CVE-2025-47187: Mitel SIP Phones Auth Bypass Vulnerability

CVE-2025-47187 Overview

A vulnerability exists in the Mitel 6800 Series, 6900 Series, and 6900w Series SIP Phones through version 6.4 SP4 (R6.4.0.4006), as well as the 6970 Conference Unit through 6.4 SP4 (R6.4.0.4006) or version V1 R0.1.0. This flaw allows an unauthenticated attacker to perform a file upload attack due to missing authentication mechanisms. A successful exploit enables an attacker to upload arbitrary WAV files, which may potentially exhaust the phone's storage resources.

Critical Impact

Unauthenticated remote attackers can upload arbitrary WAV files to Mitel SIP phones, potentially exhausting device storage and enabling denial of service conditions on enterprise communication infrastructure.

Affected Products

• Mitel 6800 Series SIP Phones through version 6.4 SP4 (R6.4.0.4006)
• Mitel 6900 Series SIP Phones through version 6.4 SP4 (R6.4.0.4006)
• Mitel 6900w Series SIP Phones through version 6.4 SP4 (R6.4.0.4006)
• Mitel 6970 Conference Unit through version 6.4 SP4 (R6.4.0.4006) or V1 R0.1.0

Discovery Timeline

• 2025-07-23 - CVE-2025-47187 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-47187

Vulnerability Analysis

This vulnerability is classified as CWE-434 (Unrestricted Upload of File with Dangerous Type), though in this specific case the impact is limited to storage exhaustion rather than code execution. The affected Mitel SIP phones lack proper authentication controls on their file upload functionality, allowing any network-accessible attacker to upload files to the device without credentials.

The vulnerability is network-accessible and requires no user interaction or privileges to exploit. While the description indicates the phone's availability and operation are not directly affected, the potential for storage exhaustion could lead to degraded functionality over time as device storage becomes saturated with attacker-uploaded WAV files.

Root Cause

The root cause of this vulnerability is the absence of authentication mechanisms protecting the file upload endpoint on affected Mitel SIP phones. The upload functionality accepts WAV file uploads without verifying the identity or authorization of the requesting party, creating an open attack surface for any network-adjacent or remote attacker who can reach the device.

Attack Vector

The attack leverages the network-accessible file upload functionality present on affected Mitel SIP phones. An attacker can remotely connect to a vulnerable device and upload arbitrary WAV files without authentication. The attack flow typically involves:

1. Network reconnaissance to identify Mitel SIP phones on the target network
2. Identification of the unauthenticated file upload endpoint
3. Repeated upload of WAV files to exhaust available device storage
4. Potential degradation of phone functionality as storage capacity is consumed

This attack can be conducted from anywhere on the network with connectivity to the vulnerable devices, making it particularly concerning for enterprises with internet-exposed or poorly segmented VoIP infrastructure.

Detection Methods for CVE-2025-47187

Indicators of Compromise

• Unexpected increase in storage utilization on Mitel SIP phones
• Presence of unknown or suspicious WAV files on affected devices
• Network traffic patterns showing repeated file uploads to phone devices from unauthorized sources
• Log entries indicating file upload activities from external or unexpected IP addresses

Detection Strategies

• Monitor network traffic for HTTP/HTTPS requests to Mitel SIP phone file upload endpoints
• Implement network segmentation monitoring to detect unauthorized access attempts to VoIP infrastructure
• Deploy network intrusion detection signatures for Mitel SIP phone file upload patterns
• Audit device storage levels on Mitel phones for unexpected consumption

Monitoring Recommendations

• Establish baseline storage utilization metrics for Mitel SIP phones and alert on anomalies
• Configure network monitoring to flag upload requests to VoIP devices from non-management subnets
• Review device logs regularly for signs of unauthorized file upload activity
• Implement SIEM correlation rules for detecting potential storage exhaustion attacks on communication devices

How to Mitigate CVE-2025-47187

Immediate Actions Required

• Review network segmentation to ensure Mitel SIP phones are not directly accessible from untrusted networks
• Implement network-level access controls (firewalls, ACLs) to restrict access to phone management interfaces
• Monitor affected devices for signs of exploitation or unusual storage consumption
• Consult Mitel Security Advisory MISA-2025-0004 for vendor-specific guidance

Patch Information

Mitel has released a security advisory addressing this vulnerability. Organizations should consult Mitel Security Advisories and the specific advisory MISA-2025-0004 for information on available patches and firmware updates for affected devices. Administrators should prioritize upgrading affected Mitel SIP phones and Conference Units beyond version 6.4 SP4 (R6.4.0.4006) to remediate this vulnerability.

Workarounds

• Implement network-level access controls to restrict file upload functionality to authorized management stations only
• Deploy network segmentation to isolate VoIP infrastructure from general user networks and untrusted zones
• Enable network monitoring and alerting for unauthorized access attempts to Mitel devices
• Consider implementing web application firewalls or reverse proxies with authentication in front of phone management interfaces

# Example network ACL to restrict access to Mitel phones (Cisco IOS syntax)
# Adjust IP ranges for your environment
access-list 101 permit tcp 10.0.100.0 0.0.0.255 10.0.200.0 0.0.0.255 eq 443
access-list 101 permit tcp 10.0.100.0 0.0.0.255 10.0.200.0 0.0.0.255 eq 80
access-list 101 deny tcp any 10.0.200.0 0.0.0.255 eq 443
access-list 101 deny tcp any 10.0.200.0 0.0.0.255 eq 80
# 10.0.100.0/24 = Management subnet
# 10.0.200.0/24 = VoIP phone subnet