CVE-2026-53390 (GCVE-0-2026-53390)
Vulnerability from cvelistv5
Published
2026-07-19 12:01
Modified
2026-08-17 04:50
Severity ?
8.1 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix out-of-bounds read in smb_check_perm_dacl() The permission-check ACE walk in smb_check_perm_dacl() validates the ACE header size and caps sid.num_subauth at SID_MAX_SUB_AUTHORITIES, but it never checks that ace->size is actually large enough to contain num_subauth sub-authorities before compare_sids() dereferences them. CIFS_SID_BASE_SIZE covers the SID header up to but excluding the sub_auth[] array, and offsetof(struct smb_ace, sid) is the ACE header, so the existing guards only guarantee the 8-byte SID base, i.e. zero sub-authorities. compare_sids() then reads ace->sid.sub_auth[i] for i < min(local_sid->num_subauth, ace->sid.num_subauth). The local comparison SIDs (sid_everyone, sid_unix_NFS_mode, and the id_to_sid() result) always have at least one sub-authority, and an attacker controls the ACE revision and authority bytes (which lie within the in-bounds SID base), so they can match one of those SIDs and force the sub_auth read. A crafted ACE with size == 16 and num_subauth >= 1 placed at the tail of the security descriptor therefore causes a heap out-of-bounds read of up to SID_MAX_SUB_AUTHORITIES * sizeof(__le32) bytes past the pntsd allocation. The security descriptor is loaded by ksmbd_vfs_get_sd_xattr() into a buffer sized exactly to the on-disk data (kzalloc(sd_size) in ndr_decode_v4_ntacl()), so the read lands past the allocation. The malformed descriptor can be stored verbatim via SMB2_SET_INFO (the DACL is not normalised before being written to the security.NTACL xattr) and the read fires on a subsequent SMB2_CREATE access check, making this reachable by an authenticated client on a share that uses ACL xattrs. Add the missing num_subauth-versus-ace_size check, mirroring the identical guards already present in the sibling parsers parse_dacl() and smb_inherit_dacl().
References
Impacted products
Vendor Product Version
Linux Linux Version: 282cbbb476b9f35793452bc461934af4c7eca169
Version: f20adc4ef7428bc485ee83fd1a592252fb87718b
Version: 325d4ac11f526cb8964cff14548ccf02d8c756d8
Version: 95e5aa3c3261da8c95b27d7aecf8ee39b9f86a4c
Version: 90089584b2e25c4510b7b987387b4405f0673ece
Version: d07b26f39246a82399661936dd0c853983cfade7
Version: d07b26f39246a82399661936dd0c853983cfade7
Version: 151b1799861fde38087c08f613abc2843ef597b0
Version: 5.15.210   ≤
Version: 6.1.176   ≤
Version: 6.6.140   ≤
Version: 6.12.84   ≤
Version: 6.18.25   ≤
Version: 7.0.2   ≤
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{
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix out-of-bounds read in smb_check_perm_dacl()\n\nThe permission-check ACE walk in smb_check_perm_dacl() validates the ACE\nheader size and caps sid.num_subauth at SID_MAX_SUB_AUTHORITIES, but it\nnever checks that ace-\u003esize is actually large enough to contain\nnum_subauth sub-authorities before compare_sids() dereferences them.\n\nCIFS_SID_BASE_SIZE covers the SID header up to but excluding the\nsub_auth[] array, and offsetof(struct smb_ace, sid) is the ACE header,\nso the existing guards only guarantee the 8-byte SID base, i.e. zero\nsub-authorities. compare_sids() then reads ace-\u003esid.sub_auth[i] for\ni \u003c min(local_sid-\u003enum_subauth, ace-\u003esid.num_subauth). The local\ncomparison SIDs (sid_everyone, sid_unix_NFS_mode, and the id_to_sid()\nresult) always have at least one sub-authority, and an attacker controls\nthe ACE revision and authority bytes (which lie within the in-bounds SID\nbase), so they can match one of those SIDs and force the sub_auth read.