CVE-2026-64400

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When a crafted path attempts to\nescape the share boundary using parent-directory components ('..'),\nvfs_path_parent_lookup() detects this and immediately fails,\nreturning -EXDEV.\n\nHowever, a bug exists in __ksmbd_vfs_kern_path() under caseless mode.\nThe function fails to intercept the -EXDEV error and erroneously\nfalls through to the caseless retry logic, which is intended only\nfor genuinely missing files. During this retry process, the path\nis reconstructed, leading to an unintended LOOKUP_BENEATH bypass\nthat allows write-capable users to create zero-length files or\ndirectories outside the exported share.\n\nFix this by ensuring that the execution only proceeds to the caseless\nlookup retry when the error is specifically -ENOENT. Any other errors,\nsuch as -EXDEV from a path traversal attempt, must be returned immediately."}], "metrics": [{"cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H", "baseScore": 8.6, "baseSeverity": "HIGH"}, "scenarios": [{"lang": "en", "value": "AV:N - The vulnerable lookup is reached remotely through SMB2 CREATE requests handled by ksmbd over TCP/445.\nAC:L - The attacker controls the crafted parent-directory path and can issue repeated or concurrent requests; any required lookup/create race is attacker-driven.\nPR:N - Although a valid SMB session and writable tree connection are required, ksmbd supports anonymous guest sessions on writable shares, requiring no prior privileges in a reasonable deployment.\nUI:N - Exploitation requires only attacker-generated SMB requests and no action by a victim.\nS:U - The bypass affects filesystems managed by the same host kernel and does not cross a virtualization or comparable security authority boundary.\nC:L - File contents are not exposed, but the out-of-share caseless directory walk and distinguishable errors can disclose limited pathname-existence metadata.\nI:L - The attacker can create chosen zero-length files or directories outside the export, but cannot supply file contents or overwrite arbitrary existing data through this flaw.\nA:H - Repeated creation in an escaped world-writable location can exhaust root-filesystem inodes, storage, or tmpfs memory and cause system-wide service unavailability."}]}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/server/vfs.c"], "versions": [{"version": "6927ffe7479c72e7ebf885507227266a75f7c97d", "lessThan": "21f050439db157f2afcc19885dec14549ca6ffc0", "status": "affected", "versionType": "git"}, {"version": "74d7970febf7e9005375aeda0df821d2edffc9f7", "lessThan": "eec1dd2586c4016b7555a5d047db2b3756459fb2", "status": "affected", "versionType": "git"}, {"version": "74d7970febf7e9005375aeda0df821d2edffc9f7", "lessThan": "a1c331d98313380c38f616c8b28b890ec8ef9c28", "status": "affected", "versionType": "git"}, {"version": "74d7970febf7e9005375aeda0df821d2edffc9f7", "lessThan": "cfb5a56c218888f9d74165dff0c282cd0be97983", "status": "affected", "versionType": "git"}, {"version": "74d7970febf7e9005375aeda0df821d2edffc9f7", "lessThan": "8c9a4f1327eb71efbf14842e7b8a6d965077eb67", "status": "affected", "versionType": "git"}, {"version": "74d7970febf7e9005375aeda0df821d2edffc9f7", "lessThan": "54bab9ba5a9f156ffa9324fcbe5a356fd0242f95", "status": "affected", "versionType": "git"}, {"version": "019aae488dbc67c97a33db03652e20e2c9e3afa7", "status": "affected", "versionType": "git"}, {"version": "ef6cc1c465786b3e4e735d1ab8b616b3e94402df", "status": "affected", "versionType": "git"}, {"version": "6.1.71", "lessThan": "6.1.191", "status": "affected", "versionType": "semver"}, {"version": "5.15.145", "lessThan": "5.16", "status": "affected", "versionType": "semver"}, {"version": "6.3.10", "lessThan": "6.4", "status": "affected", "versionType": "semver"}]}, {"product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["fs/smb/server/vfs.c"], "versions": [{"version": "6.4", "status": "affected"}, {"version": "0", "lessThan": "6.4", "status": "unaffected", "versionType": "semver"}, {"version": "6.1.191", "lessThanOrEqual": "6.1.*", "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": "6.18.57", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.1.4", "lessThanOrEqual": "7.1.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.2", "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": "6.1.71", "versionEndExcluding": "6.1.191"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.6.160"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.12.114"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "6.18.57"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "7.1.4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.4", "versionEndExcluding": "7.2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "5.15.145"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.3.10"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/21f050439db157f2afcc19885dec14549ca6ffc0"}, {"url": "https://git.kernel.org/stable/c/eec1dd2586c4016b7555a5d047db2b3756459fb2"}, {"url": "https://git.kernel.org/stable/c/a1c331d98313380c38f616c8b28b890ec8ef9c28"}, {"url": "https://git.kernel.org/stable/c/cfb5a56c218888f9d74165dff0c282cd0be97983"}, {"url": "https://git.kernel.org/stable/c/8c9a4f1327eb71efbf14842e7b8a6d965077eb67"}, {"url": "https://git.kernel.org/stable/c/54bab9ba5a9f156ffa9324fcbe5a356fd0242f95"}], "title": "ksmbd: prevent path traversal bypass by restricting caseless retry", "x_generator": {"engine": "bippy-1.2.0"}}}}

