CVE-2025-14859

Executive Summary

CVE-2025-14859 identifies a critical cryptographic weakness in the secure boot implementation of Semtech LR11xx LoRa transceivers. The vulnerability stems from the use of a non-standard, weak hashing algorithm that is susceptible to second preimage attacks. An attacker with physical access to the device can craft a malicious firmware image that produces the same hash as a legitimate signed image, thereby bypassing the digital signature verification process. This allows the installation of arbitrary, unauthorized firmware, effectively compromising the device's integrity and trust model. The vulnerability has a CVSS score of 0.0 (likely uncalculated or placeholder), but based on the vector, it represents a high-severity physical attack vector with significant confidentiality, integrity, and availability impact. No public exploit code or patch is currently available.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a hardware/firmware-level issue in Semtech's LoRa transceiver chips. The supply chain risk is primarily for IoT device manufacturers who integrate these chips into their products, as they may unknowingly ship devices with a broken secure boot mechanism.

CVSS Breakdown & Threat Level

CVSS Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Threat Level: Critical (Physical access required, but impact is total compromise of the device's security model).

Deep Dive & Mechanics

The Semtech LR11xx series implements a secure boot chain to ensure only cryptographically signed firmware can be executed. This process typically involves:

1. Boot ROM: Immutable code that runs on power-up.
2. Signature Verification: The boot ROM reads the firmware image and its attached digital signature.
3. Hash Calculation: A cryptographic hash of the firmware image is calculated.
4. Signature Check: The hash is verified against the digital signature using a public key embedded in the device.

The Vulnerability: The flaw lies in step 3. Instead of using a standard, collision-resistant hash function (like SHA-256), Semtech implemented a non-standard cryptographic hashing algorithm. This custom algorithm is vulnerable to a second preimage attack.

• Second Preimage Attack: Given a message M1 and its hash H(M1), an attacker can find a different message M2 such that H(M2) = H(M1).
• Exploitation: An attacker obtains a legitimate signed firmware image (e.g., from a public update server or by extracting it from a device). They then analyze the weak hash function and craft a malicious firmware image that produces the exact same hash value. The digital signature from the legitimate image is still valid for this new hash, so the secure boot verification passes, and the malicious firmware is executed.

This bypasses the entire trust anchor of the device, allowing an attacker to install persistent malware, modify device behavior, or exfiltrate sensitive data.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the conceptual difference is:

Vulnerable Implementation (Conceptual Pseudocode):

// Non-standard, weak hash function
uint32_t weak_hash(uint8_t *data, size_t len) {
    uint32_t hash = 0;
    for (size_t i = 0; i < len; i++) {
        hash = (hash * 31) + data[i]; // Simple, invertible operation
    }
    return hash;
}

bool verify_firmware(uint8_t *firmware, size_t len, uint8_t *signature) {
    uint32_t hash = weak_hash(firmware, len);
    // Verify signature against the weak hash
    return rsa_verify(hash, signature, public_key);
}

Patched Implementation (Conceptual Pseudocode):

// Standard, collision-resistant hash function
bool verify_firmware(uint8_t *firmware, size_t len, uint8_t *signature) {
    uint8_t hash[SHA256_DIGEST_LENGTH];
    sha256(firmware, len, hash); // Use SHA-256
    // Verify signature against the strong hash
    return rsa_verify(hash, signature, public_key);
}

The fix involves replacing the custom weak hash with a standard cryptographic hash like SHA-256 or SHA-3.

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Physical access to a device with a Semtech LR11xx transceiver.
• A legitimate signed firmware image for the target device.
• Tools: Logic analyzer, JTAG/SWD debugger, custom firmware patching tools, Python with hashlib (for analysis).

Attack Steps:

1. Extract Legitimate Firmware: Use a logic analyzer or JTAG to dump the firmware from the device's flash memory during a legitimate update process.
2. Reverse Engineer Hash Function: Analyze the boot ROM code (extracted via JTAG) to identify the custom hash algorithm. This may involve static analysis of the ARM/Thumb assembly.
3. Develop Collision Generator: Write a script (e.g., in Python) that, given the legitimate firmware and its hash, finds a second preimage (malicious firmware) that produces the same hash. This is algorithm-specific but may involve brute-forcing padding or exploiting algebraic weaknesses.
4. Craft Malicious Firmware: Create a malicious firmware image that includes your payload (e.g., backdoor, data exfiltration) and has the same hash as the legitimate image.
5. Flash Malicious Firmware: Use the device's update mechanism (e.g., UART, SPI) to flash the malicious firmware. The secure boot will accept it.

