{ "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": "2026-10-19T08:51:02.559Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:51:02.559Z" }, "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", "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" } ] } ] } ], "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" } } } }