Internal Asset Exposed to Unsafe Debug Access Level or State

Description

Internal Asset Exposed to Unsafe Debug Access Level or State occurs when a product uses physical debug or test interfaces with multiple access levels but assigns incorrect debug access to internal assets, providing unintended access from untrusted debug agents. Debug authorization supports multiple access levels controlling which system assets are accessible based on authenticated privilege. Authorization can depend on system state or boot stage. For instance, full system debug access might only be allowed early in boot after a system reset to ensure that previous session data is not accessible.

Risk

Incorrect debug access levels have severe security implications. Sensitive assets may be accessible at wrong privilege levels. Debug access during wrong boot stages may expose secrets. Attackers may modify boot flow through debug. Encryption keys may be accessible before lockdown. Memory protection may be bypassable through debug. Previous session data may be accessible. Privilege escalation may be possible through debug.

Solution

Ensure debug access levels correctly protect all internal assets. Restrict full debug access to appropriate boot stages. Default debug protection registers to secured state. Use AND logic rather than OR for combining access checks. Verify debug protection across all system states. Test debug access at each boot stage. Document debug access requirements for each asset. Implement proper debug authentication.

Common Consequences

Impact	Details
Confidentiality	Scope: Confidentiality Read Memory - Attackers could obtain sensitive information from internal assets using a debugger if protection mechanisms fail to enforce correct debug access levels.
Integrity	Scope: Integrity Modify Memory - Unauthorized memory alteration through improperly protected debug access.
Access Control	Scope: Access Control Bypass Protection Mechanism, Gain Privileges - Authorization and access control violations enabling unauthorized privilege assumption.

Example Code

Vulnerable Code

// Vulnerable: JTAG access allowed before security initialization

module vulnerable_jtag_protection (
    input wire clk,
    input wire reset_n,
    input wire jtag_request,
    input wire [31:0] jtag_addr,
    input wire jtag_write,
    input wire [31:0] jtag_wdata,
    input wire boot_complete,
    input wire security_init_done,
    output reg [31:0] jtag_rdata,
    output reg jtag_ack
);

    // JTAG shield register
    reg jtag_shield_enabled;

    always @(posedge clk or negedge reset_n) begin
        if (!reset_n) begin
            // VULNERABLE: JTAG protection disabled by default!
            jtag_shield_enabled <= 1'b0;  // Should be 1'b1
        end
        else if (boot_complete) begin
            // Shield only enabled after boot completes
            // Too late - attacker can access during boot
            jtag_shield_enabled <= 1'b1;
        end
    end

    // VULNERABLE: Full JTAG access before boot_complete
    always @(posedge clk) begin
        if (jtag_request) begin
            if (!jtag_shield_enabled) begin
                // JTAG has full access during early boot!
                if (jtag_write) begin
                    memory[jtag_addr] <= jtag_wdata;  // Can modify boot code!
                end else begin
                    jtag_rdata <= memory[jtag_addr];  // Can read keys!
                end
                jtag_ack <= 1'b1;
            end else begin
                jtag_ack <= 1'b0;  // Blocked after boot
            end
        end
    end

    // Attack window: From reset to boot_complete, full debug access

endmodule

// Vulnerable: Debug privilege check uses OR instead of AND
module vulnerable_debug_auth (
    input wire clk,
    input wire reset_n,
    input wire debug_request,
    input wire debug_mode_active,
    input wire user_mode,
    input wire password_correct,
    output reg debug_allowed
);

    // VULNERABLE: OR logic - either condition allows access
    always @(posedge clk or negedge reset_n) begin
        if (!reset_n) begin
            debug_allowed <= 1'b0;
        end
        else begin
            // Bug: debug_mode_active OR user_mode grants access
            // Should require BOTH conditions
            debug_allowed <= debug_request && (debug_mode_active || password_correct);
        end
    end

    // If debug_mode_active is set (e.g., by pulling a pin), no password needed

endmodule

// Vulnerable: Debug access level not matched to boot stage
module vulnerable_boot_debug (
    input wire clk,
    input wire reset_n,
    input wire [2:0] boot_stage,
    input wire debug_request,
    input wire [2:0] debug_access_level,
    input wire [31:0] debug_addr,
    output reg [31:0] debug_data,
    output reg debug_granted
);

