CVE-2025-7432

Executive Summary

CVE-2025-7432 identifies a critical flaw in the Differential Power Analysis (DPA) countermeasures implemented in Silicon Labs' Series 2 devices. Under specific, undisclosed conditions, the random number generator used for cryptographic operations is not reseeded. This allows an attacker with physical access to the device to perform a DPA attack, eventually extracting secret cryptographic keys. The vulnerability is currently unpatched, and no public proof-of-concept (PoC) or exploit code is available. The impact is severe for any application relying on the confidentiality of keys stored or used by these devices, including IoT, industrial control, and secure communication systems.

Supply Chain & Package Security

This vulnerability is not related to software packages (NPM, PyPI, Go, Ruby) but is a hardware-level cryptographic implementation flaw. The supply chain risk lies in the physical devices themselves. Organizations using Silicon Labs Series 2 microcontrollers must assess their inventory and consider the physical security of deployed devices until a firmware patch is released.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that a full vector has not been assigned by NVD. However, based on the nature of the vulnerability, a realistic assessment would be:

• Attack Vector (AV): Physical (requires physical access to the device)
• Attack Complexity (AC): High (requires specialized equipment and expertise for DPA)
• Privileges Required (PR): None
• User Interaction (UI): None
• Scope (S): Changed (compromise of keys affects the entire system)
• Confidentiality (C): High (secret keys are extracted)
• Integrity (I): High (keys can be used to forge or decrypt data)
• Availability (A): None

Estimated CVSS Vector: CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N
Estimated Score: 6.6 (Medium)

Threat Level: High for environments where physical security is weak or devices are deployed in untrusted locations.

Deep Dive & Mechanics

DPA is a side-channel attack that analyzes the power consumption of a cryptographic device during operations. By statistically correlating power traces with known data, an attacker can deduce secret keys. To mitigate this, hardware designers implement countermeasures such as randomizing the order of operations, adding noise, or using random masks.

The vulnerability in CVE-2025-7432 lies in the reseeding mechanism of the DPA countermeasure's random number generator. Under certain conditions (e.g., specific power states, temperature ranges, or after a certain number of operations), the generator fails to reseed. This means the same random values are reused across multiple cryptographic operations, making the power traces statistically correlated and vulnerable to DPA.

Attack Flow:

1. Attacker gains physical access to the target device.
2. Attacker triggers the vulnerable condition (e.g., by cycling power or sending specific commands).
3. Attacker captures power traces while the device performs cryptographic operations (e.g., AES encryption).
4. Using statistical analysis (e.g., correlation power analysis), the attacker extracts the secret key.

Vulnerable vs. Patched Code

No code is available for this vulnerability. The flaw is in the hardware/firmware of Silicon Labs Series 2 devices. A patched version would ensure that the random number generator is reseeded before each cryptographic operation or at regular intervals, breaking the statistical correlation.

Vulnerable Behavior:

• Random number generator state is not refreshed.
• Same mask or random value used for multiple operations.

Patched Behavior:

• Random number generator is reseeded from a true random source before each operation.
• DPA countermeasures are re-initialized on every cryptographic call.

Exploitation & Lab Setup

No public exploit code is available. The following is a theoretical lab setup for testing.

Red Team (Offensive)

Objective: Extract an AES-128 key from a Silicon Labs Series 2 device.

Equipment:

• Silicon Labs Series 2 development board (e.g., EFR32MG24)
• Oscilloscope (e.g., PicoScope 6404D) with high sampling rate (1 GS/s)
• Current probe (e.g., Tektronix TCP0030A) or shunt resistor
• Computer with Python and ChipWhisperer or similar DPA toolkit

Steps:

1. Setup: Connect the current probe to the device's power supply. Connect the oscilloscope to the probe.
2. Trigger: Configure the device to perform AES encryption on a known plaintext. Use a GPIO pin as a trigger for the oscilloscope.
3. Capture: Write a script to send the plaintext, capture the power trace, and save it.
4. Repeat: Capture thousands of traces with the same key but different plaintexts.
5. Analyze: Use a DPA tool (e.g., ChipWhisperer's dpa module) to correlate power traces with hypothetical intermediate values. The key byte that produces the highest correlation is the correct one.

Example Python snippet (conceptual):

import chipwhisperer as cw
scope = cw.scope()
target = cw.target(scope)
scope.default_setup()
# Capture traces
traces = []
for i in range(10000):
    target.simpleserial_write('p', plaintext)
    scope.arm()
    target.simpleserial_go()
    traces.append(scope.capture())
# Perform DPA
key = cw.dpa(traces, plaintexts, target)
print("Extracted key:", key)

Blue Team (Defensive)

Objective: Detect and mitigate DPA attacks on Silicon Labs Series 2 devices.

Detection:

• Monitor for unusual power consumption patterns (requires hardware monitoring).
• Implement physical security measures (tamper switches, enclosures).
• Use anomaly detection on the device's power rail (e.g., detect sudden high-frequency noise).

Mitigation:

• Apply firmware patches as soon as they are released by Silicon Labs.
• If patching is not possible, limit physical access to devices.
• Use additional cryptographic layers (e.g., key wrapping) to reduce the impact of key extraction.
• Implement rate limiting on cryptographic operations to increase the time needed for DPA.

Indicators of Compromise (IOCs)

No software-based IOCs exist. The following are physical and behavioral indicators:

• Physical: Unusual probes or wires attached to the device's power pins.
• Behavioral: Device performing cryptographic operations at unexpected times or with unusual frequency.
• Power Analysis: High-frequency noise on the power rail during cryptographic operations (indicating active DPA capture).

Detection Engineering

YARA Rule

rule CVE_2025_7432_DPA_Vulnerability {
    meta:
        description = "Detects firmware images with known DPA countermeasure flaw in Silicon Labs Series 2"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-7432"
    strings:
        $dpa_weak = { 48 65 6C 6C 6F }  // Placeholder for a unique byte sequence in vulnerable firmware
    condition:
        $dpa_weak
}

Sigma Rule

title: DPA Countermeasure Failure in Silicon Labs Series 2
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects potential exploitation of CVE-2025-7432 via power analysis
author: Valters IT
logsource:
    product: hardware
    service: power_monitor
detection:
    selection:
        power_noise_frequency: "high"
        crypto_operation_count: ">1000"
    condition: selection
falsepositives:
    - Normal cryptographic operations
level: high

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-7432 DPA Attack Detection"; flow:to_server; content:"|00 01 02 03|"; depth:4; sid:1000001; rev:1;)

Note: Suricata rules are not effective for hardware-level attacks. This is a placeholder for network-based detection of related command-and-control traffic.

Remediation & Mitigation

Immediate Actions:

1. Isolate Devices: If possible, disconnect affected devices from sensitive networks until a patch is available.
2. Physical Security: Ensure devices are in tamper-proof enclosures with monitoring.
3. Monitor: Watch for Silicon Labs security advisories for a firmware update.

Long-Term Fix:

• Apply the official firmware patch from Silicon Labs once released.
• If no patch is forthcoming, consider replacing Series 2 devices with Series 3 or other hardware with verified DPA countermeasures.

Workaround:

• Implement a software-based key derivation function that uses a hardware true random number generator (TRNG) to derive session keys, reducing the value of the static key.

Valters IT