Improper Protection for Outbound Error Messages and Alert Signals

Description

Improper Protection for Outbound Error Messages and Alert Signals occurs when untrusted agents can disable alerts about signal conditions exceeding limits or the response mechanism that handles such alerts. Hardware devices rely on sensors to detect out-of-bounds operating conditions and trigger alert signals that prompt remedial actions like shutdown or throttling. When these protective alerts lack proper security controls, malicious software can mask or disable them, particularly affecting thermal and power management systems.

Risk

Improper alert protection has severe implications. Thermal alerts disabled causing overheating. Power alerts masked allowing damage. Protective shutdowns prevented. Hardware damage possible. Denial of service through induced failures. System instability. Safety mechanisms defeated. Component lifetime reduced. Physical damage to devices. High likelihood when alert configurations are accessible to untrusted software.

Solution

Alert signals generated by critical events should be protected from access by untrusted agents during architecture and design phase. Only hardware or trusted firmware modules should be able to alter the alert configuration. Implement access control on GPIO and interrupt configuration registers. Lock alert thresholds after secure initialization. Use hardware enforcement of alert responses that cannot be overridden by software.

Common Consequences

Impact	Details
Availability	Scope: Availability System instability, crashes, and denial-of-service through disabled protective alerts.
Integrity	Scope: Integrity Safety mechanisms compromised allowing operation outside safe parameters.

Example Code

Vulnerable Code

// Vulnerable: Thermal alert controller without access protection

module vulnerable_thermal_alert (
    input  wire        clk,
    input  wire        rst_n,

    // Temperature sensor interface
    input  wire [11:0] temperature,     // Current temperature (ADC value)

    // Alert configuration (VULNERABLE: no protection)
    input  wire        config_write_en,
    input  wire [11:0] config_threshold,
    input  wire        config_alert_enable,
    input  wire [1:0]  config_gpio_mask,

    // Alert outputs
    output reg         alert_out,
    output reg         shutdown_request,
    output reg  [1:0]  gpio_alert
);

    // Configuration registers
    reg [11:0] threshold_reg;
    reg        alert_enabled;
    reg [1:0]  gpio_mask;

    // VULNERABLE: Any software can modify alert configuration
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            threshold_reg <= 12'hFFF;  // Max threshold - no alert
            alert_enabled <= 1'b1;
            gpio_mask <= 2'b11;
        end else if (config_write_en) begin
            // VULNERABLE: No access control
            threshold_reg <= config_threshold;
            alert_enabled <= config_alert_enable;
            gpio_mask <= config_gpio_mask;
        end
    end

    // Temperature comparison and alert generation
    wire over_temp = (temperature > threshold_reg);

    always @(posedge clk) begin
        // VULNERABLE: Alert can be disabled by untrusted software
        if (over_temp && alert_enabled) begin
            alert_out <= 1'b1;
            shutdown_request <= 1'b1;
            gpio_alert <= gpio_mask;
        end else begin
            alert_out <= 1'b0;
            shutdown_request <= 1'b0;
            gpio_alert <= 2'b00;
        end
    end

    // Attack scenarios:
    // 1. Set threshold_reg = 0xFFF (max) - never triggers
    // 2. Set alert_enabled = 0 - alerts disabled
    // 3. Set gpio_mask = 0 - GPIO signals blocked
    // Result: Device overheats without triggering protection

endmodule

// Vulnerable: Power management with unprotected alerts
module vulnerable_power_alert (
    input  wire        clk,
    input  wire        rst_n,

    // Power sensor
    input  wire [15:0] power_reading,

    // Alert configuration
    input  wire        cfg_write,
    input  wire [15:0] cfg_power_limit,
    input  wire        cfg_alert_enable,
    input  wire        cfg_throttle_enable,

    // Alert and response
    output reg         power_alert,
    output reg         throttle_request
);

    reg [15:0] power_limit;
    reg        alert_en;
    reg        throttle_en;

    // VULNERABLE: Configuration accessible to all software
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            power_limit <= 16'd1000;
            alert_en <= 1'b1;
            throttle_en <= 1'b1;
        end else if (cfg_write) begin
            // VULNERABLE: Untrusted software can disable protection
            power_limit <= cfg_power_limit;
            alert_en <= cfg_alert_enable;
            throttle_en <= cfg_throttle_enable;
        end
    end

    wire over_power = (power_reading > power_limit);

    // VULNERABLE: Alerts and throttling can be masked
    always @(posedge clk) begin
        power_alert <= over_power && alert_en;
        throttle_request <= over_power && throttle_en;
    end

    // Attack: Disable throttle_en, run at max power
    // Result: Component damage, reduced lifetime

endmodule

// Vulnerable: Software thermal management without protection

#include <stdint.h>
#include <stdbool.h>

// GPIO registers for thermal alerts
#define GPIO_THERMAL_OUT    (*((volatile uint32_t*)0x40000100))
#define GPIO_THERMAL_EN     (*((volatile uint32_t*)0x40000104))
#define GPIO_THERMAL_CFG    (*((volatile uint32_t*)0x40000108))