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When a crafted path attempts to\nescape the share boundary using parent-directory components ('..'),\nvfs_path_parent_lookup() detects this and immediately fails,\nreturning -EXDEV.\n\nHowever, a bug exists in __ksmbd_vfs_kern_path() under caseless mode.\nThe function fails to intercept the -EXDEV error and erroneously\nfalls through to the caseless retry logic, which is intended only\nfor genuinely missing files. During this retry process, the path\nis reconstructed, leading to an unintended LOOKUP_BENEATH bypass\nthat allows write-capable users to create zero-length files or\ndirectories outside the exported share.\n\nFix this by ensuring that the execution only proceeds to the caseless\nlookup retry when the error is specifically -ENOENT. Any other errors,\nsuch as -EXDEV from a path traversal attempt, must be returned immediately."}], "id": "CVE-2026-64400", "lastModified": "2026-10-30T13:19:36.180", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "HIGH", "baseScore": 8.6, "baseSeverity": "HIGH", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 4.7, "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary"}]}, "published": "2026-07-25T10:17:23.510", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/21f050439db157f2afcc19885dec14549ca6ffc0"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/54bab9ba5a9f156ffa9324fcbe5a356fd0242f95"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"], "url": "https://git.kernel.org/stable/c/8c9a4f1327eb71efbf14842e7b8a6d965077eb67"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/a1c331d98313380c38f616c8b28b890ec8ef9c28"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/cfb5a56c218888f9d74165dff0c282cd0be97983"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/eec1dd2586c4016b7555a5d047db2b3756459fb2"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Modified", "weaknesses": [{"description": [{"lang": "en", "value": "NVD-CWE-noinfo"}], "source": "nvd@nist.gov", "type": "Primary"}]}

{"bugzilla": {"description": "kernel: ksmbd: prevent path traversal bypass by restricting caseless retry", "id": "2507194", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2507194"}, "csaw": false, "cwe": "CWE-22", "details": ["A flaw was found in the Linux kernel's ksmbd component. A vulnerability in the ksmbd component allows a remote authenticated attacker to bypass path restrictions. Specifically, a bug in the caseless retry logic during path resolution fails to properly handle directory traversal attempts. This allows the attacker to create files or directories outside of the intended shared directory boundaries."], "name": "CVE-2026-64400", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Not affected", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}], "public_date": "2026-07-25T00:00:00Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-64400\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-64400\nhttps://lore.kernel.org/linux-cve-announce/2026072529-CVE-2026-64400-d372@gregkh/T"]}

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