CVE-2024-20481: Cisco Firepower Threat Defense DoS Flaw

CVE-2024-20481 Overview

A vulnerability in the Remote Access VPN (RAVPN) service of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) of the RAVPN service. This vulnerability is due to resource exhaustion. An attacker could exploit this vulnerability by sending a large number of VPN authentication requests to an affected device. A successful exploit could allow the attacker to exhaust resources, resulting in a DoS of the RAVPN service on the affected device. Depending on the impact of the attack, a reload of the device may be required to restore the RAVPN service. Services that are not related to VPN are not affected.

Critical Impact

This vulnerability can be exploited to cause a significant disruption of VPN services, necessitating a device reboot to restore functionality.

Affected Products

• Cisco Adaptive Security Appliance Software
• Cisco Firepower Threat Defense Software
• Not Available

Discovery Timeline

• Not Available - Vulnerability discovered by Not Available
• Not Available - Responsible disclosure to Cisco
• Not Available - CVE CVE-2024-20481 assigned
• Not Available - Cisco releases security patch
• 2024-10-23 - CVE CVE-2024-20481 published to NVD
• 2025-10-28 - Last updated in NVD database

Technical Details for CVE-2024-20481

Vulnerability Analysis

The RAVPN service of Cisco ASA and FTD software is susceptible to an attack vector that exploits a resource exhaustion flaw. The unauthenticated attacker can inundate the VPN service with numerous authentication requests, overwhelming the device’s processing capacity and leading to a service outage.

Root Cause

This issue arises due to insufficient handling of authentication requests, leading to resource exhaustion.

Attack Vector

This vulnerability can be exploited remotely via the network by sending a high volume of VPN authentication requests.

# Example exploitation code (sanitized)
#!/bin/bash

for i in {1..10000}
do
  curl -X POST http://vulnerable-device/vpn/connect --data "username=attacker&password=password"
done

Detection Methods for CVE-2024-20481

Indicators of Compromise

• Unusual spikes in VPN authentication logs
• Sudden unavailability of RAVPN services
• System reloads without administrator input

Detection Strategies

Employ network monitoring solutions to detect abnormal patterns in authentication requests. Configure threshold alerts for high volumes of login attempts within a short period.

Monitoring Recommendations

Utilize SentinelOne’s behavioral AI to continuously monitor network traffic for anomalous authentication activity that could indicate an impending DoS attack.

How to Mitigate CVE-2024-20481

Immediate Actions Required

• Rate-limit VPN authentication attempts.
• Implement CAPTCHA or similar challenges to mitigate automated attack scripts.
• Increase the logging and alerting mechanisms for VPN services.

Patch Information

Please refer to the Vendor Advisory for patch details.

Workarounds

Consider throttling or blocking IP addresses that exhibit anomalous behavior patterns indicative of a resource exhaustion attempt until a patch can be applied.

# Configuration example
iptables -A INPUT -p tcp --syn -dport 443 -m limit --limit 25/minute --limit-burst 100 -j ACCEPT