CVE-2024-20455 Overview
A denial of service vulnerability exists in the Unified Threat Defense (UTD) component of Cisco IOS XE Software operating in controller mode. The vulnerability stems from improper handling of certain packets as they egress an SD-WAN IPsec tunnel. An unauthenticated, remote attacker can exploit this flaw by sending specially crafted traffic through an SD-WAN IPsec tunnel configured on an affected device, causing the device to reload and resulting in a complete denial of service condition.
This vulnerability specifically affects the traffic classification process within the UTD component. It is important to note that SD-WAN tunnels configured with Generic Routing Encapsulation (GRE) are not affected by this vulnerability.
Critical Impact
Successful exploitation allows an unauthenticated remote attacker to cause complete device reload, disrupting all network services and potentially affecting critical infrastructure connectivity.
Affected Products
- Cisco IOS XE versions 17.1.x through 17.13.x (controller mode)
- Cisco IOS XE SD-WAN versions 17.5.1a through 17.13.1a
- Devices configured with SD-WAN IPsec tunnels and UTD enabled
Discovery Timeline
- September 25, 2024 - CVE-2024-20455 published to NVD
- October 24, 2024 - Last updated in NVD database
Technical Details for CVE-2024-20455
Vulnerability Analysis
This denial of service vulnerability resides in the traffic classification mechanism of the Unified Threat Defense (UTD) component within Cisco IOS XE Software. When the software operates in controller mode with SD-WAN IPsec tunnels configured, the UTD component fails to properly handle certain malformed or specially crafted packets during the egress processing phase.
The vulnerability allows an unauthenticated attacker with network access to the SD-WAN IPsec tunnel to trigger a complete device reload without requiring any privileges or user interaction. The impact extends beyond the targeted device as it can affect the overall network topology and routing convergence, particularly in environments where the affected device serves as a critical network node.
The attack can be launched remotely across the network, making it particularly dangerous for internet-facing or branch office deployments using SD-WAN architecture.
Root Cause
The root cause of this vulnerability lies in the improper input validation and packet handling within the UTD traffic classification process. When processing packets that egress through SD-WAN IPsec tunnels, the UTD component encounters an unhandled exception or memory condition when specific packet characteristics are present. This causes the device to enter an unrecoverable state, forcing a reload.
The issue is specific to IPsec-based SD-WAN tunnels; GRE-based tunnels process packets through a different code path that does not exhibit this vulnerability.
Attack Vector
The attack vector for CVE-2024-20455 involves:
- Network Access: The attacker must be able to send traffic through an SD-WAN IPsec tunnel configured on the target device
- Crafted Packets: Specially crafted packets are sent through the tunnel that trigger the vulnerability during UTD processing
- No Authentication Required: The attack does not require any form of authentication or valid credentials
- No User Interaction: Exploitation is entirely automated and requires no user interaction
The attack can be executed by any attacker who can route traffic through the vulnerable SD-WAN IPsec tunnel, including from remote network segments or through compromised internal hosts.
Detection Methods for CVE-2024-20455
Indicators of Compromise
- Unexpected device reloads with crash logs indicating UTD component failures
- Syslog messages showing abnormal traffic patterns on SD-WAN IPsec interfaces
- Repeated device restarts correlating with specific traffic flows through IPsec tunnels
- Core dump files indicating memory corruption or exception handling in UTD processes
Detection Strategies
- Monitor device syslog for crash events and unexpected reloads, specifically noting references to UTD or traffic classification processes
- Implement NetFlow or network telemetry to identify anomalous packet patterns targeting SD-WAN IPsec tunnel interfaces
- Configure SNMP traps for device reload events and establish baseline reload frequency for comparison
- Deploy network intrusion detection systems to monitor for malformed packets destined for SD-WAN tunnel endpoints
Monitoring Recommendations
- Enable continuous monitoring of device availability and reload events across all Cisco IOS XE devices in SD-WAN deployments
- Implement centralized logging with correlation rules to detect patterns of device failures that may indicate active exploitation
- Configure alerting for any UTD-related errors or exceptions in device logs
- Regularly review crash information to identify potential exploitation attempts
How to Mitigate CVE-2024-20455
Immediate Actions Required
- Review your Cisco IOS XE inventory to identify all devices running affected versions with SD-WAN IPsec tunnels and UTD enabled
- Prioritize patching for devices that are internet-facing or serve critical network functions
- Consider temporarily switching affected tunnels to GRE encapsulation as a workaround, as GRE tunnels are not affected
- Implement network segmentation to limit potential attacker access to SD-WAN tunnel endpoints
Patch Information
Cisco has released security updates to address this vulnerability. Administrators should consult the Cisco Security Advisory cisco-sa-sdwan-utd-dos-hDATqxs for specific fixed software versions and upgrade guidance. The advisory provides detailed information about affected and fixed releases for both Cisco IOS XE and Cisco IOS XE SD-WAN.
Organizations should follow their standard change management procedures and test updates in non-production environments before deploying to critical infrastructure.
Workarounds
- Migrate affected SD-WAN tunnels from IPsec to GRE encapsulation where operationally feasible, as GRE tunnels are not vulnerable
- Implement access control lists (ACLs) to restrict which sources can send traffic through SD-WAN IPsec tunnels
- Consider temporarily disabling UTD on affected devices if the security inspection functionality is not critical, while awaiting patching
- Deploy rate limiting on tunnel interfaces to reduce the potential impact of exploitation attempts
# Example: Verify UTD status and tunnel configuration
show utd engine standard status
show sdwan control connections
show ip interface brief | include Tunnel
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
