CVE-2020-3444
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to bypass layer 3 and layer 4 traffic filters in Cisco SD-WAN Software by sending specially crafted TCP packets. This could enable attackers to inject arbitrary packets into protected networks. Organizations using affected Cisco SD-WAN devices are impacted.
💻 Affected Systems
- Cisco SD-WAN vEdge Routers
- Cisco SD-WAN vSmart Controllers
- Cisco SD-WAN vManage
📦 What is this software?
Ios Xe by Cisco
Cisco IOS XE is Cisco's modern network operating system running on enterprise routers, switches, and wireless controllers deployed across corporate networks, data centers, branch offices, and service provider infrastructure worldwide. As the evolution of Cisco IOS, IOS XE provides a Linux-based modu...
Learn more about Ios Xe →Ios Xe by Cisco
Cisco IOS XE is Cisco's modern network operating system running on enterprise routers, switches, and wireless controllers deployed across corporate networks, data centers, branch offices, and service provider infrastructure worldwide. As the evolution of Cisco IOS, IOS XE provides a Linux-based modu...
Learn more about Ios Xe →⚠️ Risk & Real-World Impact
Worst Case
Attackers could bypass all L3/L4 filtering to inject malicious traffic, potentially enabling lateral movement, data exfiltration, or service disruption within protected network segments.
Likely Case
Attackers bypass specific traffic filters to send unauthorized packets, potentially enabling reconnaissance, data leakage, or circumventing security controls.
If Mitigated
With proper network segmentation and additional security controls, impact is limited to potential bypass of specific filtering rules rather than full network compromise.
🎯 Exploit Status
Exploitation requires crafting specific TCP packets but does not require authentication. No public exploit code has been released.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Cisco SD-WAN Software release 20.3.1 or later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-cedge-filt-bypass-Y6wZMqm4
Restart Required: Yes
Instructions:
1. Download Cisco SD-WAN Software release 20.3.1 or later from Cisco Software Center. 2. Upload the software to affected devices. 3. Install the update following Cisco SD-WAN upgrade procedures. 4. Reboot devices to activate the new software.
🔧 Temporary Workarounds
Implement additional network controls
allDeploy additional firewall rules or network segmentation to compensate for potential filter bypass
🧯 If You Can't Patch
- Implement strict network segmentation to limit potential impact if filters are bypassed
- Deploy additional layer 7 security controls (WAF, IPS) to detect and block malicious traffic that might bypass L3/L4 filters
🔍 How to Verify
Check if Vulnerable:
Check Cisco SD-WAN software version using 'show version' command. If version is earlier than 20.3.1, the device is vulnerable.Check Version:
show version | include SoftwareVerify Fix Applied:
After patching, verify version is 20.3.1 or later using 'show version' command and test packet filtering functionality.📡 Detection & Monitoring
Log Indicators:
- Unexpected traffic patterns bypassing configured filters
- TCP packets with unusual characteristics in network logs
Network Indicators:
- TCP packets with crafted characteristics attempting to bypass filters
- Traffic appearing from unexpected sources despite filter rules
SIEM Query:
source_ip NOT IN allowed_ips AND protocol=tcp AND (tcp_flags unusual OR packet_size abnormal)