CVE-2024-20467
📋 TL;DR
An unauthenticated remote attacker can cause Cisco routers to crash and reload by sending specially crafted fragmented IPv4 packets, resulting in denial of service. This affects Cisco ASR 1000 Series and cBR-8 routers running specific IOS XE versions with vulnerable fragmentation reassembly code.
💻 Affected Systems
- Cisco ASR 1000 Series Aggregation Services Routers
- Cisco cBR-8 Converged Broadband Routers
📦 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 →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
Router crashes and reloads, causing complete network outage for all traffic passing through the affected device until it restarts.
Likely Case
Router experiences repeated crashes and reloads when targeted with fragmented packets, causing intermittent network outages.
If Mitigated
With proper network segmentation and access controls, only authorized traffic reaches the router, reducing exposure to potential attacks.
🎯 Exploit Status
Exploitation requires sending specific sizes of fragmented packets to trigger the resource management vulnerability.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Upgrade to a fixed release (not specified in advisory, check vendor advisory for specific fixed versions)
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-cpp-vfr-dos-nhHKGgO
Restart Required: Yes
Instructions:
1. Check current IOS XE version. 2. Download appropriate fixed software from Cisco. 3. Backup configuration. 4. Install update following Cisco IOS XE upgrade procedures. 5. Reboot device.
🔧 Temporary Workarounds
Disable VFR on interfaces
cisco-iosDisable Virtual Fragmentation Reassembly on interfaces where it's not required to mitigate the vulnerability.
interface <interface_name>
no ip virtual-reassembly
🧯 If You Can't Patch
- Implement strict access control lists (ACLs) to limit which sources can send fragmented packets to vulnerable interfaces.
- Use network segmentation to isolate vulnerable routers from untrusted networks and limit attack surface.
🔍 How to Verify
Check if Vulnerable:
Check IOS XE version with 'show version' and verify if running 17.12.1 or 17.12.1a on affected hardware platforms.Check Version:
show version | include VersionVerify Fix Applied:
After upgrade, verify new version with 'show version' and confirm it's not 17.12.1 or 17.12.1a.📡 Detection & Monitoring
Log Indicators:
- Router reload messages in system logs
- Unexpected crashes or reboots
- High CPU/memory usage before crash
Network Indicators:
- Unusual fragmented packet traffic to router interfaces
- Sudden loss of connectivity through router
SIEM Query:
source="router_logs" AND ("reload" OR "crash" OR "%SYS-5-RESTART")