CVE-2025-66738
📋 TL;DR
A command injection vulnerability in Yealink T21P_E2 phones allows remote attackers with normal privileges to execute arbitrary code via crafted requests to the ping function in the diagnostic component. This affects organizations using vulnerable Yealink phone systems, potentially allowing attackers to compromise phone devices and pivot to internal networks.
💻 Affected Systems
- Yealink T21P_E2 Phone
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full device compromise leading to lateral movement within the network, data exfiltration, and persistent backdoor installation on phone systems.
Likely Case
Attacker gains control of individual phones to eavesdrop on calls, intercept communications, or use as foothold for further attacks.
If Mitigated
Isolated phone VLAN prevents lateral movement; impact limited to individual device compromise.
🎯 Exploit Status
Proof of concept available in referenced Google Drive link; requires authenticated access but normal user privileges are sufficient.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: http://yealink.com
Restart Required: Yes
Instructions:
1. Check Yealink security advisories for firmware updates. 2. Download latest firmware from vendor portal. 3. Upload to phone via web interface or provisioning server. 4. Reboot phone to apply update.
🔧 Temporary Workarounds
Disable Diagnostic Ping Function
allRemove or restrict access to the ping diagnostic function in phone configuration.
Configuration varies by deployment - check Yealink documentation for disabling diagnostic features
Network Segmentation
allIsolate phones on separate VLAN with strict firewall rules preventing external access to diagnostic interfaces.
🧯 If You Can't Patch
- Segment phone network with strict ACLs allowing only necessary SIP/RTP traffic
- Implement network monitoring for unusual outbound connections from phone devices
🔍 How to Verify
Check if Vulnerable:
Check phone firmware version via web interface (Admin > System > Status) or SSH if enabled.Check Version:
Via web: Navigate to http://<phone-ip> and check System Status. Via CLI: ssh admin@<phone-ip> and run 'show version'Verify Fix Applied:
Verify firmware version is updated beyond 52.84.0.15 and test ping function with command injection attempts.📡 Detection & Monitoring
Log Indicators:
- Unusual ping commands with shell metacharacters in phone logs
- Multiple failed authentication attempts followed by successful ping requests
Network Indicators:
- Unusual outbound connections from phones to external IPs
- Traffic patterns inconsistent with normal VoIP operations
SIEM Query:
source="yealink-phone" AND (event="ping" AND command="*;*" OR command="*|*" OR command="*`*")