Authentication Bypass Using an Alternate Path or Channel

A product requires authentication, but the product has an alternate path or channel that does not require authentication.


The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

Register SECURE_ME is located at address 0xF00. A mirror of this register called COPY_OF_SECURE_ME is at location 0x800F00. The register SECURE_ME is protected from malicious agents and only allows access to select, while COPY_OF_SECURE_ME is not.

Access control is implemented using an allowlist (as indicated by acl_oh_allowlist). The identity of the initiator of the transaction is indicated by the one hot input, incoming_id. This is checked against the acl_oh_allowlist (which contains a list of initiators that are allowed to access the asset).

Though this example is shown in Verilog, it will apply to VHDL as well.

module foo_bar(data_out, data_in, incoming_id, address, clk, rst_n);
output [31:0] data_out;
input [31:0] data_in, incoming_id, address;
input clk, rst_n;
wire write_auth, addr_auth;
reg [31:0] data_out, acl_oh_allowlist, q;
assign write_auth = | (incoming_id & acl_oh_allowlist) ? 1 : 0;
always @*

  acl_oh_allowlist <= 32'h8312;

assign addr_auth = (address == 32'hF00) ? 1: 0;
always @ (posedge clk or negedge rst_n)

  if (!rst_n)


      q <= 32'h0;
      data_out <= 32'h0;




      q <= (addr_auth & write_auth) ? data_in: q;
      data_out <= q;



assign addr_auth = (address == 32'hF00) ? 1: 0;

The bugged line of code is repeated in the Bad example above. Weakness arises from the fact that the SECURE_ME register can be modified by writing to the shadow register COPY_OF_SECURE_ME, the address of COPY_OF_SECURE_ME should also be included in the check. That buggy line of code should instead be replaced as shown in the Good Code Snippet below.

assign addr_auth = (address == 32'hF00 || address == 32'h800F00) ? 1: 0;

See Also

Comprehensive Categorization: Access Control

Weaknesses in this category are related to access control.

ICS Communications: Zone Boundary Failures

Weaknesses in this category are related to the "Zone Boundary Failures" category from the SEI ETF "Categories of Security Vulnerabilities in ICS" as published in March...

OWASP Top Ten 2021 Category A07:2021 - Identification and Authentication Failures

Weaknesses in this category are related to the A07 category "Identification and Authentication Failures" in the OWASP Top Ten 2021.

Comprehensive CWE Dictionary

This view (slice) covers all the elements in CWE.

Weaknesses Introduced During Design

This view (slice) lists weaknesses that can be introduced during design.

Weakness Base Elements

This view (slice) displays only weakness base elements.

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