Pi3Web ISAPI DoS vulnerability
 
Discovered by: Hamid Ebadi
CSIRT Team Member
Amirkabir University CSIRT Laboratory (APA Laboratory)
 
autcert@aut.ac.ir
 
 
Introduction
Pi3Web is a free, multithreaded, highly configurable and extensible HTTP server and development environment for cross platform internet server development and deployment. Pi3web is vulnerable to a denial of service (DoS) vulnerability whenever an invalid ISAPI module is requested from server.
 
Vulnerable version
Pi3Web <=2.0.3
 
Vulnerability
By requesting the following URL from pi3web the server crashes:
http://WEB_SITE/isapi/users.txt
 
EnhPi3.exe -Bad Image
The application or DLL c:\Pi3Web\Isapi\users.txt is not a valid Windows image. Please check this against your installation diskette The vulnerability is caused.
 
The crash is due to insufficient checks for incoming requests. Whenever a file in ISAPI directory, which is not a valid DLL is requested, the server tries to load it into memory as a DLL library and a crash happens.
 
Workaround
Before an official patch is released, use one of the following workarounds to mitigate the problem:
 
1. Disable ISAPI mapping in server configuration in Server Admin > Mapping Tab.
2. Delete the users.txt, install.daf and readme.daf in ISAPI folder.
 
 
Credit
This vulnerability has been discovered by Hamid Ebadi from Amirkabir university CSIRT laboratory.
 
autcert@aut.ac.ir
https://www.ircert.cc

# milw0rm.com [2008-11-13]