing.\n\nFix both problems by:\n 1. Checking that the current request's slotid is below the shrink\n    boundary.\n 2. Scanning slots in the to-be-freed range for NFSD4_SLOT_INUSE and\n    deferring the shrink if any are active."}],"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 bug is in nfsd4_sequence() in the in-kernel NFSv4.1 server (fs/nfsd/nfs4state.c). A remote client reaches it by sending COMPOUND RPCs with OP_SEQUENCE over TCP/2049 after EXCHANGE_ID/CREATE_SESSION; no local access to the NFS server is required.\nAC:L - After CREATE_SESSION with multiple slots, the attacker can grow the slot table and consume DRC memory so the nfsd-DRC-slot shrinker lowers se_target_maxslots, which SEQUENCE replies report. A SEQUENCE on a high slotid with sa_highest_slotid acknowledging the shrink then kfree's that in-use slot. Slotid, maxslots, cachethis, and concurrent COMPOUNDs are attacker-controlled.\nPR:N - Typical nfsd deployments accept AUTH_SYS/AUTH_NULL without cryptographic authentication. Any host allowed by the export ACL can EXCHANGE_ID/CREATE_SESSION and then SEQUENCE (ALLOWED_WITHOUT_FH, no filehandle or OPEN required); no local account or capability on the NFS server is needed.\nUI:N - The attacking NFS client sends the EXCHANGE_ID, CREATE_SESSION, and crafted SEQUENCE compounds itself. No victim user or administrator action on the NFS server, such as mounting an export or opening a file, is required.\nS:U - The use-after-free corrupts nfsd session-slot heap objects inside the NFS server host kernel. Impact stays in that kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - free_session_slots() kfree's the nfsd4_slot still referenced by cstate->slot. Later nfsd4_store_cache_entry() and SEQUENCE processing read the freed object, including sl_cred. Slab reuse of the DRC slot (up to 2048-byte sl_data) enables arbitrary kernel memory disclosure per UAF guidance.\nI:H - After the kfree, nfsd4_sequence() writes sl_seqid, sl_flags, and sl_generation through the dangling pointer, and nfsd4_store_cache_entry() copies up to maxresp_cached bytes of the compound reply into freed sl_data[] and runs free_svc_cred() on reused memory, yielding a kernel heap write/arbitrary-free primitive.\nA:H - Use-after-free of the in-use session slot oopses or panics nfsd when the dangling cstate->slot is dereferenced or when concurrent SEQUENCE threads hit a freed slot. The attacker can repeat the SEQUENCE compounds to deny NFS service and take down the 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":"fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7","lessThan":"72d40b103bb03f0124d3a3c8f71a30cbafaf6afa","status":"affected","versionType":"git"},{"version":"fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7","lessThan":"b449b134e7762ddf98653a4b1d3e76d2d212ea64","status":"affected","versionType":"git"},{"version":"fc8738c68d0bbf5033dd98b4f63d277ecbd49fd7","lessThan":"f5d22e372f4ac3eb287037a488c29691d52a6330","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":"6.14","status":"affected"},{"version":"0","lessThan":"6.14","status":"unaffected","versionType":"semver"},{"version":"6.18.50","lessThanOrEqual":"6.18.*","status":"unaffected","versionType":"semver"},{"version":"7.2.4","lessThanOrEqual":"7.2.*","status":"unaffected","versionType":"semver"},{"version":"7.3-rc1","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":"6.14","versionEndExcluding":"6.18.50"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.14","versionEndExcluding":"7.3-rc1"}]}]}],"references":[{"url":"https://git.kernel.org/stable/c/72d40b103bb03f0124d3a3c8f71a30cbafaf6afa"},{"url":"https://git.kernel.org/stable/c/b449b134e7762ddf98653a4b1d3e76d2d212ea64"},{"url":"https://git.kernel.org/stable/c/f5d22e372f4ac3eb287037a488c29691d52a6330"}],"title":"nfsd: don't free session slots that are still in use","x_generator":{"engine":"bippy-1.2.0"}}}}