IBM Lotus Domino Server Web Service DoS Vulnerability

iDEFENSE Security Advisory 04.06.05
http://www.idefense.com/application/poi/display?type=vulnerabilities
April 6, 2005

I. BACKGROUND

IBM Lotus Domino Server software provides messaging, calendaring and
scheduling capabilities on a variety of operating systems. More
information about the product is available from:

    http://www.lotus.com/products/product4.nsf/wdocs/dominohomepage

II. DESCRIPTION

Remote exploitation of a denial of service vulnerability in IBM Corp.'s
Lotus Domino Server web service allows attackers to crash the service,
thereby preventing legitimate access.

The problem specifically exists within the module NLSCCSTR.DLL. A
recursive call loop is made continually when parsing the following
example GET request:

    GET /cgi-bin/[xxx] HTTP/1.0
    Host: 10.10.0.100

Where [xxx] represents a long string (~330) of UNICODE decimal value 430
characters. The request triggers a stack exhaustion, which during
testing against Lotus Domino Server version 6.5.1 occurred at the
following instruction just prior to a call to NLSCCSTR.ucnv_toUnicode():

    6236B82B PUSH ECX

This results in the immediate crash of nHTTP.EXE and is not reported to
the NSERVER terminal. The crash occurs only when the long string is
prefixed with /cgi-bin/, as Lotus Domino Server uses two different
routines when handling requests made to the root directory and cgi-bin.
Examining the call stack at the time of crash reveals the issue. The
procedure NLSCCSTR.6236B080 is recursively called from the instruction
at address NLSCCSTR.6236B73D. A condition that is checked earlier would
JMP over this recursive call:

    PROCEDURE NLSCCSTR.6236B080 (Lotus Domino Server 6.5.1)
            ...
            6236B70D  TEST EAX, EAX
        +-< 6236B70F  JE SHORT NLSCCSTR.6236B77D
        |   ...
        |   6236B73D  CALL NLSCCSTR.6236B080
        |   ...
        +-> 6236B77D  MOV EAX, [EBP+20]

Further up the call stack we can find the following originating calls
with symbolic names:

    Procedure=NLSCCSTR.ccSTRCpyXlateExt
    Called from=NLSCCSTR.623DF3B8
    
    Procedure=nnotes.NLS_xlate_string32
    Called from=nnotes.60197A09

While portions of the stack are overwritten with attacker-supplied data,
gaining flow control to execute arbitrary code does not seem possible.

III. ANALYSIS

Exploitation of this vulnerability allows unauthenticated remote
attackers to crash the web service, thereby preventing legitimate usage.
This attack requires minimal resources to launch and can be repeated to
ensure that an unpatched computer is unable to recover. A successful
attack does not generate error messages in the NSERVER terminal.
However, the nHTTP.exe process has indeed crashed.

Restarting Domino Server will resume normal functionality.

IV. DETECTION
 iDEFENSE has confirmed the existence of this vulnerability in Lotus
Domino Server version 6.5.1. It has been reported that Lotus Domino
Server 6.03 is also vulnerable. It is suspected that earlier versions of
Lotus Domino Server are also affected. Additionally, iDEFENSE has
confirmed that Lotus Domino Server version 6.5.3 is not affected by this
issue.

V. WORKAROUND

Employ firewalls, access control lists or other TCP/UDP restriction
mechanisms to limit access to systems and services.

VI. VENDOR RESPONSE

IBM has released technote #1202446 for this issue. The vendor has been
unable to reproduce the issue and has therefore not released any
patches. iDEFENSE Labs testing has shown this product to be vulnerable
to the issue described in this report. Customers should consider
upgrading to Lotus Domino Server version 6.5.3, which iDEFENSE has
confirmed as being not vulnerable.

VII. CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not
been assigned yet.

VIII. DISCLOSURE TIMELINE

02/07/2005  Initial vendor notification
02/09/2005  Initial vendor response
04/06/2005  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.