CVE-2021-1444 - Cross-Site Scripting Vulnerability in Cisco ASA and FTD Web Interfaces

In October 2021, Cisco published an advisory for a serious vulnerability: CVE-2021-1444. This security flaw affects the web services interface of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software. If your organization uses either of these devices and exposes their web interfaces, you need to understand this vulnerability and take action right away.

What Is CVE-2021-1444?

CVE-2021-1444 is a cross-site scripting (XSS) vulnerability. This kind of bug lets attackers inject harmful scripts into web pages viewed by other users. This specific issue in Cisco's software is due to insufficient validation of user-supplied input by the web interface.

In simple terms: the device’s web interface doesn’t clean up user input like it should. An attacker can sneak in malicious code, and if an administrator or user clicks a bad link, the attacker’s code can run in the browser.

Craft a Malicious Link

The attacker creates a web link that, when opened, injects their script into the Cisco web interface.

Trick a User

The attacker convinces a user (typically an administrator) to click the link. This might be via email, chat, or a malicious website.

Script Executes

When the link is clicked, the script runs inside the victim’s browser – but in the security context of the Cisco web interface. This lets the attacker do almost anything the user could do:

Proof-of-Concept (PoC) Exploit Example

Below is a simple example of how such a crafted link might look. Let’s say your device’s web interface is at https://asa.example.com/admin:

<!-- Malicious Link Example -->
<a href="https://asa.example.com/admin?username=%22%3E%3Cscript%3Ealert('XSSed!')%3C/script%3E">Click here</a>

What’s going on?

The link injects a script tag into the “username” field.

- If the web interface displays this username directly in the page without cleaning it up, the alert will pop up, showing the attack works.

A real attacker would use a more subtle payload to steal data.

Note: DO NOT use this against live systems without permission. This example is for educational purposes only!

Cisco Firepower Threat Defense (FTD) Software

Attack surface is ANY web front end where a user or admin might log in.

Updates Are Available

Cisco released patched versions for all affected products.
THERE ARE NO WORKAROUNDS. The only solution is to patch.

Visit the Cisco Security Advisory:

CVE-2021-1444 Official Advisory

Download and apply the correct firmware update for your device.

Advisory Note:
This CVE is part of the October 2021 Cisco ASA, FTD, and FMC Security Advisory Bundled publication.
See the full list of advisories here (official Cisco listing).

More References

- Cisco Security Advisory: cisco-sa-asaftd-xss-RD92bRnT
- National Vulnerability Database Entry
- OWASP XSS Guide

Final Thoughts

CVE-2021-1444 is a dangerous bug in widely-used Cisco security products. Since there’s no workaround, patching is your only option. Don't delay!

If you manage Cisco ASA or FTD, check your software version and upgrade immediately to keep your organization safe.

Timeline

Published on: 11/18/2024 15:31:08 UTC