CVE-2026-31706

{"id": "CVE-2026-31706", "cveTags": [], "metrics": {"cvssMetricV31": [{"type": "Secondary", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "cvssData": {"scope": "UNCHANGED", "version": "3.1", "baseScore": 8.8, "attackVector": "NETWORK", "baseSeverity": "HIGH", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "integrityImpact": "HIGH", "userInteraction": "NONE", "attackComplexity": "LOW", "availabilityImpact": "HIGH", "privilegesRequired": "LOW", "confidentialityImpact": "HIGH"}, "impactScore": 5.9, "exploitabilityScore": 2.8}]}, "affected": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "affectedData": [{"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9", "lessThan": "4d37830c2c834987de329d58fb9a319067400361", "versionType": "git"}, {"status": "affected", "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9", "lessThan": "ad7d18df7423c522ed9dc7e33bd5d54c66b1bc37", "versionType": "git"}, {"status": "affected", "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9", "lessThan": "063a7409b0de46d7c770b65bb0338e6fdb3b1f0a", "versionType": "git"}, {"status": "affected", "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9", "lessThan": "3e5360b422dd741cb315654a191fa73869a37414", "versionType": "git"}, {"status": "affected", "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9", "lessThan": "59c32abaaec9cdd6164811c7e864e72f7554b82d", "versionType": "git"}, {"status": "affected", "version": "e2f34481b24db2fd634b5edb0a5bd0e4d38cc6e9", "lessThan": "3e4e2ea2a781018ed5d75f969e3e5606beb66e48", "versionType": "git"}], "programFiles": ["fs/smb/server/smbacl.c"], "defaultStatus": "unaffected"}, {"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "product": "Linux", "versions": [{"status": "affected", "version": "5.15"}, {"status": "unaffected", "version": "0", "lessThan": "5.15", "versionType": "semver"}, {"status": "unaffected", "version": "6.1.191", "versionType": "semver", "lessThanOrEqual": "6.1.*"}, {"status": "unaffected", "version": "6.6.160", "versionType": "semver", "lessThanOrEqual": "6.6.*"}, {"status": "unaffected", "version": "6.12.84", "versionType": "semver", "lessThanOrEqual": "6.12.*"}, {"status": "unaffected", "version": "6.18.25", "versionType": "semver", "lessThanOrEqual": "6.18.*"}, {"status": "unaffected", "version": "7.0.2", "versionType": "semver", "lessThanOrEqual": "7.0.*"}, {"status": "unaffected", "version": "7.1", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*"}], "programFiles": ["fs/smb/server/smbacl.c"], "defaultStatus": "affected"}]}], "published": "2026-05-01T14:16:20.597", "references": [{"url": "https://git.kernel.org/stable/c/063a7409b0de46d7c770b65bb0338e6fdb3b1f0a", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/3e4e2ea2a781018ed5d75f969e3e5606beb66e48", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/3e5360b422dd741cb315654a191fa73869a37414", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/4d37830c2c834987de329d58fb9a319067400361", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/59c32abaaec9cdd6164811c7e864e72f7554b82d", "tags": ["Patch"], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/ad7d18df7423c522ed9dc7e33bd5d54c66b1bc37", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "vulnStatus": "Modified", "weaknesses": [{"type": "Primary", "source": "nvd@nist.gov", "description": [{"lang": "en", "value": "NVD-CWE-noinfo"}]}], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: validate num_aces and harden ACE walk in smb_inherit_dacl()\n\nsmb_inherit_dacl() trusts the on-disk num_aces value from the parent\ndirectory's DACL xattr and uses it to size a heap allocation:\n\n aces_base = kmalloc(sizeof(struct smb_ace) * num_aces * 2, ...);\n\nnum_aces is a u16 read from le16_to_cpu(parent_pdacl->num_aces)\nwithout checking that it is consistent with the declared pdacl_size.