CWE-1280: Access Control Check Implemented After Asset is Accessed

What is Access Control Check Implemented After Asset is Accessed?

• Overview: Access Control Check Implemented After Asset is Accessed (CWE-1280) is a vulnerability where a system performs access control checks after an asset (such as data or a resource) has already been accessed, instead of before. This can lead to unauthorized access if the check fails.

• Exploitation Methods:

• Attackers can exploit this vulnerability by accessing the asset before the access control check is completed, potentially bypassing any restrictions.
• Common attack patterns include timing attacks where the attacker rapidly accesses the asset before the access control check happens.

• Security Impact:

• Direct consequences include unauthorized access to sensitive data or resources.
• Potential cascading effects involve further exploitation, leading to data breaches or system compromise.
• Business impact can be severe, resulting in loss of customer trust, financial penalties, and legal liabilities.

• Prevention Guidelines:

• Specific code-level fixes include ensuring that access control checks are atomic, meaning they occur immediately and completely before any access to the asset.
• Security best practices involve rigorous testing and validation of access control mechanisms to ensure they run before asset access.
• Recommended tools and frameworks include using security-focused design patterns and tools that verify the timing and order of access control checks, such as static analysis tools for hardware description languages.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Verilog, VHDL, Not Language-Specific

Affected Technologies: Not Technology-Specific

Vulnerable Code Example

// Vulnerable code demonstrating access control check after asset access
module MemoryAccess (
    input wire clk,
    input wire [3:0] addr,
    input wire [7:0] data_in,
    input wire write_enable,
    input wire [3:0] user_access_level,
    output reg [7:0] data_out
);
    reg [7:0] memory [0:15];

    always @(posedge clk) begin
        // Memory access occurs before verifying user access level
        if (write_enable) begin
            memory[addr] <= data_in;  // Memory is written to without checking access level
        end
        data_out <= memory[addr];  // Memory is read without checking access level

        // Access control check is implemented after memory access
        if (user_access_level < 4) begin
            // Log unauthorized access attempt
            \$display("Unauthorized access attempt detected at address: %d", addr);
        end
    end
endmodule

In this vulnerable example, the memory is accessed before verifying if the user has the appropriate access level. This could lead to unauthorized users reading or modifying sensitive data, as the access control check is performed after the memory operation.

How to fix Access Control Check Implemented After Asset is Accessed?

To fix this vulnerability, the access control check must be performed before any memory operations. This ensures that only authorized users can read or modify the memory.

The fix involves:

1. Checking the user's access level before any memory operation.
2. Blocking memory read or write operations if the user does not have sufficient access level.
3. Logging unauthorized access attempts and returning a default value to prevent data leakage.

Fixed Code Example

// Fixed code with access control check implemented before asset access
module MemoryAccess (
    input wire clk,
    input wire [3:0] addr,
    input wire [7:0] data_in,
    input wire write_enable,
    input wire [3:0] user_access_level,
    output reg [7:0] data_out
);
    reg [7:0] memory [0:15];

    always @(posedge clk) begin
        // Implement access control check before any memory access
        if (user_access_level >= 4) begin
            // Only allow memory operations if access level is sufficient
            if (write_enable) begin
                memory[addr] <= data_in;  // Write to memory only if access level is adequate
            end
            data_out <= memory[addr];  // Read from memory only if access level is adequate
        end else begin
            // Log unauthorized access attempt
            \$display("Unauthorized access attempt detected at address: %d", addr);
            data_out <= 8'b00000000;  // Return a default value on unauthorized access attempt
        end
    end
endmodule

In this fixed example, the access control check is performed before any memory read or write operation, ensuring that unauthorized users are prevented from accessing or modifying the memory content. Unauthorized access attempts are logged, and a default value is returned to avoid exposing sensitive data.