CVE-2025-20350
📋 TL;DR
A buffer overflow vulnerability in Cisco phone web interfaces allows unauthenticated remote attackers to cause denial of service by sending crafted HTTP packets. This affects Cisco Desk Phone 9800 Series, IP Phone 7800/8800 Series, and Video Phone 8875 running Cisco SIP Software. Exploitation requires the phone to be registered to Cisco Unified Communications Manager with Web Access enabled.
💻 Affected Systems
- Cisco Desk Phone 9800 Series
- Cisco IP Phone 7800 Series
- Cisco IP Phone 8800 Series
- Cisco Video Phone 8875
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Persistent DoS attacks could render critical communication devices unusable, disrupting business operations and emergency communications.
Likely Case
Temporary service disruption causing phone reboots and dropped calls until devices reload.
If Mitigated
Minimal impact if Web Access is disabled or devices are behind proper network segmentation.
🎯 Exploit Status
Exploitation requires sending crafted HTTP packets to vulnerable web interface. No authentication needed once Web Access is enabled.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco Security Advisory for specific firmware updates
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-phone-dos-FPyjLV7A
Restart Required: Yes
Instructions:
1. Review Cisco Security Advisory for affected firmware versions. 2. Download and apply recommended firmware updates from Cisco. 3. Reboot affected phones after update. 4. Verify Web Access settings post-update.
🔧 Temporary Workarounds
Disable Web Access
allDisable the web interface on affected phones to prevent HTTP-based exploitation
Configure via Cisco Unified Communications Manager: Device > Phone > Web Access > Disabled
Network Segmentation
linuxRestrict network access to phone web interfaces using firewall rules
iptables -A INPUT -p tcp --dport 80 -s trusted_networks -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s trusted_networks -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -j DROP
🧯 If You Can't Patch
- Disable Web Access on all affected phones immediately
- Implement strict network segmentation to isolate phone traffic from untrusted networks
🔍 How to Verify
Check if Vulnerable:
Check phone firmware version against Cisco advisory and verify Web Access is enabled in Cisco Unified Communications ManagerCheck Version:
On phone: Settings > Status > Firmware Information or via Cisco Unified Communications ManagerVerify Fix Applied:
Verify firmware version is updated to patched version and test HTTP access to phone web interface📡 Detection & Monitoring
Log Indicators:
- Multiple HTTP connection attempts to phone web interface
- Phone reboot logs without normal shutdown sequence
- Unusual HTTP request patterns to phone IP addresses
Network Indicators:
- HTTP traffic to phone web interfaces from unexpected sources
- Multiple TCP connections to phone port 80/443 followed by device unreachable
SIEM Query:
source="phone_logs" AND (event="reboot" OR event="crash") AND http_request EXISTS