    // Boot stages
    parameter STAGE_ROM = 3'h0;
    parameter STAGE_BOOTLOADER = 3'h1;
    parameter STAGE_KERNEL = 3'h2;
    parameter STAGE_USER = 3'h3;

    // Debug access levels
    parameter ACCESS_NONE = 3'h0;
    parameter ACCESS_USER = 3'h1;
    parameter ACCESS_PRIVILEGED = 3'h2;
    parameter ACCESS_FULL = 3'h3;

    always @(posedge clk) begin
        if (debug_request) begin
            // VULNERABLE: Access level not properly restricted by boot stage
            // Full access allowed even in later boot stages
            if (debug_access_level == ACCESS_FULL) begin
                debug_data <= memory[debug_addr];
                debug_granted <= 1'b1;
            end
            else begin
                debug_granted <= 1'b0;
            end
        end
    end

    // Should restrict full access to early boot only

endmodule

// Vulnerable: Debug access during sensitive boot operations

void vulnerable_secure_boot(void) {
    // Load encryption keys
    load_boot_keys();  // Keys now in memory

    // VULNERABLE: Debug still enabled, keys accessible!

    // Verify firmware signature
    if (!verify_signature()) {
        // Boot failed, but debug can still access keys
        halt();
    }

    // Eventually disable debug...
    disable_debug();  // Too late - keys may have been extracted
}

// Vulnerable: Debug privilege check
bool vulnerable_debug_check(uint32_t addr) {
    // VULNERABLE: Always allow debug during boot
    if (!boot_complete) {
        return true;  // Full access during boot
    }

    // After boot, check privilege
    return is_privileged_debug();
}

Fixed Code

// Fixed: JTAG protection enabled by default

module secure_jtag_protection (
    input wire clk,
    input wire reset_n,
    input wire jtag_request,
    input wire [31:0] jtag_addr,
    input wire jtag_write,
    input wire [31:0] jtag_wdata,
    input wire jtag_authenticated,  // Requires authentication
    input wire boot_complete,
    input wire security_init_done,
    output reg [31:0] jtag_rdata,
    output reg jtag_ack,
    output reg jtag_denied
);

    // JTAG shield register
    reg jtag_shield_enabled;

    always @(posedge clk or negedge reset_n) begin
        if (!reset_n) begin
            // FIXED: JTAG protection ENABLED by default
            jtag_shield_enabled <= 1'b1;
        end
        // Shield can only be disabled with authentication after security init
        else if (security_init_done && jtag_authenticated) begin
            // Allow authenticated debug after security is configured
            jtag_shield_enabled <= 1'b0;
        end
    end

    // FIXED: JTAG blocked until authenticated
    always @(posedge clk) begin
        jtag_denied <= 1'b0;

        if (jtag_request) begin
            if (jtag_shield_enabled) begin
                // Debug blocked
                jtag_rdata <= 32'h0;
                jtag_ack <= 1'b0;
                jtag_denied <= 1'b1;
            end
            else if (jtag_authenticated) begin
                // Authenticated debug allowed
                if (jtag_write) begin
                    memory[jtag_addr] <= jtag_wdata;
                end else begin
                    jtag_rdata <= memory[jtag_addr];
                end
                jtag_ack <= 1'b1;
            end
            else begin
                jtag_ack <= 1'b0;
                jtag_denied <= 1'b1;
            end
        end
    end

endmodule

// Fixed: Debug privilege check uses AND logic
module secure_debug_auth (
    input wire clk,
    input wire reset_n,
    input wire debug_request,
    input wire debug_mode_active,
    input wire user_authorized,
    input wire password_correct,
    output reg debug_allowed
);

    always @(posedge clk or negedge reset_n) begin
        if (!reset_n) begin
            debug_allowed <= 1'b0;
        end
        else begin
            // FIXED: AND logic - ALL conditions required
            debug_allowed <= debug_request &&
                            debug_mode_active &&
                            user_authorized &&
                            password_correct;
        end
    end

endmodule

// Fixed: Debug access level matched to boot stage
module secure_boot_debug (
    input wire clk,
    input wire reset_n,
    input wire [2:0] boot_stage,
    input wire debug_request,
    input wire [2:0] debug_access_level,
    input wire debug_authenticated,
    input wire [31:0] debug_addr,
    output reg [31:0] debug_data,
    output reg debug_granted,
    output reg access_violation
);

