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CERT Coordination Center

Multiple intrusion detection systems may be circumvented via %u encoding

Vulnerability Note VU#548515

Original Release Date: 2001-09-07 | Last Revised: 2003-10-30

Overview

Multiple intrusion detection systems may be circumvented via %u encoding allowing intruders to launch attacks undetected.

Description

Most intrusion detection systems are capable of decoding URLs that are encoded using either the "UTF" or "hex-encode" encoding schemes. Microsoft's Information Server (IIS) employs both of these encoding schemes. It also makes use of an encoding scheme known as "%u encoding". According to the eEye Digital Security Advisory, "The purpose of this %u encoding seems to be for the ability to represent true Unicode/wide character strings." Because "%u encoding does not appear to be widely utilized by products other than Microsoft's Information Server (IIS), certain intrusion detection systems are not able to properly decode %u encoded requests.

Impact

An intruder can pass %u encoded malicious traffic undetected through an intrusion detection system in violation of implied security policies. This will typically be reconnaissance traffic and/or attack traffic directed at an IIS web server.

Solution

Contact your vendor for patches.

Vendor Information

548515
 
Affected   Unknown   Unaffected

Cisco Systems Inc.

Updated:  September 07, 2001

Status

  Vulnerable

Vendor Statement

Please see http://www.cisco.com/warp/public/707/cisco-intrusion-detection-obfuscation-vuln-pub.shtml

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

Enterasys Networks

Updated:  September 07, 2001

Status

  Vulnerable

Vendor Statement

Dragon Sensor 4.x was affected. Signatures to detect the new IIS UNICODE encoding flaw have been available, and a modification to the Web processing engine is already included in Dragon Sensor 5.0. To obtain dragon products, visit http://dragon.enterasys.com.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

Internet Security Systems Inc.

Updated:  September 07, 2001

Status

  Vulnerable

Vendor Statement

ISS X-Force has included a patch for this vulnerability in RealSecure Network Sensor X-Press Update 3.2. ISS X-Force recommends that all RealSecure customers download and install the update immediately. RealSecure X-Press Update 3.2 is now available. RealSecure Network Sensor customers can download XPU 3.2 from the following address: http://www.iss.net/db_data/xpu/RS.php
RealSecure Server Sensor version 6.0.1 includes a fix for this vulnerability. RealSecure Server Sensor 6.0.1 will be available for download on September 4, 2001. ISS X-Force recommends that all RealSecure customers upgrade their Windows Server Sensors to version 6.0.1. A patch is being developed for RealSecure Server Sensor 5.5 and will be available on or before August 31, 2001 at the ISS Download Center:
http://www.iss.net/eval/eval.php.

BlackICE products are not affected by this vulnerability. Attempts to exploit this vulnerability will trigger the “HTTP URL bad hex code” signature. The next BlackICE product update will specifically address “%u” encoding."

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.

The Snort Project

Updated:  September 18, 2002

Status

  Vulnerable

Vendor Statement

Snort 1.8.1 fixes this encoding bug. You can receive it from http://snort.sourcefire.com/.

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.

Addendum

The CERT/CC has no additional comments at this time.

If you have feedback, comments, or additional information about this vulnerability, please send us email.


CVSS Metrics

Group Score Vector
Base N/A N/A
Temporal N/A N/A
Environmental N/A

References

Acknowledgements

The CERT Coordination Center thanks eEye Digital Security for their advisory, on which this document is based.

This document was written by Ian A. Finlay.

Other Information

CVE IDs: CVE-2001-0669
Severity Metric: 13.13
Date Public: 2001-09-05
Date First Published: 2001-09-07
Date Last Updated: 2003-10-30 21:26 UTC
Document Revision: 47

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