Example Collision Generation (Conceptual Python):

# This is a simplified example for a hypothetical weak hash.
# Real exploitation requires reversing the actual custom algorithm.
def weak_hash(data):
    h = 0
    for byte in data:
        h = (h * 31 + byte) & 0xFFFFFFFF
    return h

def find_collision(legitimate_firmware, malicious_payload):
    legit_hash = weak_hash(legitimate_firmware)
    # Brute-force padding to match hash (simplified)
    for pad in range(1000000):
        test_firmware = malicious_payload + pad.to_bytes(4, 'little')
        if weak_hash(test_firmware) == legit_hash:
            return test_firmware
    return None

Blue Team (Defense & Detection)

Defensive Measures:

• Physical Security: Restrict physical access to devices. Use tamper-evident seals and enclosures.
• Secure Boot Logging: Enable and monitor secure boot status registers (if available) for failures.
• Firmware Integrity Monitoring: Implement runtime integrity checks (e.g., IMA - Integrity Measurement Architecture) to detect unauthorized code execution.
• Network Segmentation: Isolate IoT devices on a separate VLAN to limit lateral movement if compromised.
• Vendor Communication: Contact Semtech for a firmware patch or workaround. Request a CVE update when a fix is released.

Detection Strategy:

• Monitor for unexpected firmware update attempts.
• Log and alert on secure boot failures (if the device reports them).
• Analyze network traffic for anomalous behavior from devices that may indicate compromise.

Indicators of Compromise (IOCs)

• Firmware Hash Mismatch: The hash of the running firmware does not match the expected hash of the last legitimate update.
• Unexpected JTAG/SWD Activity: Unauthorized debug interface access.
• Modified Boot ROM: (Unlikely, but possible if a boot ROM vulnerability exists) Changes to the immutable boot code.
• Anomalous Device Behavior: Unexpected network connections, data exfiltration, or changes in radio frequency behavior.
• Custom Firmware Signatures: Firmware images with valid signatures but containing non-standard payloads.

Detection Engineering

YARA Rule

rule CVE_2025_14859_Semtech_LR11xx_Secure_Boot_Bypass {
    meta:
        description = "Detects firmware images potentially crafted to exploit CVE-2025-14859"
        author = "Valters IT"
        date = "2025-04-10"
        hash = "unknown"
    strings:
        $weak_hash_constant = { 1F 00 00 00 } // Example: constant used in weak hash (e.g., 31)
        $custom_hash_init = { 00 00 00 00 } // Example: hash initialization vector
    condition:
        uint32(0) == 0x464C457F // ELF magic or other firmware header
        and 1 of ($weak_hash_constant, $custom_hash_init)
}

Sigma Rule

title: Potential Exploitation of CVE-2025-14859 - Semtech LR11xx Secure Boot Bypass
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects events that may indicate an attempt to exploit the weak hash in Semtech LR11xx secure boot.
author: Valters IT
date: 2025/04/10
logsource:
    product: linux
    service: auditd
detection:
    selection:
        type: 'ANOM_ABNORMAL'
        key: 'secure_boot'
    condition: selection
falsepositives:
    - Legitimate firmware updates from the vendor.
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-14859 - Potential Firmware Exfiltration from Semtech Device"; flow:to_server; content:"|ff ff ff ff|"; depth:4; content:"firmware"; nocase; within:100; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Devices: Place affected devices on a separate, air-gapped or heavily firewalled network segment.
2. Physical Access Control: Implement strict physical security controls to prevent unauthorized access to devices.
3. Monitor for Anomalies: Enable detailed logging and monitoring for any signs of tampering or unexpected behavior.

Long-Term Fix:

• Vendor Patch: Await an official firmware update from Semtech that replaces the weak hash algorithm with a standard one (e.g., SHA-256). This is the only definitive fix.
• Hardware Revision: For new deployments, request hardware revisions that use a different, secure boot implementation.
• Alternative Secure Boot: If possible, implement an additional layer of secure boot using an external secure element (e.g., TPM, ATECC608) that performs its own signature verification.

Workarounds (if patch is unavailable):

• Code Signing Enforcement: If the device supports it, enforce code signing at the application level, independent of the boot ROM.
• Runtime Attestation: Use a remote attestation server to verify the integrity of devices periodically.

Valters IT

{/* [Security Hash: 1C545BA4C3470D1C54D86720] */}