CVE-2025-66737
📋 TL;DR
Yealink T21P_E2 phones running firmware 52.84.0.15 have a directory traversal vulnerability in the diagnostic component. Remote attackers with normal privileges can read arbitrary files on the device by crafting malicious requests. This affects organizations using these specific VoIP phones in their networks.
💻 Affected Systems
- Yealink T21P_E2 Phone
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Attackers could read sensitive configuration files, credentials, or system files, potentially enabling further attacks or data exfiltration.
Likely Case
Attackers read configuration files to gather network information or credentials for lateral movement within the VoIP network.
If Mitigated
With proper network segmentation and access controls, impact is limited to the compromised device only.
🎯 Exploit Status
Exploitation requires authenticated access but uses normal user privileges. Crafted requests to diagnostic component can traverse directories.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Unknown
Vendor Advisory: http://yealink.com
Restart Required: Yes
Instructions:
1. Check Yealink website for security advisories
2. Download latest firmware if available
3. Upload firmware to phone via web interface
4. Reboot phone after update
🔧 Temporary Workarounds
Disable Diagnostic Access
allRestrict access to diagnostic component via network controls
Network Segmentation
allIsolate VoIP phones in separate VLAN with restricted access
🧯 If You Can't Patch
- Segment VoIP network from critical infrastructure
- Implement strict access controls to phone management interfaces
🔍 How to Verify
Check if Vulnerable:
Check phone firmware version via web interface at System > Status > VersionCheck Version:
curl -s http://phone-ip/cgi-bin/version.cgiVerify Fix Applied:
Verify firmware version is updated beyond 52.84.0.15📡 Detection & Monitoring
Log Indicators:
- Unusual file access patterns in diagnostic logs
- Multiple failed directory traversal attempts
Network Indicators:
- HTTP requests with ../ sequences to diagnostic endpoints
- Unusual file read patterns from phone IP
SIEM Query:
source="voip_logs" AND (uri="*../*" OR method="GET" AND uri="*/cgi-bin/diagnostic*")