CVE-2026-31613

Estado: ModificadaAlta (8.1)—

In the Linux kernel, the following vulnerability has been resolved:

smb: client: fix OOB reads parsing symlink error response

When a CREATE returns STATUS_STOPPED_ON_SYMLINK, smb2_check_message() returns success without any length validation, leaving the symlink parsers as the only defense against an untrusted server.

symlink_data() walks SMB 3.1.1 error contexts with the loop test "p < end", but reads p->ErrorId at offset 4 and p->ErrorDataLength at offset 0. When the server-controlled ErrorDataLength advances p to within 1-7 bytes of end, the next iteration will read past it. When the matching context is found, sym->SymLinkErrorTag is read at offset 4 from p->ErrorContextData with no check that the symlink header itself fits.

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smb2_parse_symlink_response() then bounds-checks the substitute name using SMB2_SYMLINK_STRUCT_SIZE as the offset of PathBuffer from iov_base. That value is computed as sizeof(smb2_err_rsp) + sizeof(smb2_symlink_err_rsp), which is correct only when ErrorContextCount == 0.

With at least one error context the symlink data sits 8 bytes deeper, and each skipped non-matching context shifts it further by 8 + ALIGN(ErrorDataLength, 8). The check is too short, allowing the substitute name read to run past iov_len. The out-of-bound heap bytes are UTF-16-decoded into the symlink target and returned to userspace via readlink(2).

Fix this all up by making the loops test require the full context header to fit, rejecting sym if its header runs past end, and bound the substitute name against the actual position of sym->PathBuffer rather than a fixed offset.

Because sub_offs and sub_len are 16bits, the pointer math will not overflow here with the new greater-than.

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H
Puntuación base: 8.1

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.55%
Percentil entre todas las CVEs puntuadas: 44
Fecha de la puntuación: 6/10/2026

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1203 Exploitation for Client Executionexecution75 %
Impacto principalT1005 Data from Local Systemcollection85 %
Impacto secundarioT1499.004 Application or System Exploitationimpact60 %

Vector CVSS con UI:R requiere interacción (abrir archivo SMB preparado). Lectura OOB en parsing de respuesta de symlink expone bytes heap a userspace vía readlink(2). DoS potencial por corrupción de memoria.

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Filter Network Traffic Application Isolation and Sandboxing Exploit Protection Update Software Data Loss Prevention

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

CWE-125

Referencias

JSON original (NVD)

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsmb: client: fix OOB reads parsing symlink error response\n\nWhen a CREATE returns STATUS_STOPPED_ON_SYMLINK, smb2_check_message()\nreturns success without any length validation, leaving the symlink\nparsers as the only defense against an untrusted server.\n\nsymlink_data() walks SMB 3.1.1 error contexts with the loop test \"p <\nend\", but reads p->ErrorId at offset 4 and p->ErrorDataLength at offset\n0.  When the server-controlled ErrorDataLength advances p to within 1-7\nbytes of end, the next iteration will read past it.  When the matching\ncontext is found, sym->SymLinkErrorTag is read at offset 4 from\np->ErrorContextData with no check that the symlink header itself fits.\n\nsmb2_parse_symlink_response() then bounds-checks the substitute name\nusing SMB2_SYMLINK_STRUCT_SIZE as the offset of PathBuffer from\niov_base.  That value is computed as sizeof(smb2_err_rsp) +\nsizeof(smb2_symlink_err_rsp), which is correct only when\nErrorContextCount == 0.\n\nWith at least one error context the symlink data sits 8 bytes deeper,\nand each skipped non-matching context shifts it further by 8 +\nALIGN(ErrorDataLength, 8).  The check is too short, allowing the\nsubstitute name read to run past iov_len.  The out-of-bound heap bytes\nare UTF-16-decoded into the symlink target and returned to userspace via\nreadlink(2).\n\nFix this all up by making the loops test require the full context header\nto fit, rejecting sym if its header runs past end, and bound the\nsubstitute name against the actual position of sym->PathBuffer rather\nthan a fixed offset.\n\nBecause sub_offs and sub_len are 16bits, the pointer math will not\noverflow here with the new greater-than."
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