Vulnerability Report For Microsoft PhoneBook Server Overflow

Advisory ID Internal

Bugtraq ID: 2048

CVE Name: CVE-2000-1089

Title: Microsoft PhoneBook Server buffer overflow

Class: Boundary condition error

Remotely Exploitable: Yes

Locally Exploitable: Yes


Vulnerability Description:

The Phone Book Service is an optional component that ships with the NT 4 Option Pack and Windows 2000.

It is not installed by default.

A buffer overflow vulnerability was discovered in the URL processing routines of the Phone Book Service requests on IIS 4 and IIS 5.

If exploited, this vulnerability allows an attacker to execute arbitrary code and obtain a remote command shell with those privileges of the IUSR_machinename account (IIS 4) or the IWAM_machinename account (IIS 5).


Vulnerable Packages/Systems:

Microsoft Windows NT 4.0
Microsoft Windows NT 4.0 Enterprise Server Edition
Microsoft Windows 2000 Server
Microsoft Windows 2000 Advanced Server


Solution/Vendor Information/Workaround:

Microsoft has released a fix that eliminates the vulnerability.

It can be obtained from:

Microsoft Windows NT 4.0:

Microsoft Windows 2000:

NOTE: The NT 4.0 fix can be applied to systems running NT 4.0 Service Pack 6a. This fix will be included in NT 4.0 Service Pack 7. The Windows 2000 fix can be applied to Windows 2000 Gold or Service Pack 1.

This fix will be included in Windows 2000 Service Pack 2.

Note Additional security patches are available at the Microsoft Download Center.

More Information
Frequently Asked Questions: Microsoft Security Bulletin MS00-094,
Microsoft Knowledge Base article Q276575 discusses this issue and will be available soon.

Microsoft TechNet Security web site,

Vendor notified on: September 27th, 2000



This vulnerability was discovered by Alberto Soliño of CORE SDI, Buenos Aires, Argentina.

It was also discovered and reported independently at the same time by David Litchfield from @Stake Inc.

We would like to thank the Microsoft Security Response Team for their quick acknowledge to the report and the prompt response and efforts generating a fix.

This advisory was drafted with the help of the

Vulnerability Help Team. For more information or assistance drafting advisories please mail [email protected].

Technical Description - Exploit/Concept Code:

The Phone Book server services requests using the Internet Information Services 5.0 with URIs such as http://hostname/pbserver/

According to Microsoft's documentation a DLL (PBSERVER.DLL) is exported and the services can be used making requests with the following format:


ver=&pb=<STRING=db name>

NOTE: The above URL might be wrapped

In the DLL checks the total length to ensure that request does not exceed 1024 bytes, however it is possible to overflow a local variable of fixed length in the DLL by sending a request with the following form:

GET /pbserver/pbserver.dll?&&&&&&pb=AAAAAA... (less than 980 chars)

The result is an exception reported in the Event log with source WAM like the following:
The HTTP server encountered an unhanded exception while processing the
ISAPI Application '
+ 0x41414143
+ 0x41414139
pbserver!HttpExtensionProc + 0x1C
wam!DllGetClassObject + 0x808
RPCRT4!NdrServerInitialize + 0x4DB
RPCRT4!NdrStubCall2 + 0x586
RPCRT4!CStdStubBuffer_Invoke + 0xC1
ole32!StgGetIFillLockBytesOnFile + 0x116EC
ole32!StgGetIFillLockBytesOnFile + 0x12415
ole32!DcomChannelSetHResult + 0xDF0
ole32!DcomChannelSetHResult + 0xD35
ole32!StgGetIFillLockBytesOnFile + 0x122AD
ole32!StgGetIFillLockBytesOnFile + 0x1210A
ole32!StgGetIFillLockBytesOnFile + 0x11E22
RPCRT4!NdrServerInitialize + 0x745
RPCRT4!NdrServerInitialize + 0x652
RPCRT4!NdrServerInitialize + 0x578
RPCRT4!RpcSmDestroyClientContext + 0x9E
RPCRT4!NdrConformantArrayFree + 0x8A5
RPCRT4!NdrConformantArrayFree + 0x3FC
RPCRT4!RpcBindingSetOption + 0x395
RPCRT4!RpcBindingSetOption + 0x18E
RPCRT4!RpcBindingSetOption + 0x4F8
KERNEL32!CreateFileA + 0x11B

For additional information specific to this message please visit the Microsoft Online Support site located at:
By sending a carefully crafted HTTP request an attacker can bypass the total length check and overflow a local variable in PBSERVER.DLL allowing the execution of arbitrary code with the privileges of the IUSR_machinename account (IIS 4) or the IWAM_machinename account (IIS 5) on the vulnerable systems.

Copyright notice
The contents of this advisory are copyright (c) 2000 CORE SDI Inc. and may be distributed freely provided that no fee is charged for this distribution and proper credit is given.