\nAn authenticated client whose parent directory's security.NTACL is\ntampered (e.g. via offline xattr corruption or a concurrent path that\nbypasses parse_dacl()) can present num_aces = 65535 with minimal\nactual ACE data. This causes a ~8 MB allocation (not kzalloc, so\nuninitialized) that the subsequent loop only partially populates, and\nmay also overflow the three-way size_t multiply on 32-bit kernels.\n\nAdditionally, the ACE walk loop uses the weaker\noffsetof(struct smb_ace, access_req) minimum size check rather than\nthe minimum valid on-wire ACE size, and does not reject ACEs whose\ndeclared size is below the minimum.\n\nReproduced on UML + KASAN + LOCKDEP against the real ksmbd code path.\nA legitimate mount.cifs client creates a parent directory over SMB\n(ksmbd writes a valid security.NTACL xattr), then the NTACL blob on\nthe backing filesystem is rewritten to set num_aces = 0xFFFF while\nkeeping the posix_acl_hash bytes intact so ksmbd_vfs_get_sd_xattr()'s\nhash check still passes. A subsequent SMB2 CREATE of a child under\nthat parent drives smb2_open() into smb_inherit_dacl() (share has\n\"vfs objects = acl_xattr\" set), which fails the page allocator:\n\n WARNING: mm/page_alloc.c:5226 at __alloc_frozen_pages_noprof+0x46c/0x9c0\n Workqueue: ksmbd-io handle_ksmbd_work\n __alloc_frozen_pages_noprof+0x46c/0x9c0\n ___kmalloc_large_node+0x68/0x130\n __kmalloc_large_node_noprof+0x24/0x70\n __kmalloc_noprof+0x4c9/0x690\n smb_inherit_dacl+0x394/0x2430\n smb2_open+0x595d/0xabe0\n handle_ksmbd_work+0x3d3/0x1140\n\nWith the patch applied the added guard rejects the tampered value\nwith -EINVAL before any large allocation runs, smb2_open() falls back\nto smb2_create_sd_buffer(), and the child is created with a default\nSD. No warning, no splat.\n\nFix by:\n\n 1. Validating num_aces against pdacl_size using the same formula\n applied in parse_dacl().\n\n 2. Replacing the raw kmalloc(sizeof * num_aces * 2) with\n kmalloc_array(num_aces * 2, sizeof(...)) for overflow-safe\n allocation.\n\n 3. Tightening the per-ACE loop guard to require the minimum valid\n ACE size (offsetof(smb_ace, sid) + CIFS_SID_BASE_SIZE) and\n rejecting under-sized ACEs, matching the hardening in\n smb_check_perm_dacl() and parse_dacl().\n\nv1 -> v2:\n - Replace the synthetic test-module splat in the changelog with a\n real-path UML + KASAN reproduction driven through mount.cifs and\n SMB2 CREATE; Namjae flagged the kcifs3_test_inherit_dacl_old name\n in v1 since it does not exist in ksmbd.\n - Drop the commit-hash citation from the code comment per Namjae's\n review; keep the parse_dacl() pointer."}, {"lang": "es", "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta: ksmbd: validar num_aces y reforzar el recorrido de ACE en smb_inherit_dacl() smb_inherit_dacl() conf\u00eda en el valor num_aces en disco del xattr DACL del directorio padre y lo usa para dimensionar una asignaci\u00f3n de pila: aces_base = kmalloc(sizeof(struct smb_ace) * num_aces * 2, ...); num_aces es un u16 le\u00eddo de le16_to_cpu(parent_pdacl -> num_aces) sin verificar que sea consistente con el pdacl_size declarado. Un cliente autenticado cuyo security.NTACL del directorio padre ha sido manipulado (por ejemplo, mediante corrupci\u00f3n de xattr fuera de l\u00ednea o una ruta concurrente que omite parse_dacl()) puede