    // Boot stages
    parameter STAGE_ROM = 3'h0;
    parameter STAGE_BOOTLOADER = 3'h1;
    parameter STAGE_KERNEL = 3'h2;
    parameter STAGE_USER = 3'h3;

    // Debug access levels
    parameter ACCESS_NONE = 3'h0;
    parameter ACCESS_USER = 3'h1;
    parameter ACCESS_PRIVILEGED = 3'h2;
    parameter ACCESS_FULL = 3'h3;

    // Maximum allowed access level per boot stage
    function [2:0] max_access_for_stage;
        input [2:0] stage;
        begin
            case (stage)
                STAGE_ROM: max_access_for_stage = ACCESS_NONE;      // No debug during ROM
                STAGE_BOOTLOADER: max_access_for_stage = ACCESS_PRIVILEGED;  // Limited
                STAGE_KERNEL: max_access_for_stage = ACCESS_PRIVILEGED;
                STAGE_USER: max_access_for_stage = ACCESS_USER;     // User-level only
                default: max_access_for_stage = ACCESS_NONE;
            endcase
        end
    endfunction

    always @(posedge clk) begin
        access_violation <= 1'b0;

        if (debug_request && debug_authenticated) begin
            // FIXED: Check access level is appropriate for boot stage
            if (debug_access_level <= max_access_for_stage(boot_stage)) begin
                debug_data <= memory[debug_addr];
                debug_granted <= 1'b1;
            end
            else begin
                // Access level too high for current boot stage
                debug_data <= 32'h0;
                debug_granted <= 1'b0;
                access_violation <= 1'b1;
            end
        end
        else begin
            debug_granted <= 1'b0;
        end
    end

endmodule

// Fixed: Debug properly restricted during secure boot

void secure_boot_sequence(void) {
    // FIXED: Disable debug BEFORE loading keys
    disable_debug_access();

    // Verify debug is disabled
    if (is_debug_enabled()) {
        panic("Debug not disabled during secure boot!");
    }

    // Now safe to load keys
    load_boot_keys();

    // Verify firmware signature
    if (!verify_signature()) {
        // Clear keys before halting
        clear_boot_keys();
        halt();
    }

    // Clear keys from memory after use
    clear_boot_keys();

    // Debug can be re-enabled after boot if needed
    // (with proper authentication)
}

// Fixed: Debug privilege properly checked
bool secure_debug_check(uint32_t addr, uint32_t access_level) {
    uint32_t current_stage = get_boot_stage();
    uint32_t max_level = get_max_debug_level(current_stage);

    // Check authentication
    if (!is_debug_authenticated()) {
        return false;
    }

    // Check access level appropriate for boot stage
    if (access_level > max_level) {
        log_security_event("Debug access level violation: %d > %d",
                          access_level, max_level);
        return false;
    }

    // Check address is accessible at this level
    if (!is_address_accessible(addr, access_level)) {
        return false;
    }

    return true;
}

uint32_t get_max_debug_level(uint32_t boot_stage) {
    switch (boot_stage) {
        case STAGE_ROM:
            return ACCESS_NONE;        // No debug during ROM
        case STAGE_BOOTLOADER:
            return ACCESS_PRIVILEGED;  // Limited access
        case STAGE_KERNEL:
            return ACCESS_PRIVILEGED;
        case STAGE_USER:
            return ACCESS_USER;        // User-level only
        default:
            return ACCESS_NONE;
    }
}

CVE Examples

CVE-2019-18827: JTAG access possible before ROM code execution on Barco ClickShare
CVA6 processor debug mode vulnerabilities

CWE-863: Incorrect Authorization (parent)
CWE-1191: On-Chip Debug and Test Interface With Improper Access Control (related)
CWE-1243: Sensitive Non-Volatile Information Not Protected During Debug (related)

References

MITRE Corporation. "CWE-1244: Internal Asset Exposed to Unsafe Debug Access Level or State." https://cwe.mitre.org/data/definitions/1244.html
REF-1377, REF-1378: CVA6 Processor Vulnerability Examples
REF-1056: Barco ClickShare JTAG Vulnerabilities

Internal Asset Exposed to Unsafe Debug Access Level or State

Description

Risk

Solution

Common Consequences

Example Code

Vulnerable Code

Fixed Code

CVE Examples

References

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Internal Asset Exposed to Unsafe Debug Access Level or State

Description

Risk

Solution

Common Consequences

Example Code

Vulnerable Code

Fixed Code

CVE Examples

Related CWEs

References