{"id":"CVE-2026-63909","state":"PUBLISHED","title":"ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops","description":"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().","publishedAt":"2026-07-19T14:55:15.060Z","updatedAt":"2026-08-05T12:37:02.949Z","severity":{"score":8.1,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"282cbbb476b9f35793452bc461934af4c7eca169","status":"affected","lessThan":"5500ba1d410aed1eded3eb04a76b10cfb4409334","versionType":"git"},{"version":"f20adc4ef7428bc485ee83fd1a592252fb87718b","status":"affected","lessThan":"f6324b4240cf0b26a84c33f68a1222d727ff4af2","versionType":"git"},{"version":"325d4ac11f526cb8964cff14548ccf02d8c756d8","status":"affected","lessThan":"0fe08c5776a798f46df1fd74b331be26bdd644d6","versionType":"git"},{"version":"95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c","status":"affected","lessThan":"d333af32e4451285e427f2d9c29de3a39f6f6d48","versionType":"git"},{"version":"90089584b2e25c4510b7b987387b4405f0673ece","status":"affected","lessThan":"94215d55b09445993929f4fc966061d61de74929","versionType":"git"},{"version":"151b1799861fde38087c08f613abc2843ef597b0","status":"affected","lessThan":"4f7c131d2bdd7cd64b96f60d10be5ea72253f520","versionType":"git"},{"version":"d07b26f39246a82399661936dd0c853983cfade7","status":"affected","lessThan":"0e60dafe97eca61721f3db456f97d97a80c6c8ae","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/smbacl.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6.6.140","status":"affected","lessThan":"6.6.143","versionType":"semver"},{"version":"6.12.84","status":"affected","lessThan":"6.12.93","versionType":"semver"},{"version":"6.18.25","status":"affected","lessThan":"6.18.35","versionType":"semver"},{"version":"7.0.2","status":"affected","lessThan":"7.0.12","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/smbacl.c"]}],"references":["https://git.kernel.org/stable/c/5500ba1d410aed1eded3eb04a76b10cfb4409334","https://git.kernel.org/stable/c/f6324b4240cf0b26a84c33f68a1222d727ff4af2","https://git.kernel.org/stable/c/0fe08c5776a798f46df1fd74b331be26bdd644d6","https://git.kernel.org/stable/c/d333af32e4451285e427f2d9c29de3a39f6f6d48","https://git.kernel.org/stable/c/94215d55b09445993929f4fc966061d61de74929","https://git.kernel.org/stable/c/4f7c131d2bdd7cd64b96f60d10be5ea72253f520","https://git.kernel.org/stable/c/0e60dafe97eca61721f3db456f97d97a80c6c8ae"],"weaknesses":[],"ingestedAt":"2026-10-29T20:12:41.951Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/63xxx/CVE-2026-63909.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-63909","state":"PUBLISHED","datePublished":"2026-07-19T14:55:15.060Z","dateUpdated":"2026-08-05T12:37:02.949Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-07-19T07:54:57.020Z"},"containers":{"cna":{"title":"ksmbd: OOB read regression in smb_check_perm_dacl() ACE-walk loops","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()."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"282cbbb476b9f35793452bc461934af4c7eca169","status":"affected","lessThan":"5500ba1d410aed1eded3eb04a76b10cfb4409334","versionType":"git"},{"version":"f20adc4ef7428bc485ee83fd1a592252fb87718b","status":"affected","lessThan":"f6324b4240cf0b26a84c33f68a1222d727ff4af2","versionType":"git"},{"version":"325d4ac11f526cb8964cff14548ccf02d8c756d8","status":"affected","lessThan":"0fe08c5776a798f46df1fd74b331be26bdd644d6","versionType":"git"},{"version":"95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c","status":"affected","lessThan":"d333af32e4451285e427f2d9c29de3a39f6f6d48","versionType":"git"},{"version":"90089584b2e25c4510b7b987387b4405f0673ece","status":"affected","lessThan":"94215d55b09445993929f4fc966061d61de74929","versionType":"git"},{"version":"151b1799861fde38087c08f613abc2843ef597b0","status":"affected","lessThan":"4f7c131d2bdd7cd64b96f60d10be5ea72253f520","versionType":"git"},{"version":"d07b26f39246a82399661936dd0c853983cfade7","status":"affected","lessThan":"0e60dafe97eca61721f3db456f97d97a80c6c8ae","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/smbacl.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"6.6.140","status":"affected","lessThan":"6.6.143","versionType":"semver"},{"version":"6.12.84","status":"affected","lessThan":"6.12.93","versionType":"semver"},{"version":"6.18.25","status":"affected","lessThan":"6.18.35","versionType":"semver"},{"version":"7.0.2","status":"affected","lessThan":"7.0.12","versionType":"semver"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/smb/server/smbacl.c"]}],"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"}],"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."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:37:02.949Z"},"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"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}