273 lines
15 KiB
JSON
273 lines
15 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-31712",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2026-03-09T15:48:24.133Z",
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"datePublished": "2026-05-01T13:56:08.583Z",
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"dateUpdated": "2026-10-15T01:18:08.369Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-08-05T12:24:46.463Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "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."
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:H",
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"baseScore": 8.3,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:N - ksmbd is an in-kernel SMB server reachable over the network via SMB2/SMB3 requests, typically TCP/445. The vulnerable DACL walk is reached from remote SMB CREATE processing after a crafted stored ACL is present.\nAC:L - No race or uncontrollable timing is required; an attacker can set a malformed DACL and then trigger a subsequent CREATE against that file. ACL xattr support is a reasonable ksmbd deployment configuration, not an exploit-complexity barrier.\nPR:L - The path is not pre-authentication: SMB2 commands require a valid authenticated session and tree connect. The attacker needs ordinary SMB credentials with permission to set an ACL on a file they control, not kernel/root privileges.\nUI:N - After authentication, the attacker can send the ACL-setting and CREATE requests directly. No victim user action is required.\nS:U - The impact remains within the kernel/ksmbd host security authority. There is no VM, IOMMU, or sandbox boundary crossing.\nC:H - The bug causes attacker-triggered out-of-bounds reads from kernel heap data beyond the stored security descriptor, including SID fields. Although not directly reflected, this is more than a strictly bounded few-byte read and the higher-severity rule makes High appropriate.\nI:L - The out-of-bounds data is consumed as permission-check state such as ACE access bits, so it can corrupt ksmbd access-control decisions for the requested object. There is no clear arbitrary kernel write or control-flow hijack primitive, so the integrity impact is limited rather than High.\nA:H - The malformed ACE can reliably trigger kernel out-of-bounds reads during SMB CREATE, producing KASAN reports and possible kernel oops/panic depending on configuration. A remote authenticated user can repeat the trigger for denial of service."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"fs/smb/server/smbacl.c"
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],
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"fs/smb/server/smbacl.c"
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],
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"lessThanOrEqual": "5.15.*",
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},
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},
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"version": "7.1",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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}
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],
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"title": "ksmbd: require minimum ACE size in smb_check_perm_dacl()",
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"dateUpdated": "2026-10-15T01:18:08.369Z"
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