FKIE_CVE-2026-31613

Vulnerability from fkie_nvd - Published: 2026-04-24 15:16 - Updated: 2026-04-24 17:51
Severity ?
Summary
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. 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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/781902e069f4ecb6c3b83502f181972c1446110a
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a66ef2e7ed837325c5600f8617d5ee0a0a149fdd
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e0dd90d14cbbf318157ea8e3fb62ee68a28655ed
Impacted products
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{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "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 \u003c\nend\", but reads p-\u003eErrorId at offset 4 and p-\u003eErrorDataLength 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-\u003eSymLinkErrorTag is read at offset 4 from\np-\u003eErrorContextData 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-\u003ePathBuffer 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."
    }
  ],
  "id": "CVE-2026-31613",
  "lastModified": "2026-04-24T17:51:40.810",
  "metrics": {},
  "published": "2026-04-24T15:16:40.560",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/781902e069f4ecb6c3b83502f181972c1446110a"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a66ef2e7ed837325c5600f8617d5ee0a0a149fdd"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e0dd90d14cbbf318157ea8e3fb62ee68a28655ed"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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