{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89675", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.747Z", "datePublished": "2026-09-11T19:45:59.635Z", "dateUpdated": "2026-10-19T08:50:48.585Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:50:48.585Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: fix UAF in async copy cancel and shutdown\n\nAn async copy could be freed or used after free while a teardown caller\n(OFFLOAD_CANCEL, nfsd4_shutdown_copy, nfsd4_cancel_copy_by_sb) raced the\ncopy kthread:\n\n - find_async_copy() bumped copy->refcount but left the copy on\n clp->async_copies, so the reaper's cleanup_async_copy() could run\n release_copy_files() concurrently with a cancel/shutdown caller. Both\n put and NULL nf_src/nf_dst without a common lock, double-putting the\n nfsd_file and freeing it early.\n\n - nfsd4_do_async_copy() set NFSD4_COPY_F_STOPPED before its final uses\n of the copy (nfsd_update_cmtime_attr() on copy->nf_dst,\n nfsd4_send_cb_offload()). nfsd4_stop_copy() treats a set STOPPED bit\n as \"kthread done, skip kthread_stop()\", so a teardown caller ran\n release_copy_files() -- which puts and NULLs nf_dst -- while the\n kthread still dereferenced it (NULL/UAF).\n\n - copy->copy_task was never pinned. The one-shot kthread self-reaps on\n return, so kthread_stop()'s get_task_struct() could touch a freed\n task_struct.\n\n - co_cb is embedded in the copy, but nfsd4_send_cb_offload() held a\n reference only on the client, so a concurrent teardown could free\n the copy while the CB_OFFLOAD callback was in flight.\n\nFix the teardown lifetime as a whole:\n\n - find_async_copy() unlinks the copy (clear cp_clp, list_del_init)\n under async_lock; the cancel, shutdown, and sb-cancel paths drop the\n list-membership reference via nfs4_put_copy() after nfsd4_stop_copy().\n Drop the now-redundant list_del fixup from cleanup_async_copy().\n\n - Because unlinking hides the copy from the reaper, its\n cleanup_async_copy() can no longer remove the copy's s2s_cp_stateids\n entry; the cancel/shutdown/sb-cancel paths now call\n nfs4_free_copy_state() themselves (while cp_clp is still valid) so\n the entry does not dangle at freed memory for the laundromat and\n manage_cpntf_state() to dereference.\n\n - Give the kthread its own reference, taken in nfsd4_copy() before\n wake_up_process() and dropped at the end of nfsd4_do_async_copy();\n call wake_up_process() before list_add().\n\n - Pin the task_struct with get_task_struct() in nfsd4_copy(), released\n in nfs4_put_copy(), so kthread_stop() is safe whenever the kthread\n exits. Set NFSD4_COPY_F_STOPPED only in nfsd4_stop_copy(), which now\n always kthread_stop()s before release_copy_files(); completion is\n still reported via NFSD4_COPY_F_COMPLETED, so\n nfsd4_has_active_async_copies() is unaffected. Each teardown caller\n removes the copy from clp->async_copies first, so kthread_stop() runs\n exactly once.\n\n - Take a copy reference in nfsd4_send_cb_offload(), dropped in\n nfsd4_cb_offload_release(). The kthread still holds its own reference\n there, so the refcount_inc() cannot race the final free.\n\n - Read cp_clp with smp_load_acquire() to pair with the unordered\n set_bit()/clear_bit() writers (Documentation/atomic_bitops.rst)." } ], "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 flaw is in nfsd's NFSv4.2 OP_COPY and OP_OFFLOAD_CANCEL handlers (nfsd4_copy/nfsd4_offload_cancel in fs/nfsd/nfs4proc.c), reached by sending COMPOUND RPCs over TCP port 2049 to the in-kernel NFS server; no local access to the host is required.\nAC:L - The attacker controls both sides of the race by starting an async COPY then issuing OFFLOAD_CANCEL or DESTROY_CLIENTID, and can stall CB_OFFLOAD replies so the embedded callback stays in flight on freed memory; the window is retryable and does not depend on uninfluenced victim state.\nPR:N - Under AUTH_SYS, the default NFS configuration, the server verifies no secret; EXCHANGE_ID, CREATE_SESSION, and OPEN succeed for any host permitted by the export, so a remote NFSv4.2 client needs no kernel-verified credentials or local privileges on the server.\nUI:N - The attacker's own NFS client issues COPY and OFFLOAD_CANCEL (or DESTROY_CLIENTID) against an already-running nfsd export; no administrator or other user action on the server is required.\nS:U - Impact is kernel heap use-after-free and nfsd state corruption within the same host kernel security authority; it does not cross a VM, hypervisor, or IOMMU boundary.\nC:H - Use-after-free of the nfsd4_copy object (including its embedded nfsd4_callback), nfsd_file src/dst objects, and the copy kthread task_struct allows slab reuse that can be leveraged for arbitrary kernel memory reads.\nI:H - The same UAFs enable heap spraying and arbitrary writes; CB_OFFLOAD work and rpc_task callbacks invoke cb_ops function pointers that live inside the freed copy, supporting control-flow hijack.\nA:H - Concurrent release_copy_files() double-puts nfsd_file, kthread_stop() can touch a self-reaped task_struct, and the copy kthread can NULL-dereference nf_dst after teardown, each of which oopses or panics the kernel." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/nfsd/nfs4proc.c" ], "versions": [ { "version": "e0639dc5805a9d4faaa2c07ad98fa853b9529dd3", "lessThan": "9031493ef7369d5c59c4bacc96f0c85965f09a98", "status": "affected", "versionType": "git" }, { "version": "e0639dc5805a9d4faaa2c07ad98fa853b9529dd3", "lessThan": "a385cf5e016b748babf94cc664e43a26e17db117", "status": "affected", "versionType": "git" }, { "version": "e0639dc5805a9d4faaa2c07ad98fa853b9529dd3", "lessThan": "62c0f6eaf050bb9284c1f9cac6ed1770092e6b95", "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/nfs4proc.c" ], "versions": [ { "version": "4.20", "status": "affected" }, { "version": "0", "lessThan": "4.20", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.51", "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": "4.20", "versionEndExcluding": "6.18.51" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.20", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "4.20", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/9031493ef7369d5c59c4bacc96f0c85965f09a98" }, { "url": "https://git.kernel.org/stable/c/a385cf5e016b748babf94cc664e43a26e17db117" }, { "url": "https://git.kernel.org/stable/c/62c0f6eaf050bb9284c1f9cac6ed1770092e6b95" } ], "title": "nfsd: fix UAF in async copy cancel and shutdown", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2026-89675", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "total" } ], "version": "2.0.3", "timestamp": "2026-10-16T19:25:50.674765Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-16T19:26:48.362Z" } } ] } }