Date: Wed, 10 May 2000 14:50:18 -0500 From: Jim Early <earlyjp@CS.PURDUE.EDU> Subject: Gnapster Vulnerability Compromises User-readable Files To: BUGTRAQ@SECURITYFOCUS.COM Gnapster Vulnerability Compromises User-readable Files This vulnerability was discovered at the Center for Education and Research in Information Assurance and Security (CERIAS) at Purdue University <http://www.cerias.purdue.edu> by: Tom Daniels <email@example.com> Florian Buchholz <firstname.lastname@example.org> James Early <email@example.com> Environment: Intel PII-based System Linux RedHat Version 6.2 (may apply to all OS's running Gnapster) Gnapster Version 1.3.8 (and earlier) Gnapster is an open source, independent implementation of the Napster protocol client. Problem: It is possible for anyone to obtain any user-readable file by sending a properly formed "GET" command that contains the full path of the file. This vulnerability exists because Gnapster fails to check that the requested file is an explicitly shared MP3 file before providing it. Note: This is the same vulnerability described in FreeBSD-SA-00:18 Anyone running Gnapster version 1.3.8 or earlier is vulnerable. Given the IP address and TCP port of a vulnerable client, an attacker can send a request for an arbitrary file to the Gnapster client. If the user has read access to the file, the client will then respond with the contents of the file. Solution: We contacted the program's author, and he promptly created a new version which addresses this vulnerability. The fix simply checks that a requested file is in the list of shared files. The current version can be downloaded from: http://download.sourceforge.net/gnapster/gnapster-1.3.9.tar.gz Exploit: We have developed an exploit code for this vulnerability, but we will not be releasing it to the public. Conclusion: We have described a vulnerability in one client implementation of the Napster protocol. There may be similar problems in other implementations of the protocol as we have not done an exhaustive search. The official Windows client does not seem to be affected. We urge users to upgrade to the latest version of Gnapster.