CVE-2025-20209 Overview
A denial of service vulnerability exists in the Internet Key Exchange version 2 (IKEv2) function of Cisco IOS XR Software. This vulnerability could allow an unauthenticated, remote attacker to prevent an affected device from processing any control plane UDP packets, resulting in a complete loss of critical network management and routing protocol functionality.
The vulnerability stems from improper handling of malformed IKEv2 packets. An attacker can exploit this flaw by sending specially crafted IKEv2 packets to an affected device, causing the device to stop processing control plane UDP traffic. This impacts a wide range of Cisco IOS XR versions spanning from 6.5.1 through 24.2.11, affecting critical network infrastructure devices.
Critical Impact
Successful exploitation allows remote attackers to cause a denial of service condition affecting all control plane UDP packet processing, potentially disrupting routing protocols, network management, and VPN connectivity on affected Cisco IOS XR devices.
Affected Products
- Cisco IOS XR Software (versions 6.5.1 through 24.2.11)
- Cisco NCS 1004, NCS 1010, NCS 1014 (Network Convergence System platforms)
- Cisco NCS 540L (Compact NCS router series)
Discovery Timeline
- March 12, 2025 - CVE-2025-20209 published to NVD
- August 1, 2025 - Last updated in NVD database
Technical Details for CVE-2025-20209
Vulnerability Analysis
This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling). The IKEv2 implementation in Cisco IOS XR Software fails to properly validate and handle malformed IKEv2 packets, leading to a condition where the affected device stops processing control plane UDP packets entirely.
The impact of this vulnerability is significant because control plane UDP packets are essential for numerous critical network functions including routing protocol communications (BGP, OSPF), network management (SNMP), DNS resolution, and VPN establishment. When an attacker successfully exploits this vulnerability, the affected device becomes unable to maintain routing adjacencies, respond to management queries, or establish new VPN tunnels.
The attack requires no authentication and can be launched remotely over the network, making it particularly dangerous for Internet-facing Cisco IOS XR devices with IKEv2 services enabled. The vulnerability affects devices used in service provider and enterprise backbone networks, where a single compromised device can have cascading effects on network stability.
Root Cause
The root cause of CVE-2025-20209 lies in the improper handling of malformed IKEv2 packets within the IKEv2 processing function of Cisco IOS XR Software. The software fails to properly validate IKEv2 packet structures before processing, resulting in a resource allocation issue that prevents subsequent control plane UDP packet processing. This is a classic CWE-770 condition where resources are allocated without proper limits or throttling mechanisms.
Attack Vector
The attack vector for this vulnerability is network-based, requiring no user interaction or authentication. An attacker can exploit this vulnerability by:
- Identifying a target Cisco IOS XR device with IKEv2 services enabled
- Crafting malformed IKEv2 packets designed to trigger the improper handling condition
- Sending the malicious packets to the target device's IKEv2 service port (UDP 500 or UDP 4500)
- Upon successful exploitation, the device stops processing all control plane UDP packets
The attack is particularly effective because IKEv2 is commonly used for IPsec VPN establishment, and the service is often exposed on perimeter devices. Once exploited, the denial of service condition affects the entire control plane UDP processing capability, not just IKEv2 functions.
Detection Methods for CVE-2025-20209
Indicators of Compromise
- Sudden loss of routing protocol adjacencies (BGP, OSPF, ISIS) across multiple protocols simultaneously
- Network management systems reporting unreachable devices via SNMP polling failures
- VPN tunnel establishment failures combined with control plane unresponsiveness
- Syslog messages indicating IKEv2 processing errors or anomalies prior to the outage
Detection Strategies
- Monitor for unusual volumes of IKEv2 traffic (UDP ports 500, 4500) from unexpected sources
- Deploy network-based intrusion detection signatures for malformed IKEv2 packet patterns
- Implement baseline monitoring for control plane UDP packet processing metrics on IOS XR devices
- Configure alerts for simultaneous routing protocol neighbor state changes across multiple protocols
Monitoring Recommendations
- Enable detailed logging for IKEv2 events and control plane activities on potentially affected devices
- Implement NetFlow or IPFIX collection to identify anomalous traffic patterns targeting UDP ports 500 and 4500
- Establish baseline metrics for control plane health and configure thresholds for automated alerting
- Monitor for signs of reconnaissance activity targeting IKEv2 services across the network perimeter
How to Mitigate CVE-2025-20209
Immediate Actions Required
- Identify all Cisco IOS XR devices running affected versions (6.5.1 through 24.2.11) in your environment
- Apply the security patch released by Cisco as soon as possible following your change management process
- Implement access control lists (ACLs) to restrict IKEv2 traffic to authorized sources only
- Review and harden control plane protection policies to limit exposure of the IKEv2 service
Patch Information
Cisco has released software updates that address this vulnerability. Organizations should consult the Cisco Security Advisory (cisco-sa-xrike-9wYGpRGq) for specific fixed software versions and upgrade guidance. The advisory provides detailed information on the appropriate fixed release for each affected software version.
According to the Cisco advisory, there are no workarounds that fully address this vulnerability, making software upgrades the primary remediation approach.
Workarounds
- Deploy infrastructure ACLs (iACLs) to restrict IKEv2 traffic to only known and trusted sources
- Implement Control Plane Policing (CoPP) to rate-limit IKEv2 traffic and reduce the potential impact of exploitation attempts
- Consider disabling IKEv2 services on devices where they are not actively required
- Segment network architecture to limit attacker access to vulnerable control plane services
# Example infrastructure ACL configuration to restrict IKEv2 access
# Apply to interfaces facing untrusted networks
ipv4 access-list PROTECT-IKEV2
10 permit udp host <trusted-peer-1> any eq 500
20 permit udp host <trusted-peer-1> any eq 4500
30 permit udp host <trusted-peer-2> any eq 500
40 permit udp host <trusted-peer-2> any eq 4500
50 deny udp any any eq 500 log
60 deny udp any any eq 4500 log
70 permit ipv4 any any
# Apply to interface
interface GigabitEthernet0/0/0/0
ipv4 access-group PROTECT-IKEV2 ingress
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
