CVE-2020-25218
📋 TL;DR
CVE-2020-25218 allows attackers to bypass authentication on Grandstream GRP261x VoIP phones' administrative web interface, granting full administrative access without credentials. This affects organizations using these phones with vulnerable firmware, potentially exposing their VoIP infrastructure to unauthorized control.
💻 Affected Systems
- Grandstream GRP261x VoIP phones
📦 What is this software?
Grp2612 Firmware by Grandstream
Grp2612p Firmware by Grandstream
Grp2612w Firmware by Grandstream
Grp2613 Firmware by Grandstream
Grp2614 Firmware by Grandstream
Grp2615 Firmware by Grandstream
Grp2616 Firmware by Grandstream
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of VoIP infrastructure, call interception, call rerouting, device takeover, and lateral movement to other network systems.
Likely Case
Unauthorized administrative access leading to configuration changes, call monitoring, service disruption, and credential harvesting.
If Mitigated
Limited impact if phones are isolated in separate VLANs with strict network segmentation and access controls.
🎯 Exploit Status
FireEye published detailed technical analysis and exploitation methods. Simple HTTP requests can bypass authentication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware versions after 1.0.3.6
Vendor Advisory: https://www.grandstream.com/support/security-advisories
Restart Required: Yes
Instructions:
1. Download latest firmware from Grandstream support portal. 2. Access phone web interface. 3. Navigate to Maintenance > Upgrade. 4. Upload firmware file. 5. Reboot phone after upgrade completes.
🔧 Temporary Workarounds
Network Segmentation
allIsolate VoIP phones in separate VLAN with strict firewall rules blocking external access to administrative interfaces.
Access Control Lists
allImplement ACLs to restrict access to phone management interfaces to authorized administrative IPs only.
🧯 If You Can't Patch
- Disable administrative web interface if not needed, use alternative management methods
- Implement strict network segmentation and firewall rules to block all external access to phone management ports
🔍 How to Verify
Check if Vulnerable:
Check firmware version via phone web interface: System Status > Device Information > Firmware Version. If version is 1.0.3.6 (Base), device is vulnerable.Check Version:
curl -k https://<phone-ip>/cgi-bin/api-get_system_info or check web interfaceVerify Fix Applied:
After upgrade, verify firmware version shows higher than 1.0.3.6. Test authentication bypass by attempting to access administrative pages without credentials.📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts followed by successful administrative access without valid credentials
- Unauthorized configuration changes in phone logs
Network Indicators:
- HTTP requests to administrative endpoints without authentication headers
- Unusual traffic patterns to phone management ports from unauthorized sources
SIEM Query:
source="voip-phones" AND (event_type="admin_access" AND auth_result="success" AND user="none")