CVE-2020-3284
📋 TL;DR
This vulnerability allows an unauthenticated remote attacker to execute unsigned code during the PXE boot process on affected Cisco IOS XR devices. Attackers can exploit this by compromising or impersonating the PXE boot server to deliver malicious boot images. Affected systems include Cisco IOS XR 64-bit Software running on specific hardware platforms.
💻 Affected Systems
- Cisco IOS XR 64-bit Software
📦 What is this software?
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⚠️ Risk & Real-World Impact
Worst Case
Complete device compromise allowing persistent malicious code execution at boot time, potentially leading to network-wide compromise, data exfiltration, or service disruption.
Likely Case
Attackers gaining initial foothold on network devices to pivot to other systems, intercept traffic, or disrupt network operations.
If Mitigated
Limited impact if PXE boot is disabled or properly secured with network segmentation and trusted boot servers.
🎯 Exploit Status
Requires network access to PXE boot traffic and ability to compromise or impersonate PXE boot server.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Refer to Cisco Security Advisory for specific fixed releases
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-pxe-unsign-code-exec-qAa78fD2
Restart Required: Yes
Instructions:
1. Upgrade Cisco IOS XR Software to fixed version. 2. Upgrade BIOS using included BIOS code. 3. Reboot device to apply changes. 4. Verify both software and BIOS versions are updated.
🔧 Temporary Workarounds
Disable PXE Network Boot
allConfigure devices to boot from local storage instead of network PXE boot
Configure boot system flash:<image> in global configuration mode
Secure PXE Boot Environment
allImplement network segmentation and access controls for PXE boot traffic
Implement ACLs to restrict PXE boot server access
Use DHCP snooping and IP Source Guard
🧯 If You Can't Patch
- Isolate PXE boot traffic to trusted network segments with strict access controls
- Implement monitoring and alerting for unauthorized PXE boot attempts or server changes
🔍 How to Verify
Check if Vulnerable:
Check Cisco IOS XR version and BIOS version against advisory. Devices using PXE boot with vulnerable versions are affected.Check Version:
show version | include Cisco IOS XR Software, show platformVerify Fix Applied:
Verify both Cisco IOS XR Software and BIOS versions match fixed releases specified in advisory📡 Detection & Monitoring
Log Indicators:
- Unauthorized PXE boot attempts
- Unexpected boot source changes
- BIOS/UEFI firmware modification logs
Network Indicators:
- Unusual PXE/DHCP/TFTP traffic patterns
- PXE boot requests from unexpected sources
SIEM Query:
source="network_device" AND (event="pxe_boot" OR protocol="tftp") AND NOT src_ip IN [trusted_pxe_servers]