{"id":"CVE-2026-31718","state":"PUBLISHED","title":"ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger\n\nWhen a durable file handle survives session disconnect (TCP close without\nSMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the\nhandle for later reconnection. However, it did not clean up the byte-range\nlocks on fp->lock_list.\n\nLater, when the durable scavenger thread times out and calls\n__ksmbd_close_fd(NULL, fp), the lock cleanup loop did:\n\n    spin_lock(&fp->conn->llist_lock);\n\nThis caused a slab use-after-free because fp->conn was NULL and the\noriginal connection object had already been freed by\nksmbd_tcp_disconnect().\n\nThe root cause is asymmetric cleanup: lock entries (smb_lock->clist) were\nleft dangling on the freed conn->lock_list while fp->conn was nulled out.\n\nTo fix this issue properly, we need to handle the lifetime of\nsmb_lock->clist across three paths:\n - Safely skip clist deletion when list is empty and fp->conn is NULL.\n - Remove the lock from the old connection's lock_list in\n   session_fd_check()\n - Re-add the lock to the new connection's lock_list in\n   ksmbd_reopen_durable_fd().","publishedAt":"2026-05-01T13:56:12.680Z","updatedAt":"2026-08-05T12:24:49.667Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"8df4bcdb0a4232192b2445256c39b787d58ef14d","status":"affected","lessThan":"0000a7780e0e446a28a273572f6ea8f7f582f694","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"e33c65f011980b4ad4abfd93585ec2079856368f","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"3d6682726c2d3a46d31dae88b8166786b09b03ad","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"235e32320a470fcd3998fb3774f2290a0eb302a1","versionType":"git"},{"version":"6.6.32","status":"affected","lessThan":"6.6.140","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/vfs_cache.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.9","versionType":"semver"},{"version":"6.6.140","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.84","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.25","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.2","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/vfs_cache.c"]}],"references":["https://git.kernel.org/stable/c/0000a7780e0e446a28a273572f6ea8f7f582f694","https://git.kernel.org/stable/c/e33c65f011980b4ad4abfd93585ec2079856368f","https://git.kernel.org/stable/c/3d6682726c2d3a46d31dae88b8166786b09b03ad","https://git.kernel.org/stable/c/b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9","https://git.kernel.org/stable/c/235e32320a470fcd3998fb3774f2290a0eb302a1"],"weaknesses":[],"ingestedAt":"2026-10-29T20:11:40.391Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/31xxx/CVE-2026-31718.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-31718","state":"PUBLISHED","datePublished":"2026-05-01T13:56:12.680Z","dateUpdated":"2026-08-05T12:24:49.667Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-03-09T15:48:24.134Z"},"containers":{"cna":{"title":"ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger\n\nWhen a durable file handle survives session disconnect (TCP close without\nSMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the\nhandle for later reconnection. However, it did not clean up the byte-range\nlocks on fp->lock_list.\n\nLater, when the durable scavenger thread times out and calls\n__ksmbd_close_fd(NULL, fp), the lock cleanup loop did:\n\n    spin_lock(&fp->conn->llist_lock);\n\nThis caused a slab use-after-free because fp->conn was NULL and the\noriginal connection object had already been freed by\nksmbd_tcp_disconnect().\n\nThe root cause is asymmetric cleanup: lock entries (smb_lock->clist) were\nleft dangling on the freed conn->lock_list while fp->conn was nulled out.\n\nTo fix this issue properly, we need to handle the lifetime of\nsmb_lock->clist across three paths:\n - Safely skip clist deletion when list is empty and fp->conn is NULL.\n - Remove the lock from the old connection's lock_list in\n   session_fd_check()\n - Re-add the lock to the new connection's lock_list in\n   ksmbd_reopen_durable_fd()."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"8df4bcdb0a4232192b2445256c39b787d58ef14d","status":"affected","lessThan":"0000a7780e0e446a28a273572f6ea8f7f582f694","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"e33c65f011980b4ad4abfd93585ec2079856368f","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"3d6682726c2d3a46d31dae88b8166786b09b03ad","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9","versionType":"git"},{"version":"c8efcc786146a951091588e5fa7e3c754850cb3c","status":"affected","lessThan":"235e32320a470fcd3998fb3774f2290a0eb302a1","versionType":"git"},{"version":"6.6.32","status":"affected","lessThan":"6.6.140","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/vfs_cache.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.9","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.9","versionType":"semver"},{"version":"6.6.140","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.84","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.25","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.2","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/vfs_cache.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/0000a7780e0e446a28a273572f6ea8f7f582f694"},{"url":"https://git.kernel.org/stable/c/e33c65f011980b4ad4abfd93585ec2079856368f"},{"url":"https://git.kernel.org/stable/c/3d6682726c2d3a46d31dae88b8166786b09b03ad"},{"url":"https://git.kernel.org/stable/c/b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9"},{"url":"https://git.kernel.org/stable/c/235e32320a470fcd3998fb3774f2290a0eb302a1"}],"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 - ksmbd is an in-kernel SMB server reachable over TCP/IP, and the vulnerable durable-handle and byte-range-lock paths are driven by SMB2 network requests.\nAC:L - The attacker can create the durable handle, add a lock, disconnect TCP without SMB2_LOGOFF, and wait for the durable scavenger; no race or condition outside attacker control is required.\nPR:N - The path requires an SMB session and tree connection, but ksmbd supports guest/anonymous sessions and guest shares, making a no-credential network attack a reasonable high-severity deployment scenario.\nUI:N - No victim interaction is required once the ksmbd service is exposed; the attacker sends SMB2 requests and closes the connection.\nS:U - The bug corrupts kernel/ksmbd state within the same security authority and does not cross a VM, IOMMU, or sandbox boundary.\nC:H - This is a kernel use-after-free involving dangling list entries tied to freed connection state, and such memory corruption can plausibly be shaped into kernel memory disclosure.\nI:H - The same UAF/list corruption can plausibly be leveraged for kernel memory corruption or control-flow impact, so high integrity impact is warranted.\nA:H - At minimum, triggering the scavenger cleanup can dereference freed or invalid connection/list state and crash the kernel."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:24:49.667Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.6.32","versionEndExcluding":"6.6.140"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.9","versionEndExcluding":"6.12.84"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.9","versionEndExcluding":"6.18.25"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.9","versionEndExcluding":"7.0.2"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.9","versionEndExcluding":"7.1"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}