189 lines
14 KiB
JSON
189 lines
14 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-2026-64142",
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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": "2026-07-19T07:54:57.037Z",
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"datePublished": "2026-07-19T15:40:34.605Z",
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"dateUpdated": "2026-08-05T12:39:42.662Z"
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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": "2026-08-05T12:39:42.662Z"
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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\nksmbd: close durable scavenger races against m_fp_list lookups\n\nksmbd_durable_scavenger() has two related races against any walker\nthat iterates f_ci->m_fp_list, including ksmbd_lookup_fd_inode()\n(used by ksmbd_vfs_rename) and the share-mode checks in\nfs/smb/server/smb_common.c.\n\n(1) fp->node list-head reuse. Durable-preserved handles can remain\nlinked on f_ci->m_fp_list after session teardown so share-mode checks\nstill see them while the handle is reconnectable. The scavenger\ncollected expired handles by adding fp->node to a local\nscavenger_list after removing them from the global durable idr.\nBecause fp->node is the same list_head used by m_fp_list,\nlist_add(&fp->node, &scavenger_list) overwrites the m_fp_list links\nand corrupts both lists. CONFIG_DEBUG_LIST can report this on the\nshare-mode walk path.\n\n(2) Refcount race against m_fp_list walkers. The scavenger qualifies\nan expired durable handle with atomic_read(&fp->refcount) > 1 and\nfp->conn under global_ft.lock, removes fp from global_ft, then drops\nglobal_ft.lock before unlinking fp from m_fp_list and freeing it.\nDuring that gap fp is still linked on m_fp_list with f_state ==\nFP_INITED. ksmbd_lookup_fd_inode() under m_lock read calls\nksmbd_fp_get() (atomic_inc_not_zero on refcount that is still 1) and\ntakes a live reference; the scavenger then unlinks and frees fp\nwhile the holder owns a reference, leading to UAF on the holder's\nsubsequent ksmbd_fd_put() and on any field reads performed by a\nconcurrent share-mode walker that iterates m_fp_list without taking\nksmbd_fp_get() (smb_check_perm_dleases-like paths).\n\nFix both:\n\n * Stop reusing fp->node as a scavenger-private list node. Remove\n one expired handle from global_ft under global_ft.lock, take an\n explicit transient reference, drop the lock, unlink fp->node\n from m_fp_list under f_ci->m_lock, then drop both the durable\n lifetime and transient references with atomic_sub_and_test(2,\n &fp->refcount). If the scavenger is the last putter the close\n runs there; otherwise an in-flight holder that already raced\n through the m_fp_list lookup owns the final close via its\n ksmbd_fd_put() path. The one-at-a-time disposal can rescan the\n durable idr when multiple handles expire in the same pass, but\n durable scavenging is a background expiration path and the final\n full scan recomputes min_timeout before the next wait.\n\n * Clear fp->persistent_id inside __ksmbd_remove_durable_fd() right\n after idr_remove(), so a delayed final close from a holder that\n snatched fp does not re-issue idr_remove() on a persistent id\n that idr_alloc_cyclic() in ksmbd_open_durable_fd() may have\n already handed out to a brand-new durable handle.\n\n * Bypass the per-conn open_files_count decrement in\n __put_fd_final() when fp is detached from any session table\n (fp->conn cleared by session_fd_check() at durable preserve --\n paired with the volatile_id clear at unpublish, so checking\n fp->conn alone is sufficient). The walker that owns the final\n close runs from an unrelated work->conn whose\n stats.open_files_count never tracked this durable fp; without\n this guard the holder would underflow that unrelated counter.\n\nThe two races are folded into one patch because patch (1) alone\ncleans up the corrupted list but leaves a deterministic UAF window\nfor m_fp_list walkers that the transient-reference and\npersistent_id discipline in (2) close; bisecting onto an\nintermediate state would land on a UAF that pre-patch chaos merely\nmade less reproducible.\n\nValidation:\n * CONFIG_DEBUG_LIST coverage for the list_head reuse path.\n * KASAN-enabled direct SMB2 durable-handle coverage that exercised\n ksmbd_durable_scavenger() and non-NULL ksmbd_lookup_fd_inode()\n returns while durable handles expired under concurrent rename\n lookups, with no KASAN, UAF, list-corruption, ODEBUG, or WARNING\n reports.\n---truncated---"
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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:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 9.8,
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"baseSeverity": "CRITICAL"
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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:N - The bug is in ksmbd, the in-kernel SMB server reachable over TCP port 445; exploitation is driven by remote SMB2 packets that set up durable handles, tear down sessions, and issue concurrent rename/open operations.\nAC:L - The attacker controls both sides of the race by opening a durable handle, logging off/disconnecting to enter durable-preserve state, waiting for the configured scavenger timeout, and flooding concurrent SMB2 rename or create requests timed to the scavenger expiration window.\nPR:N - Exploitation requires only network reachability to ksmbd and normal SMB session authentication (including guest/anonymous shares); no pre-existing OS privileges, capabilities, or local access are needed beyond share-level SMB access obtainable through the protocol itself.\nUI:N - No victim user interaction is required beyond a server running ksmbd with durable handles enabled; the attacker drives the entire sequence of SMB operations programmatically.\nS:U - Impact is confined to kernel memory corruption and privilege escalation within the same kernel security boundary; this is not a VM escape or cross-authority boundary bypass.\nC:H - The refcount race produces a deterministic use-after-free on ksmbd_file structures, and share-mode walkers read fields from freed objects without refcount protection, enabling arbitrary kernel memory disclosure via heap reuse.\nI:H - Use-after-free on slab-allocated ksmbd_file objects and corruption of m_fp_list linked lists provide memory corruption primitives that can be leveraged for arbitrary kernel writes and control-flow hijacking.\nA:H - List corruption and use-after-free on kernel linked lists and file handle structures can cause kernel oops, BUG_ON from CONFIG_DEBUG_LIST, or panic, and the scavenger race is repeatable on each durable handle expiration cycle."
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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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"product": "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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"fs/smb/server/vfs_cache.c"
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"url": "https://git.kernel.org/stable/c/bf736184d063da1a552ffeff0481813599a182cc"
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"title": "ksmbd: close durable scavenger races against m_fp_list lookups",
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