Vulnerability Note VU#868219

Multiple vendors' HTTP content/virus scanners do not check data tunneled via HTTP CONNECT method

Overview

Multiple vendors' HTTP anti-virus and content filters do not inspect the contents of HTTP CONNECT method tunnels. As a result, viruses or other restricted HTTP content may not be blocked as specified by policy.

I. Description

Many anti-virus and content filter products that are designed to inspect HTTP application data rely on HTTP proxy functionality to examine the contents of HTTP connections. In turn, HTTP proxy services commonly support the HTTP CONNECT method, which is designed to create a TCP connection that bypasses the normal application layer functionality of the proxy. Typically, the HTTP CONNECT method is used to tunnel HTTPS connections through an HTTP proxy. The application layer data in an HTTP CONNECT method tunnel is opaque to the proxy service. The default configurations of many HTTP proxy services allow arbitrary TCP connections to be made using the HTTP CONNECT method [VU#150227].

As most HTTP proxy services ignore the HTTP data contained within an HTTP CONNECT method tunnel, so do most HTTP anti-virus and content scanners. As a result, it may be possible to create an HTTP CONNECT method tunnel through a vulnerable HTTP anti-virus or content scanner and transfer viruses or other restricted HTTP content.

II. Impact

A malicious actor may be able to bypass HTTP anti-virus software and HTTP content restrictions by transferring data via an HTTP CONNECT method tunnel.

III. Solution

Upgrade or Patch

Upgrade or apply a patch as specified by your vendor.

Architect HTTP Content Inspection

Depending on the behavior of different HTTP proxy and HTTP anti-virus/content inspection products, it may be possible to design a system that is able to inspect data that has passed through an HTTP CONNECT method tunnel.

Examine Tunneled Data

If possible, configure your HTTP anti-virus/content filters to examine the application layer contents of HTTP CONNECT method tunnels.

Use Desktop Anti-Virus Software

Deploy and maintain updated anti-virus software on client systems.

Systems Affected

Vendor	Status	Date Notified
F-Secure	Not Vulnerable	5-Jun-2002
F5 Networks	Not Vulnerable	28-May-2002
Hewlett-Packard Company	Not Vulnerable	29-May-2002
Sophos	Not Vulnerable	30-May-2002
Trend Micro	Vulnerable	15-Apr-2002

References

VU#150227
http://www.aerasec.de/security/index.html?lang=en&id=ae-200202-051
http://www.ietf.org/rfc/rfc2817.txt
http://www.web-cache.com/Writings/Internet-Drafts/draft-luotonen-web-proxy-tunneling-01.txt

Credit

The CERT/CC thanks Peter Bieringer and AERAsec Network Services and Security GmbH for information used in this document.

This document was written by Art Manion.

Other Information

Date Public:	2002-02-22
Date First Published:	2002-10-15
Date Last Updated:	2002-10-15
CERT Advisory:
CVE-ID(s):
NVD-ID(s):
US-CERT Technical Alerts:
Metric:	8.69
Document Revision:	18

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