{"id":"CVE-2026-31712","title":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: require minimum ACE size in smb_check_perm_dacl()\n\nBoth ACE-walk loops in smb_check_perm_dacl() only guard against an\nunder-sized remaining buffer, not against a…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: require minimum ACE size in smb_check_perm_dacl()\n\nBoth ACE-walk loops in smb_check_perm_dacl() only guard against an\nunder-sized remaining buffer, not against a…","severity":"high","cvss":8.3,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H","cwe":["CWE-787"],"vendor":"linux","product":"linux_kernel","affected":["linux_kernel >= 5.15, < 6.12.84","linux_kernel >= 6.13, < 6.18.25","linux_kernel >= 6.19, < 7.0.2"],"patched":["linux_kernel 7.0.2"],"published":"2026-05-01","updated":"2026-10-15","sourceUpdated":"2026-10-15T02:19:19.810","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-31712","references":[{"url":"https://git.kernel.org/stable/c/151b1799861fde38087c08f613abc2843ef597b0","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/282cbbb476b9f35793452bc461934af4c7eca169","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/325d4ac11f526cb8964cff14548ccf02d8c756d8","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/90089584b2e25c4510b7b987387b4405f0673ece","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/d07b26f39246a82399661936dd0c853983cfade7","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/f20adc4ef7428bc485ee83fd1a592252fb87718b","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://cert-portal.siemens.com/productcert/html/ssa-784472.html","label":"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e"}],"tags":["nvd","cve.org"],"epss":0.00315,"epssPercentile":0.2278,"ingestedAt":"2026-10-15T03:30:12.868Z","slug":"CVE-2026-31712","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: require minimum ACE size in smb_check_perm_dacl()\n\nBoth ACE-walk loops in smb_check_perm_dacl() only guard against an\nunder-sized remaining buffer, not against an ACE whose declared\n`ace->size` is smaller than the struct it claims to describe:\n\n  if (offsetof(struct smb_ace, access_req) > aces_size)\n      break;\n  ace_size = le16_to_cpu(ace->size);\n  if (ace_size > aces_size)\n      break;\n\nThe first check only requires the 4-byte ACE header to be in bounds;\nit does not require access_req (4 bytes at offset 4) to be readable.\nAn attacker who has set a crafted DACL on a file they own can declare\nace->size == 4 with aces_size == 4, pass both checks, and then\n\n  granted |= le32_to_cpu(ace->access_req);               /* upper loop */\n  compare_sids(&sid, &ace->sid);                         /* lower loop */\n\nreads access_req at offset 4 (OOB by up to 4 bytes) and ace->sid at\noffset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES\n* 4 bytes).\n\nTighten both loops to require\n\n  ace_size >= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE\n\nwhich is the smallest valid on-wire ACE layout (4-byte header +\n4-byte access_req + 8-byte sid base with zero sub-auths).  Also\nreject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES\nbefore letting compare_sids() dereference sub_auth[] entries.\n\nparse_sec_desc() already enforces an equivalent check (lines 441-448);\nsmb_check_perm_dacl() simply grew weaker validation over time.\n\nReachability: authenticated SMB client with permission to set an ACL\non a file.  On a subsequent CREATE against that file, the kernel\nwalks the stored DACL via smb_check_perm_dacl() and triggers the\nOOB read.  Not pre-auth, and the OOB read is not reflected to the\nattacker, but KASAN reports and kernel state corruption are\npossible.\n\n## Affected\n\n- `linux_kernel >= 5.15, < 6.12.84`\n- `linux_kernel >= 6.13, < 6.18.25`\n- `linux_kernel >= 6.19, < 7.0.2`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `linux_kernel 7.0.2`","depth":"twilight","depthScore":46,"depthScoreParts":{"impact":45.7,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}