175 lines
11 KiB
JSON
175 lines
11 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-89670",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2026-09-11T19:38:34.746Z",
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"datePublished": "2026-09-11T19:45:55.846Z",
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"dateUpdated": "2026-10-19T08:50:43.628Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-10-19T08:50:43.628Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: hold rcu across localio cmpxchg retry\n\nnfsd_file objects are freed via call_rcu (filecache.c:296), and\nnfsd_file_slab is created without SLAB_TYPESAFE_BY_RCU\n(KMEM_CACHE(nfsd_file, 0) at filecache.c:789), so the slab page\nbacking a freed nfsd_file becomes freely reclaimable once the RCU\ngrace period elapses.\n\nThe again: retry block in nfsd_open_local_fh() loads a pointer with\ncmpxchg and then calls nfsd_file_get(new) (which is\nrefcount_inc_not_zero) without holding rcu_read_lock. The sole caller\nnfs_open_local_fh() drops rcu_read_lock before invoking this helper,\nso no outer reader-side critical section covers the load.\n\n CPU 0 (nfsd_open_local_fh) CPU 1 (nfsd_file_put_local)\n ----- -----\n new = cmpxchg(pnf, NULL, ...)\n nf = xchg(pnf, NULL)\n nfsd_file_put(nf)\n last ref -> call_rcu()\n /* grace period elapses;\n slab page recycled */\n nfsd_file_get(new)\n refcount_inc_not_zero(&new->nf_ref)\n /* operates on recycled memory */\n\nA non-zero word at the nf_ref offset of the recycled object makes the\nrefcount bump appear to succeed, and the caller then dereferences\nnew->nf_net and new->nf_file out of freed memory.\n\nFix by taking rcu_read_lock() immediately before the cmpxchg and\nreleasing it on all three exits of the if (new) block: the goto-again\nretry, the lost-race cleanup path, and the install-succeeded path.\nnfsd_file_put() and nfsd_net_put() stay outside the RCU section so\nthey remain free to block."
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - nfsd_open_local_fh is invoked only from the NFS client's LOCALIO path (nfs_generic_pg_pgios/nfs_commit_list → nfs_local_open_fh) after a same-host UUID handshake; a remote NFS peer never reaches this cmpxchg retry, so exploitation requires local access to a loopback NFS mount.\nAC:L - The attacker controls both sides of the race: concurrent read/write/commit syscalls enter nfsd_open_local_fh while close/put_nfs_open_context runs nfsd_file_put_local on the same nfs_file_localio slot; the sequence is repeatable at will and can be widened by preemption.\nPR:L - Any unprivileged local user who can open files on a LOCALIO-enabled NFS mount can reach nfs_generic_pg_pgios → nfsd_open_local_fh with no capability check; starting nfsd or creating the mount is a deployment precondition, not a privilege the attacker must hold.\nUI:N - The attacker triggers the use-after-free from their own threads via I/O and close syscalls; no separate victim action is required once the LOCALIO mount exists.\nS:U - The use-after-free corrupts nfsd_file slab objects in the host kernel, which is standard kernel memory corruption within one security authority, not a VM escape, IOMMU bypass, or sandbox boundary crossing.\nC:H - nfsd_file is freed via call_rcu without SLAB_TYPESAFE_BY_RCU, so after the grace period nfsd_file_get and later nf_file/nf_net dereferences operate on recycled memory, enabling an arbitrary kernel read or disclosure of another exported file's contents.\nI:H - refcount_inc_not_zero writes into the recycled nfsd_file, and the stale pointer is then used for write_iter, corrupting another object's refcount and enabling a follow-on premature free and control-flow hijack.\nA:H - Use-after-free on the nfsd_file slab causes slab corruption, refcount warnings, and oops/panic when nf_file is taken from freed memory, which is a repeatable local kernel denial of service."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"fs/nfsd/localio.c"
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],
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"versions": [
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{
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"version": "e6f7e1487ab528a6c653bd0d42812ff2942846cd",
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"lessThan": "763c0bad872368304db718f79af7e93048885c67",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "e6f7e1487ab528a6c653bd0d42812ff2942846cd",
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"lessThan": "559570f91a7d4d199a72105e4980bef791f4cbf1",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "e6f7e1487ab528a6c653bd0d42812ff2942846cd",
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"lessThan": "58884694978a3d7d111edb433d7fd6a6c5af2f34",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "986a21ace186433e0397a59491646edad8c8d636",
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"status": "affected",
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"versionType": "git"
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},
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{
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"version": "6.15.3",
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"lessThan": "6.16",
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"status": "affected",
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"versionType": "semver"
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}
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]
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},
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "affected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"fs/nfsd/localio.c"
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],
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"versions": [
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{
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"version": "6.16",
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"status": "affected"
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},
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{
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"version": "0",
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"lessThan": "6.16",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "6.18.50",
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"lessThanOrEqual": "6.18.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.2.4",
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"lessThanOrEqual": "7.2.*",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.3",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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],
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"cpeApplicability": [
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{
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"nodes": [
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{
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"operator": "OR",
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"negate": false,
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"cpeMatch": [
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.16",
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"versionEndExcluding": "6.18.50"
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},
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.16",
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"versionEndExcluding": "7.2.4"
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},
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.16",
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"versionEndExcluding": "7.3"
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},
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.15.3"
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}
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]
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}
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]
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}
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],
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"references": [
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{
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"url": "https://git.kernel.org/stable/c/763c0bad872368304db718f79af7e93048885c67"
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},
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{
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"url": "https://git.kernel.org/stable/c/559570f91a7d4d199a72105e4980bef791f4cbf1"
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},
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{
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"url": "https://git.kernel.org/stable/c/58884694978a3d7d111edb433d7fd6a6c5af2f34"
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}
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],
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"title": "nfsd: hold rcu across localio cmpxchg retry",
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"x_generator": {
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"engine": "bippy-1.2.0"
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}
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} |