// VULNERABLE: Global configuration accessible to all
static struct {
    uint16_t threshold;
    bool alert_enabled;
    bool gpio_enabled;
} thermal_config = {
    .threshold = 85,  // 85°C
    .alert_enabled = true,
    .gpio_enabled = true
};

// VULNERABLE: Any code can modify configuration
void vulnerable_set_thermal_threshold(uint16_t threshold) {
    thermal_config.threshold = threshold;
}

void vulnerable_disable_thermal_alert(void) {
    thermal_config.alert_enabled = false;
    GPIO_THERMAL_EN = 0;  // Disable GPIO output
}

void vulnerable_mask_gpio_alert(void) {
    thermal_config.gpio_enabled = false;
    GPIO_THERMAL_CFG = 0;  // Mask GPIO signal
}

// Attack code example:
void malicious_disable_protection(void) {
    // Disable all thermal protection
    vulnerable_set_thermal_threshold(0xFFFF);  // Never triggers
    vulnerable_disable_thermal_alert();
    vulnerable_mask_gpio_alert();

    // Now run intensive workload without thermal protection
    // Device overheats and may be damaged
}

Fixed Code

// Fixed: Thermal alert controller with access protection

module secure_thermal_alert (
    input  wire        clk,
    input  wire        rst_n,

    // Temperature sensor interface
    input  wire [11:0] temperature,

    // Alert configuration (protected)
    input  wire        config_write_en,
    input  wire [11:0] config_threshold,
    input  wire        config_alert_enable,
    input  wire [1:0]  config_gpio_mask,
    input  wire        privileged_access,    // FIXED: Privilege signal
    input  wire        boot_complete,        // FIXED: Lifecycle signal

    // Alert outputs
    output reg         alert_out,
    output reg         shutdown_request,
    output reg  [1:0]  gpio_alert,
    output reg         config_denied,
    output reg         config_locked
);

    // Configuration registers
    reg [11:0] threshold_reg;
    reg        alert_enabled;
    reg [1:0]  gpio_mask;

    // FIXED: Safe parameter ranges
    localparam MIN_THRESHOLD = 12'h100;  // Minimum threshold value
    localparam MAX_THRESHOLD = 12'hC00;  // Maximum safe threshold

    // FIXED: Lock configuration after boot
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            config_locked <= 1'b0;
        end else if (boot_complete) begin
            config_locked <= 1'b1;
        end
    end

    // FIXED: Protected configuration with access control
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            threshold_reg <= 12'h800;  // Safe default threshold
            alert_enabled <= 1'b1;     // FIXED: Always enabled by default
            gpio_mask <= 2'b11;
            config_denied <= 1'b0;
        end else if (config_write_en) begin
            config_denied <= 1'b0;

            // FIXED: Check privilege and lock status
            if (!privileged_access || config_locked) begin
                config_denied <= 1'b1;
            end else begin
                // FIXED: Validate threshold range
                if (config_threshold >= MIN_THRESHOLD &&
                    config_threshold <= MAX_THRESHOLD) begin
                    threshold_reg <= config_threshold;
                end else begin
                    config_denied <= 1'b1;
                end

                // FIXED: Alert cannot be disabled
                // alert_enabled always stays true
                if (!config_alert_enable) begin
                    config_denied <= 1'b1;  // Deny disable request
                end

                // FIXED: GPIO mask can only enable more signals
                if (config_gpio_mask != 2'b00) begin
                    gpio_mask <= gpio_mask | config_gpio_mask;
                end
            end
        end
    end

    // Temperature comparison
    wire over_temp = (temperature > threshold_reg);

    // FIXED: Hardware-enforced alert that cannot be disabled
    always @(posedge clk) begin
        // FIXED: Alert always active when over temperature
        // No software can disable this
        alert_out <= over_temp;
        shutdown_request <= over_temp;
        gpio_alert <= over_temp ? gpio_mask : 2'b00;
    end

endmodule

// Fixed: Power alert with hardware enforcement
module secure_power_alert (
    input  wire        clk,
    input  wire        rst_n,

    // Power sensor
    input  wire [15:0] power_reading,

    // Protected configuration
    input  wire        cfg_write,
    input  wire [15:0] cfg_power_limit,
    input  wire        cfg_alert_enable,
    input  wire        cfg_throttle_enable,
    input  wire        trusted_access,       // FIXED: Access control
    input  wire        config_lock,          // FIXED: Lock signal

    // Alert and response
    output reg         power_alert,
    output reg         throttle_request,
    output reg         cfg_denied
);

    reg [15:0] power_limit;
    reg config_locked;

