{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-63909", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.020Z", "datePublished": "2026-07-19T14:55:15.060Z", "dateUpdated": "2026-08-05T12:37:02.949Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:37:02.949Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops\n\nCommit d07b26f39246 (\"ksmbd: require minimum ACE size in\nsmb_check_perm_dacl()\") introduced a transposed bounds check:\n\n if (offsetof(struct smb_ace, sid) + aces_size < CIFS_SID_BASE_SIZE)\n\nSince offsetof(..sid) is 8 and CIFS_SID_BASE_SIZE is 8, this evaluates\nto `aces_size < 0`. Because `aces_size` is always non-negative, this\ncheck becomes dead code and never breaks the loop.\n\nWorse, that commit removed the old 4-byte guard, meaning the loop now\nreads `ace->size` (offset 2) even when `aces_size` is 0-3 bytes. This\nre-opens a 2-byte heap out-of-bounds (OOB) read past the pntsd allocation\nduring subsequent SMB2_CREATE operations.\n\nFix this by properly transposing the comparison to require at least\n16 bytes (8-byte offset + 8-byte SID base), matching the correct form\nused in smb_inherit_dacl()." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H", "baseScore": 8.1, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:N - The bug is reachable through ksmbd's in-kernel SMB server on TCP port 445; a remote attacker sends crafted SMB2 packets that traverse the normal network receive path to smb_check_perm_dacl().\nAC:L - The attacker fully controls the crafted NTSD/DACL planted via SMB and the subsequent SMB2_CREATE that triggers the walk; no race or victim-specific memory layout is required beyond standard heap behavior.\nPR:L - Exploitation requires an authenticated SMB2 session (post SESSION_SETUP and TREE_CONNECT) with permission to create files and set security descriptors (WRITE_DAC) on a share with ACL xattr support; this is a low-privileged authenticated user, not an unauthenticated attacker.\nUI:N - No end-user interaction is required beyond the attacker operating their own SMB client against an exposed ksmbd server.\nS:U - The vulnerability is a kernel heap out-of-bounds read within ksmbd's own security context; it does not cross a VM, sandbox, or IOMMU security boundary.\nC:H - The bug is an out-of-bounds heap read of ace->size past the pntsd kmalloc allocation; per kernel guidance OOB reads warrant High confidentiality impact as adjacent heap metadata or pointers may be disclosed.\nI:N - This is a read-only out-of-bounds access with no memory write, type confusion, or demonstrated ability to modify kernel data or achieve code execution through the corrupted read path.\nA:H - Reading beyond the kmalloc boundary can trigger a kernel page fault, oops, or panic; the original fix commit also notes KASAN reports and possible kernel state corruption from the OOB access." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/smb/server/smbacl.c" ], "versions": [ { "version": "282cbbb476b9f35793452bc461934af4c7eca169", "lessThan": "5500ba1d410aed1eded3eb04a76b10cfb4409334", "status": "affected", "versionType": "git" }, { "version": "f20adc4ef7428bc485ee83fd1a592252fb87718b", "lessThan": "f6324b4240cf0b26a84c33f68a1222d727ff4af2", "status": "affected", "versionType": "git" }, { "version": "325d4ac11f526cb8964cff14548ccf02d8c756d8", "lessThan": "0fe08c5776a798f46df1fd74b331be26bdd644d6", "status": "affected", "versionType": "git" }, { "version": "95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c", "lessThan": "d333af32e4451285e427f2d9c29de3a39f6f6d48", "status": "affected", "versionType": "git" }, { "version": "90089584b2e25c4510b7b987387b4405f0673ece", "lessThan": "94215d55b09445993929f4fc966061d61de74929", "status": "affected", "versionType": "git" }, { "version": "151b1799861fde38087c08f613abc2843ef597b0", "lessThan": "4f7c131d2bdd7cd64b96f60d10be5ea72253f520", "status": "affected", "versionType": "git" }, { "version": "d07b26f39246a82399661936dd0c853983cfade7", "lessThan": "0e60dafe97eca61721f3db456f97d97a80c6c8ae", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/smb/server/smbacl.c" ], "versions": [ { "version": "6.6.140", "lessThan": "6.6.143", "status": "affected", "versionType": "semver" }, { "version": "6.12.84", "lessThan": "6.12.93", "status": "affected", "versionType": "semver" }, { "version": "6.18.25", "lessThan": "6.18.35", "status": "affected", "versionType": "semver" }, { "version": "7.0.2", "lessThan": "7.0.12", "status": "affected", "versionType": "semver" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.6.140", "versionEndExcluding": "6.6.143" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.12.84", "versionEndExcluding": "6.12.93" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.18.25", "versionEndExcluding": "6.18.35" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.0.2", "versionEndExcluding": "7.0.12" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334" }, { "url": "https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2" }, { "url": "https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6" }, { "url": "https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48" }, { "url": "https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929" }, { "url": "https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520" }, { "url": "https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae" } ], "title": "ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops", "x_generator": { "engine": "bippy-1.2.0" } } } }