{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89631", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.738Z", "datePublished": "2026-09-11T19:45:26.444Z", "dateUpdated": "2026-10-21T12:48:03.355Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-21T12:48:03.355Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: reject a tree connect response whose byte count is too small\n\nCIFSTCon() bounds its strnlen() over the byte area with the server's\nByteCount minus two, which for ByteCount 0 or 1 goes negative as an int\nand converts to a huge size_t. The later subtraction wraps the __u16\nbytes_left, and that is what bounds cifs_strndup_from_utf16(): a bound of\nup to 65535 against a ~16 KB cifs_req_poolp object runs off the end of the\nslab object, and the bytes reach userspace through tcon->nativeFileSystem\nin /proc/fs/cifs/DebugData.\n\nReject a byte area too small for what the parser consumes. Two bytes is\nthe least it can consume, and no conformant response carries fewer. The\nnew trace point is the 129th smb_eio_trace entry, which __mode(byte)\ncannot represent, so the attribute goes with it." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H", "baseScore": 9.1, "baseSeverity": "CRITICAL" }, "scenarios": [ { "lang": "en", "value": "AV:N - CIFSTCon() parses a TREE_CONNECT_ANDX response received over TCP (typically port 445) from the SMB peer, so a malicious or compromised CIFS server supplies the undersized ByteCount remotely.\nAC:L - A server that returns success with ByteCount 0 or 1 triggers the integer underflow and wrapped 65535-byte bound deterministically; CONFIG_CIFS_ALLOW_INSECURE_LEGACY defaults to y, and no race or uncontrolled memory layout is required.\nPR:N - The attacker is the remote SMB server (or a MITM on unsigned SMB1); the client authenticates to that peer, so no account, capability, or privilege on the victim host is required.\nUI:N - Existing SMB1 mounts, IPC tcons, automounts, fstab, and cifsroot reconnect via cifs_tree_connect() after a server-induced TCP drop, so the crafted TREE_CONNECT response is processed without contemporaneous user action.\nS:U - The out-of-bounds slab read, kernel-memory leak, and possible oops remain inside the client kernel's security authority and do not cross a VM, IOMMU, or sandbox boundary.\nC:H - ByteCount underflow wraps the __u16 bound to up to 65535 bytes against a ~16KB cifs_request slab, so cifs_strndup_from_utf16() copies adjacent kernel heap into tcon->nativeFileSystem, which is then exposed through /proc/fs/cifs/DebugData.\nI:N - The defect is an out-of-bounds read copied into a newly allocated, correctly sized string; it does not write outside that allocation or provide an arbitrary-write or control-flow primitive.\nA:H - strnlen(), kstrndup(), and cifs_utf16_bytes() walk tens of kilobytes past the cifs_request object into unmapped or guarded pages, causing a kernel oops or panic that a malicious peer can retrigger on reconnect." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/smb/client/cifssmb.c", "fs/smb/client/trace.h" ], "versions": [ { "version": "cc20c031bb067eb3280a1c4b5c42295093e24863", "lessThan": "d837645a719151ed392d4d9cab4571c2753dab12", "status": "affected", "versionType": "git" }, { "version": "cc20c031bb067eb3280a1c4b5c42295093e24863", "lessThan": "2ae219762ebac929bf6ab3473681f10ed566af08", "status": "affected", "versionType": "git" }, { "version": "cc20c031bb067eb3280a1c4b5c42295093e24863", "lessThan": "3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d", "status": "affected", "versionType": "git" }, { "version": "cc20c031bb067eb3280a1c4b5c42295093e24863", "lessThan": "411e484fe71a7f1028de617447edad9cb6d9d68a", "status": "affected", "versionType": "git" }, { "version": "cc20c031bb067eb3280a1c4b5c42295093e24863", "lessThan": "65deb18359341141d37dc86fc7853511be3c87a7", "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/smb/client/cifssmb.c", "fs/smb/client/trace.h" ], "versions": [ { "version": "2.6.30", "status": "affected" }, { "version": "0", "lessThan": "2.6.30", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.160", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.114", "lessThanOrEqual": "6.12.*", "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": "2.6.30", "versionEndExcluding": "6.6.160" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.30", "versionEndExcluding": "6.12.114" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.30", "versionEndExcluding": "6.18.51" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.30", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.30", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/d837645a719151ed392d4d9cab4571c2753dab12" }, { "url": "https://git.kernel.org/stable/c/2ae219762ebac929bf6ab3473681f10ed566af08" }, { "url": "https://git.kernel.org/stable/c/3be89e8039a85fa3b6cd5f9dcc4c1459eb356c2d" }, { "url": "https://git.kernel.org/stable/c/411e484fe71a7f1028de617447edad9cb6d9d68a" }, { "url": "https://git.kernel.org/stable/c/65deb18359341141d37dc86fc7853511be3c87a7" } ], "title": "smb: client: reject a tree connect response whose byte count is too small", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2026-89631", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "version": "2.0.3", "timestamp": "2026-10-16T19:24:39.378892Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-16T19:26:45.378Z" } } ] } }