CVE-2024-20353: Cisco ASA Software DOS Vulnerability

CVE-2024-20353 Overview

A vulnerability in the management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to incomplete error checking when parsing an HTTP header. An attacker could exploit this vulnerability by sending a crafted HTTP request to a targeted web server on a device. A successful exploit could allow the attacker to cause a DoS condition when the device reloads.

Critical Impact
This vulnerability can lead to significant disruption in network security operations, affecting the availability of critical network resources.

Affected Products

Cisco Adaptive Security Appliance Software
Cisco Firepower Threat Defense

Discovery Timeline

Not Available - Vulnerability discovered by Not Available
Not Available - Responsible disclosure to Cisco
Not Available - CVE-2024-20353 assigned
Not Available - Cisco releases security patch
2024-04-24 - CVE-2024-20353 published to NVD
2025-10-28 - Last updated in NVD database

Technical Details for CVE-2024-20353

Vulnerability Analysis

The vulnerability arises from a lack of proper error handling while parsing HTTP headers. Malformed HTTP requests can lead the system into a state where it continually reboots, thus entering a denial of service state.

Root Cause

Incomplete error checking during HTTP header parsing results in the system becoming unstable and entering a reload loop.

Attack Vector

Remote attackers can execute the exploit over the network by sending specifically crafted HTTP requests to vulnerable web server interfaces on Cisco ASA and FTD devices.

http

// Example exploitation code (sanitized)
POST / HTTP/1.1
Host: vulnerable.site
Content-Type: application/json
Content-Length: 0
Custom-Header: malformed-request@#$

Detection Methods for CVE-2024-20353

Indicators of Compromise

Unusual server reloads
Repeated service downtime logs
Network traffic containing malformed HTTP requests

Detection Strategies

Network monitoring systems should flag and alert any HTTP requests with malformed headers aimed at ASA or FTD devices. Implement intrusion detection systems (IDS) with rulesets to detect such traffic patterns effectively.

Monitoring Recommendations

Continuously monitor HTTP traffic and server uptime on devices to catch anomalies linked to unexpected reloads. Integrate logging mechanisms to review logs routinely for signs of malformed HTTP traffic.

How to Mitigate CVE-2024-20353

Immediate Actions Required

Disable unnecessary web services on affected devices
Implement network-level restrictions to limit access to management interfaces
Deploy web application firewalls to filter malicious requests

Patch Information

Cisco has released patches to address this vulnerability. Administrators must apply these patches urgently across all affected systems.

Workarounds

While awaiting a patch, consider limiting access to the affected devices' management interfaces from the public internet using network segmentation or VPNs.

bash

# Configuration example
access-list OUTSIDE_IN extended deny tcp any any eq 80
access-list OUTSIDE_IN extended deny tcp any any eq 443
access-group OUTSIDE_IN in interface outside