CVE-2020-3161
📋 TL;DR
CVE-2020-3161 is a critical vulnerability in Cisco IP Phone web servers that allows unauthenticated remote attackers to execute arbitrary code with root privileges or cause denial of service. The vulnerability stems from improper input validation of HTTP requests. Organizations using affected Cisco IP Phone models are at risk.
💻 Affected Systems
- Cisco IP Phone 7800 Series
- Cisco IP Phone 8800 Series
- Cisco IP Phone 8900 Series
- Cisco IP Phone 9900 Series
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Remote attacker gains full root control of IP phone, potentially pivoting to internal networks, intercepting calls, or deploying persistent malware.
Likely Case
Remote denial of service causing phone reboots and service disruption, with potential for limited code execution.
If Mitigated
If phones are isolated in VoIP VLANs with proper network segmentation, impact is limited to phone functionality disruption.
🎯 Exploit Status
Public exploit code available since 2020. Simple HTTP request can trigger vulnerability. CISA lists as known exploited.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware 11.3(1)SR1 and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-voip-phones-rce-dos-rB6EeRXs
Restart Required: Yes
Instructions:
1. Download firmware 11.3(1)SR1 or later from Cisco. 2. Upload to phone TFTP server. 3. Reboot phones to apply update. 4. Verify firmware version after reboot.
🔧 Temporary Workarounds
Disable web access
cisco-voiceDisable the web server interface on affected phones
configure terminal
telephony-service
no web admin
Network segmentation
allIsolate IP phones in separate VLAN with strict access controls
🧯 If You Can't Patch
- Implement strict network segmentation - place phones in isolated VoIP VLAN with no internet access
- Deploy network-based IPS/IDS rules to detect and block exploit attempts
🔍 How to Verify
Check if Vulnerable:
Check phone firmware version via web interface or phone settings menu. Versions below 11.3(1)SR1 are vulnerable.Check Version:
From phone: Settings > Status > Firmware Information. From CLI: show versionVerify Fix Applied:
Verify firmware version is 11.3(1)SR1 or later. Test web interface functionality remains operational.📡 Detection & Monitoring
Log Indicators:
- Multiple HTTP 400/500 errors from phone web server
- Unexpected phone reboots in logs
- Unusual HTTP requests to phone web interface
Network Indicators:
- HTTP POST requests with malformed headers to phone IPs
- Sudden spike in phone reboot events
- Traffic to phone web interface from unexpected sources
SIEM Query:
source="phone_logs" AND (http_status>=400 OR event="reboot") | stats count by src_ip, dest_ip🔗 References
- http://packetstormsecurity.com/files/157265/Cisco-IP-Phone-11.7-Denial-Of-Service.html
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-voip-phones-rce-dos-rB6EeRXs
- http://packetstormsecurity.com/files/157265/Cisco-IP-Phone-11.7-Denial-Of-Service.html
- https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-voip-phones-rce-dos-rB6EeRXs
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-3161
