Anon Proxy Server <= 0.102 remote buffer overflow

[L4teral <l4teral () gmail com>]

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Anon Proxy Server <= 0.102 remote buffer overflow
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Author:          L4teral <l4teral [4t] gmail com>
Impact:          remote buffer overflow
Status:          patch available


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Affected software description:
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Application:     Anon Proxy Server
Version:         <= 0.102
Vendor:          http://anonproxyserver.sourceforge.net

Description:
A fast http, https, socks caching proxy server.
Easy web based configuration, optional p2p anonymous mode.


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Vulnerability:
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When user authentication is enabled, the server can be exploited by
passing a long username containing quotes. The username is checked
for length, but the function strquotecpy() in the file access.c
escapes quote characters by prepending a backslash, enlarging
the string without checking it for the resulting length.


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PoC/Exploit:
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Use the following perl code to generate a username triggering
the buffer overflow when used for authentication:

#!/usr/bin/perl
print "A" x 430 . '"' x 29 . "A" x 40 . "\n";

The program will catch the exception and restart itself - attach a
debugger to see the EIP overwrite.


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Solution:
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Upgrade to version 0.103 or higher.


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Timeline:
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2008-01-27 - vendor informed
2008-01-28 - vendor released patch
2008-02-03 - public disclosure