CVE-2021-34795
📋 TL;DR
This critical vulnerability in Cisco Catalyst PON Series Switches ONT web management interface allows unauthenticated remote attackers to log in with default credentials, execute arbitrary commands, and modify configurations. It affects organizations using these specific Cisco optical network switches with vulnerable configurations. The CVSS 10.0 score indicates maximum severity.
💻 Affected Systems
- Cisco Catalyst PON Series Switches Optical Network Terminal (ONT)
📦 What is this software?
Catalyst Pon Switch Cgp Ont 1p Firmware by Cisco
View all CVEs affecting Catalyst Pon Switch Cgp Ont 1p Firmware →
Catalyst Pon Switch Cgp Ont 4p Firmware by Cisco
View all CVEs affecting Catalyst Pon Switch Cgp Ont 4p Firmware →
Catalyst Pon Switch Cgp Ont 4pv Firmware by Cisco
View all CVEs affecting Catalyst Pon Switch Cgp Ont 4pv Firmware →
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of network infrastructure allowing attacker to reconfigure switches, intercept traffic, deploy malware, and potentially pivot to other network segments.
Likely Case
Unauthorized access leading to configuration changes, service disruption, and potential credential harvesting from connected systems.
If Mitigated
Limited impact if proper network segmentation, access controls, and updated firmware are in place.
🎯 Exploit Status
Multiple attack vectors including default credentials and command injection make exploitation straightforward for attackers with network access
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Check Cisco advisory for specific fixed versions
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-catpon-multivulns-CE3DSYGr
Restart Required: Yes
Instructions:
1. Review Cisco advisory for affected versions 2. Download appropriate firmware update 3. Backup configuration 4. Apply firmware update following Cisco documentation 5. Verify update and restore configuration if needed
🔧 Temporary Workarounds
Disable Telnet Protocol
allPrevents default credential login vulnerability by disabling Telnet access
no telnet enable
Restrict Management Interface Access
allLimit access to management interface using ACLs
access-list 100 permit ip [trusted-network] any
interface [management-interface]
ip access-group 100 in
🧯 If You Can't Patch
- Isolate affected switches in separate VLAN with strict firewall rules
- Implement network monitoring for suspicious access attempts to management interfaces
🔍 How to Verify
Check if Vulnerable:
Check device firmware version against Cisco advisory and verify if Telnet is enabledCheck Version:
show versionVerify Fix Applied:
Confirm firmware version is updated to patched version and test for vulnerability📡 Detection & Monitoring
Log Indicators:
- Failed authentication attempts
- Unexpected configuration changes
- Telnet access from unauthorized sources
Network Indicators:
- Unusual traffic patterns to management interfaces
- Telnet connections to switch management IPs
SIEM Query:
source_ip="[switch_management_ip]" AND (protocol="telnet" OR port=23) AND action="denied"