Cisco ASA and FTD Buffer Overflow (CVE-2025-20263): Brief Summary and Patch Guidance

Introduction

A single crafted HTTP request can force a Cisco firewall to reload, disrupting network traffic and exposing organizations to denial of service. CVE-2025-20263 is a buffer overflow vulnerability in Cisco Secure Firewall Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) Software, affecting a critical component relied upon by enterprises and service providers worldwide.

Cisco is a dominant force in the networking and security appliance market. Its ASA and FTD product lines are deployed in countless enterprise, government, and critical infrastructure environments, acting as the backbone of perimeter defense for millions of networks.

Technical Information

CVE-2025-20263 is caused by insufficient boundary checks in the web services interface of Cisco ASA and FTD Software. The vulnerability is classified as CWE-680 (Integer Overflow to Buffer Overflow). When the web services interface receives certain crafted HTTP requests, improper integer calculations during buffer allocation can result in a buffer that is too small for the incoming data. The subsequent overflow corrupts memory and causes the device to reload, resulting in a denial of service.

Key technical points:

• Attackers do not need to authenticate. Any remote attacker can exploit the flaw by sending a specially crafted HTTP request to the web services interface.
• The root cause is insufficient boundary checking on input data, specifically in the logic that calculates buffer sizes for HTTP request handling.
• Exploitation leads to a system reload, disrupting firewall operations and potentially impacting all connected networks.
• No public code snippets or PoCs are available for this vulnerability.

Patch Information

To address the buffer overflow vulnerability in the web services interface of Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software, Cisco has released software updates that rectify the insufficient boundary checks responsible for the issue. (sec.cloudapps.cisco.com)

Understanding the Patch:

The core of the vulnerability lies in how the web services interface processes specific HTTP requests. The software updates enhance the validation mechanisms for incoming HTTP requests, ensuring that data is properly checked before processing. This prevents the possibility of buffer overflow conditions that could lead to system reloads or denial of service (DoS) scenarios.

Implementing the Patch:

1. Identify Your Current Software Version:

   • Access your device's command-line interface (CLI).

   • Execute the following command to display the current software version:

     show version
     

   • Note the version number displayed.

2. Determine the Appropriate Fixed Release:

   • Refer to the Cisco Security Advisory to find the first fixed release corresponding to your current software version. (sec.cloudapps.cisco.com)

3. Download the Fixed Software:

   • Navigate to the Cisco Software Download Center.
   • Log in with your Cisco credentials.
   • Locate the fixed software release for your device model and current software version.
   • Download the appropriate software image.

4. Upgrade the Software:

   • Follow the standard upgrade procedures for your device:
     • Transfer the new software image to your device.
     • Verify the integrity of the image.
     • Set the device to boot from the new image.
     • Reload the device to complete the upgrade.

Post-Upgrade Verification:

After upgrading, it's crucial to verify that the device is operating with the updated software:

• Execute the show version command again to confirm the software version.
• Monitor the device logs to ensure there are no unexpected errors or issues.

By diligently applying this patch, you fortify your network infrastructure against potential exploits targeting this vulnerability, thereby maintaining the integrity and availability of your services.

Affected Systems and Versions

• Cisco Secure Firewall Adaptive Security Appliance (ASA) Software: specific affected versions are detailed in the Cisco Security Advisory
• Cisco Secure Firewall Threat Defense (FTD) Software: specific affected versions are detailed in the Cisco Security Advisory
• The vulnerability affects systems with the web services interface enabled. Refer to the advisory for exact version numbers and configurations.

Vendor Security History

Cisco has previously addressed similar buffer overflow and input validation vulnerabilities in its ASA and FTD product lines, including CVE-2016-1287 and other web services interface flaws. The vendor typically issues timely advisories and patches, but recurring memory safety issues highlight ongoing challenges in secure development for complex network appliances.

References

• NVD entry for CVE-2025-20263
• MITRE CVE entry
• Cisco Security Advisory