    // FIXED: Hardware-enforced minimum/maximum limits
    localparam MIN_POWER_LIMIT = 16'd100;
    localparam MAX_POWER_LIMIT = 16'd2000;
    localparam ABSOLUTE_LIMIT = 16'd2500;  // Hardware enforced

    // FIXED: Lock after configuration
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            config_locked <= 1'b0;
        end else if (config_lock) begin
            config_locked <= 1'b1;
        end
    end

    // FIXED: Protected configuration
    always @(posedge clk or negedge rst_n) begin
        if (!rst_n) begin
            power_limit <= 16'd1000;
            cfg_denied <= 1'b0;
        end else if (cfg_write) begin
            cfg_denied <= 1'b0;

            if (!trusted_access || config_locked) begin
                cfg_denied <= 1'b1;
            end else if (cfg_power_limit < MIN_POWER_LIMIT ||
                        cfg_power_limit > MAX_POWER_LIMIT) begin
                cfg_denied <= 1'b1;
            end else begin
                power_limit <= cfg_power_limit;
            end

            // FIXED: Cannot disable alert or throttle
            if (!cfg_alert_enable || !cfg_throttle_enable) begin
                cfg_denied <= 1'b1;
            end
        end
    end

    // FIXED: Hardware-enforced alerts
    wire over_config_limit = (power_reading > power_limit);
    wire over_absolute_limit = (power_reading > ABSOLUTE_LIMIT);

    always @(posedge clk) begin
        // FIXED: Alert always active - cannot be disabled
        power_alert <= over_config_limit;

        // FIXED: Hardware-enforced absolute limit
        // Even if config limit is set high, this triggers
        throttle_request <= over_config_limit || over_absolute_limit;
    end

endmodule

// Fixed: Software thermal management with protection

#include <stdint.h>
#include <stdbool.h>

// GPIO registers (same addresses but protected by hardware)
#define GPIO_THERMAL_OUT    (*((volatile uint32_t*)0x40000100))
#define GPIO_THERMAL_EN     (*((volatile uint32_t*)0x40000104))
#define GPIO_THERMAL_CFG    (*((volatile uint32_t*)0x40000108))
#define GPIO_THERMAL_LOCK   (*((volatile uint32_t*)0x4000010C))

// FIXED: Configuration with access control
typedef struct {
    uint16_t threshold;
    bool locked;
} secure_thermal_config_t;

static secure_thermal_config_t thermal_config = {
    .threshold = 85,
    .locked = false
};

// FIXED: Safe threshold bounds
#define MIN_THRESHOLD 40
#define MAX_THRESHOLD 100

// FIXED: Secure configuration with privilege check
bool secure_set_thermal_threshold(uint16_t threshold, bool privileged) {
    // FIXED: Check privilege
    if (!privileged) {
        return false;
    }

    // FIXED: Check lock
    if (thermal_config.locked) {
        return false;
    }

    // FIXED: Validate range
    if (threshold < MIN_THRESHOLD || threshold > MAX_THRESHOLD) {
        return false;
    }

    thermal_config.threshold = threshold;
    return true;
}

// FIXED: Lock configuration - cannot be undone
void secure_lock_thermal_config(void) {
    thermal_config.locked = true;
    GPIO_THERMAL_LOCK = 1;  // Hardware lock
}

// FIXED: Alert cannot be disabled
// No function to disable thermal alert - it's always enabled

// FIXED: Initialization function (called during secure boot)
void secure_thermal_init(void) {
    // Set safe default threshold
    thermal_config.threshold = 85;

    // Enable all alert outputs
    GPIO_THERMAL_EN = 0xFFFFFFFF;
    GPIO_THERMAL_CFG = 0xFFFFFFFF;

    // FIXED: Lock configuration
    secure_lock_thermal_config();

    // After this, no software can modify thermal alerts
}

CVE Examples

CVE-2020-8693: Improper access control for thermal alerts in Intel processors allowed denial of service.
CVE-2019-11137: Insufficient access control on power management interfaces.

CWE-284: Improper Access Control (parent)
CWE-1206: Power, Clock, Thermal, and Reset Concerns (category)
CWE-1314: Missing Write Protection for Parametric Data Values (related)
CAPEC-1: Accessing Functionality Not Properly Constrained by ACLs
CAPEC-180: Exploiting Incorrectly Configured Access Control Security Levels

References

MITRE Corporation. "CWE-1320: Improper Protection for Outbound Error Messages and Alert Signals." https://cwe.mitre.org/data/definitions/1320.html
Intel. "Thermal Management Guidelines"
JEDEC. "Power Management Standards"

Improper Protection for Outbound Error Messages and Alert Signals

Description

Risk

Solution

Common Consequences

Example Code

Vulnerable Code

Fixed Code

CVE Examples

References

Cyber Security Consulting

Industries

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Improper Protection for Outbound Error Messages and Alert Signals

Description

Risk

Solution

Common Consequences

Example Code

Vulnerable Code

Fixed Code

CVE Examples

Related CWEs

References