CVE-2020-3574
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to cause Cisco IP Phones to stop responding to calls, drop active calls, or reboot by flooding them with crafted TCP packets. It affects Cisco IP Phone models running vulnerable firmware due to insufficient TCP rate limiting. Organizations using affected Cisco VoIP phones are at risk of service disruption.
💻 Affected Systems
- Cisco IP Phone 7800 Series
- Cisco IP Phone 8800 Series
- Cisco Video Phone 8875
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of VoIP services across an organization, disrupting business communications and operations.
Likely Case
Intermittent call drops and phone reboots affecting user productivity and call quality.
If Mitigated
Minimal impact with proper network segmentation and rate limiting controls in place.
🎯 Exploit Status
Simple TCP flood attack requiring only network access to target phone.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firmware 12.8(1)SR1 and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-voip-phone-flood-dos-YnU9EXOv
Restart Required: Yes
Instructions:
1. Download firmware 12.8(1)SR1 or later from Cisco. 2. Upload to phone via TFTP/HTTP. 3. Reboot phone to apply update. 4. Verify firmware version post-update.
🔧 Temporary Workarounds
Network Segmentation
allIsolate VoIP network from untrusted networks to limit attack surface.
Rate Limiting
allImplement TCP rate limiting on network devices protecting VoIP segment.
🧯 If You Can't Patch
- Segment VoIP phones on isolated VLAN with strict ACLs
- Implement network-based DDoS protection with TCP flood mitigation
🔍 How to Verify
Check if Vulnerable:
Check phone firmware version via phone UI: Settings > Status > Firmware VersionsCheck Version:
From phone: Press Settings button > Status > Firmware VersionsVerify Fix Applied:
Confirm firmware version is 12.8(1)SR1 or later and test phone functionality📡 Detection & Monitoring
Log Indicators:
- Phone reboot logs
- High TCP connection attempts
- Call drop events
Network Indicators:
- Unusual high-volume TCP traffic to VoIP subnet
- TCP SYN floods targeting port 80/5060
SIEM Query:
source="voip-phones" AND (event="reboot" OR event="call_drop") AND tcp_count > threshold