\n\nA crafted ACE with size == 16 and num_subauth \u003e= 1 placed at the tail of\nthe security descriptor therefore causes a heap out-of-bounds read of up\nto SID_MAX_SUB_AUTHORITIES * sizeof(__le32) bytes past the pntsd\nallocation. The security descriptor is loaded by ksmbd_vfs_get_sd_xattr()\ninto a buffer sized exactly to the on-disk data (kzalloc(sd_size) in\nndr_decode_v4_ntacl()), so the read lands past the allocation. The\nmalformed descriptor can be stored verbatim via SMB2_SET_INFO (the DACL\nis not normalised before being written to the security.NTACL xattr) and\nthe read fires on a subsequent SMB2_CREATE access check, making this\nreachable by an authenticated client on a share that uses ACL xattrs.\n\nAdd the missing num_subauth-versus-ace_size check, mirroring the\nidentical guards already present in the sibling parsers parse_dacl() and\nsmb_inherit_dacl()."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug is reachable through ksmbd\u0027s in-kernel SMB2 server on TCP/445 via SMB2_SET_INFO (to store a crafted security descriptor) and SMB2_CREATE (to trigger the DACL walk), with packets handled from ksmbd_conn_handler_loop() through smb2_set_info()/smb2_open() into smb_check_perm_dacl().\nAC:L - An attacker fully controls the malformed ACE fields (size, num_subauth, revision, authority bytes) and can reliably place the ACE at the tail of a security descriptor, store it verbatim, then trigger the read on the next CREATE without depending on race timing or uncontrollable memory layout.\nPR:L - Exploitation requires a completed SMB2 session and share access: SMB2_SET_INFO needs FILE_WRITE_DAC/FILE_WRITE_OWNER on an open file, and the poisoned descriptor is only persisted on shares with ACL xattr support, which is authenticated low-privilege client access rather than pre-auth or host root.\nUI:N - No end-user action is required beyond the attacker sending crafted SMB2 protocol messages over the network; no victim must open a file, mount a share, or perform any interactive step.\nS:U - The vulnerability is confined to kernel heap memory reads during ksmbd DACL permission evaluation and does not cross a security boundary such as guest-to-host VM escape or sandbox escape.\nC:H - compare_sids() performs a heap out-of-bounds read of up to SID_MAX_SUB_AUTHORITIES (15) sub-authority dwords (60 bytes) past the kzalloc()-sized security descriptor buffer, exposing adjacent kernel heap contents even though the data is not returned in the SMB response.\nI:N - The flaw is a read-only out-of-bounds access in compare_sids() with no memory write, type confusion, or demonstrated control-flow hijack primitive; integrity is not directly compromised.\nA:H - Reading past the end of the kmalloc allocation can fault the kernel (oops/panic), and a malicious descriptor planted on a shared file can deny availability to any other authenticated client whose SMB2_CREATE triggers smb_check_perm_dacl()."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:50:41.549Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/c7488c85fd822959e9b5c22fbd9e7c8a21caf5e0"
        },
        {
          "url": "https://git.kernel.org/stable/c/988c93d3bba066d8669143e6ec30bb2be9608d53"
        },
        {
          "url": "https://git.kernel.org/stable/c/36599894fa8536fefdf1e296c0af71b8b7226859"
        },
        {
          "url": "https://git.kernel.org/stable/c/d5c81a095c86fe507c032d08f3a8cfc518444927"
        },
        {
          "url": "https://git.kernel.org/stable/c/7627ff8c4f9919f14de562b0160ab4ec9d80b1f7"
        },
        {
          "url": "https://git.kernel.org/stable/c/e36e35660adb9b8ef1435ac359151dda5f094c55"
        },
        {
          "url": "https://git.kernel.org/stable/c/1ef06004ed4bd6d3ed8c840d9d1a376b66d4935b"
        }
      ],
      "title": "ksmbd: fix out-of-bounds read in smb_check_perm_dacl()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-53390",
    "datePublished": "2026-07-19T12:01:54.951Z",
    "dateReserved": "2026-06-09T07:44:35.402Z",
    "dateUpdated": "2026-08-17T04:50:41.549Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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