presentar num_aces = 65535 con datos ACE reales m\u00ednimos. Esto causa una asignaci\u00f3n de ~8 MB (no kzalloc, por lo tanto no inicializada) que el bucle subsiguiente solo rellena parcialmente, y tambi\u00e9n puede desbordar la multiplicaci\u00f3n size_t de tres v\u00edas en kernels de 32 bits. Adem\u00e1s, el bucle de recorrido de ACE usa la verificaci\u00f3n de tama\u00f1o m\u00ednimo m\u00e1s d\u00e9bil offsetof(struct smb_ace, access_req) en lugar del tama\u00f1o m\u00ednimo v\u00e1lido de ACE en la red, y no rechaza los ACEs cuyo tama\u00f1o declarado est\u00e1 por debajo del m\u00ednimo. Reproducido en UML + KASAN + LOCKDEP contra la ruta de c\u00f3digo real de ksmbd. Un cliente mount.cifs leg\u00edtimo crea un directorio padre sobre SMB (ksmbd escribe un xattr security.NTACL v\u00e1lido), luego el blob NTACL en el sistema de archivos de respaldo es reescrito para establecer num_aces = 0x FFFF mientras mantiene intactos los bytes posix_acl_hash para que la verificaci\u00f3n de hash de ksmbd_vfs_get_sd_xattr() a\u00fan pase. Un SMB2 CREATE subsiguiente de un hijo bajo ese padre lleva a smb2_open() a smb_inherit_dacl() (el recurso compartido tiene \u2019vfs objects = acl_xattr\u2019 configurado), lo que hace fallar al asignador de p\u00e1ginas: WARNING: mm/page_alloc.c:5226 at __alloc_frozen_pages_noprof+0x46c/0x9c0 Workqueue: ksmbd-io handle_ksmbd_work __alloc_frozen_pages_noprof+0x46c/0x9c0 ___kmalloc_large_node+0x68/0x130 __kmalloc_large_node_noprof+0x24/0x70 __kmalloc_noprof+0x4c9/0x690 smb_inherit_dacl+0x394/0x 2430 smb2_open+0x 595d/0x abe0 handle_ksmbd_work+0x3d3/0x 1140 Con el parche aplicado, la protecci\u00f3n a\u00f1adida rechaza el valor manipulado con -EINVAL antes de que se ejecute cualquier asignaci\u00f3n grande, smb2_open() recurre a smb2_create_sd_buffer(), y el hijo se crea con un SD predeterminado. Sin advertencia, sin error. Soluci\u00f3n mediante: 1. Validar num_aces contra pdacl_size usando la misma f\u00f3rmula aplicada en parse_dacl(). 2. Reemplazar el kmalloc(sizeof * num_aces * 2) en bruto con kmalloc_array(num_aces * 2, sizeof(...)) para una asignaci\u00f3n segura contra desbordamientos. 3. Ajustar la protecci\u00f3n del bucle por ACE para requerir el tama\u00f1o m\u00ednimo v\u00e1lido de ACE (offsetof(smb_ace, sid) + CIFS_SID_BASE_SIZE) y rechazar los ACEs de tama\u00f1o insuficiente, coincidiendo con el refuerzo en smb_check_perm_dacl() y parse_dacl(). v1 -mayor que v2: - Reemplazar el error del m\u00f3dulo de prueba sint\u00e9tico en el registro de cambios con una reproducci\u00f3n de ruta real de UML + KASAN impulsada a trav\u00e9s de mount.cifs y SMB2 CREATE; Namjae se\u00f1al\u00f3 el nombre kcifs3_test_inherit_dacl_old en v1 ya que no existe en ksmbd. - Eliminar la cita del hash de commit del comentario del c\u00f3digo seg\u00fan la revisi\u00f3n de Namjae; mantener el puntero de parse_dacl()."}], "lastModified": "2026-11-11T21:10:00.200", "configurations": [{"nodes": [{"negate": false, "cpeMatch": [{"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "04651641-C387-4546-B02F-17BA989CC253", "versionEndExcluding": "6.12.84", "versionStartIncluding": "5.15"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "8B0A7E0E-F6D8-45DB-8CD9-01839FE40A6C", "versionEndExcluding": "6.18.25", "versionStartIncluding": "6.13"}, {"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "vulnerable": true, "matchCriteriaId": "1BD58F1E-7C20-4C0D-92A2-FAC5CBFBE8A8", "versionEndExcluding": "7.0.2", "versionStartIncluding": "6.19"}], "operator": "OR"}]}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}