{"cve":"CVE-2026-31712","nvd":{"published":"2026-05-01T14:16:21.270","modified":"2026-10-15T02:19:19.810","status":"Modified","description":"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 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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H","score":8.3},"cwes":["CWE-787"],"references":["https://git.kernel.org/stable/c/151b1799861fde38087c08f613abc2843ef597b0","https://git.kernel.org/stable/c/282cbbb476b9f35793452bc461934af4c7eca169","https://git.kernel.org/stable/c/325d4ac11f526cb8964cff14548ccf02d8c756d8","https://git.kernel.org/stable/c/90089584b2e25c4510b7b987387b4405f0673ece","https://git.kernel.org/stable/c/95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-19T22:33:09.003606135+00:00"},"epss":{"cve":"CVE-2026-31712","score":0.00323,"percentile":0.2507,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}