RedTeam Pentesting GmbH

Skyhigh Security Secure Web Gateway: Cross-Site Scripting in Single Sign-On Plugin

RedTeam Pentesting identified a vulnerability which allows attackers to craft URLs to any third-party website that result in arbitrary content to be injected into the response when accessed through the Secure Web Gateway. While it is possible to inject arbitrary content types, the primary risk arises from JavaScript code allowing for cross-site scripting.

Details

Product: Secure Web Gateway
Affected Versions: 10.2.11, potentially other versions
Fixed Versions: 10.2.17, 11.2.6, 12.0.1
Vulnerability Type: Cross-Site Scripting
Security Risk: high
Vendor URL: https://www.skyhighsecurity.com/en-us/products/secure-web-gateway.html
Vendor Status: fixed version released
Advisory URL: https://www.redteam-pentesting.de/advisories/rt-sa-2022-002
Advisory Status: published
CVE: CVE-2023-0214
CVE URL: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-0214

Introduction

“Skyhigh Security Secure Web Gateway (SWG) is the intelligent, cloud-native web security solution that connects and secures your workforce from malicious websites and cloud apps—from anywhere, any application, and any device.”

(from the vendor’s homepage)

More Details

The Secure Web Gateway’s (SWG) block page, which is displayed when a request or response is blocked by a rule, can contain static files such as images, stylesheets or JavaScript code. These files are embedded using special URL paths. Consider the following excerpt of a block page:

<html>
<!-- FileName: index.html
     Language: [en]
-->
<!--Head-->
<head>
  <meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
  <meta http-equiv="X-UA-Compatible" content="IE=7" />
  <title>McAfee Web Gateway - Notification</title>
  <script src="/mwg-internal/de5fs23hu73ds/files/javascript/sw.js" type="text/javascript" ></script>
  <link rel="stylesheet" href="/mwg-internal/de5fs23hu73ds/files/default/stylesheet.css" />
</head>

Static content is loaded from URL paths prefixed with “/mwg-internal/de5fs23hu73ds/”. It was discovered that paths with this prefix are intercepted and directly handled by the SWG no matter on which domain they are accessed. While the prefix can be configured in the SWG, attackers can also obtain it using the vulnerability described in rt-sa-2022-001.

By reverse engineering the file “libSsos.so” and analysing JavaScript code, it was possible to derive the API of the “Ssos” plugin’s “SetLoginToken” action. Through the following call using the command-line HTTP client curl, the behaviour of the plugin was further analysed:

$ curl --proxy http://192.168.1.1:8080 -i 'https://gateway.example.com/mwg-internal/de5fs23hu73ds/plugin?target=Ssos&action=SetLoginToken&v=v&c=c&p=p'
HTTP/1.0 200 OK
P3P: p
Connection: Keep-Alive
Set-Cookie: MwgSso=v; Path=/; Max-Age=240;
Content-Type: application/javascript
Content-Length: 2
X-Frame-Options: deny

c;

The response embeds the values of the three URL parameters “v”, “c” and “p”. The value for “p” is embedded as value of the “P3P” header, the value of “c” as the response body and the value of “v” as the value of the cookie “MwgSso”.

It is also possible to include newline or carriage return characters in the parameter value which are not encoded in the output. Consequently, if the value of the parameter “p” contains a line break, arbitrary headers can be injected. If two line breaks follow, an arbitrary body can be injected. If a suitable “Content-Length” header is injected, the remaining headers and body of the original response will be ignored by the browser. This means that apart from the initial “P3P” header, an arbitrary response can be generated. For example, a page containing JavaScript code could be returned, resulting in a cross-site scripting attack.

Consequently, attackers can construct URL paths that can be appended to any domain and cause an arbitrary response to be returned if the URL is accessed through the SWG. This could be exploited by distributing such URLs or even by offering a website which performs an automatic redirect to any other website using such a URL. As a result, the SWG exposes its users to self-induced cross-site scripting vulnerabilities in any website.

Proof of Concept

In the following request, the “p” parameter is used to inject suitable “Content-Type” and “Content-Length” headers, as well as an arbitrary HTML response body.

$ curl --proxy http://192.168.1.1:8080 -i 'https://gateway.example.com/mwg-internal/de5fs23hu73ds/plugin?target=Ssos&action=SetLoginToken&v=v&c=c&p=p%0aContent-Type: text/html%0aContent-Length: 27%0a%0a<h1>RedTeam Pentesting</h1>'
HTTP/1.0 200 OK
P3P: p
Content-Type: text/html
Content-Length: 27

<h1>RedTeam Pentesting</h1>

As mentioned above, the HTTP response body could also include JavaScript code designed to interact with the domain specified in the URL resulting in a cross-site scripting vulnerability.

Workaround

None.

Fix

According to the vendor, the vulnerability is mitigated in versions 10.2.17, 11.2.6 and 12.0.1 of the Secure Web Gateway. This was not verified by RedTeam Pentesting GmbH. The vendor’s security bulletin can be found at the following URL:

https://kcm.trellix.com/corporate/index?page=content&id=SB10393

Security Risk

The vulnerability could be used to perform cross-site scripting attacks against users of the SWG in context of any domain. Attackers only need to convince users to open a prepared URL or visit an attacker’s website that could perform an automatic redirect to an exploit URL. This exposes any website visited through the SWG to the various risks and consequences of a cross-site scripting vulnerability such as account takeover. As a result, this vulnerability poses a high risk.

Timeline

2022-07-29 Vulnerability identified
2022-10-20 Customer approved disclosure to vendor
2022-10-20 Vulnerability was disclosed to the vendor
2023-01-17 Patch released by vendor for versions 10.2.17, 11.2.6 and 12.0.1.
2023-01-26 Detailed advisory released by RedTeam Pentesting GmbH

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