QDAV-2001-7-3

`Interactive Story File Disclosure Vulnerability  
qDefense Advisory Number QDAV-2001-7-3  
  
Product: Interactive Story  
  
Vendor: Valerie Mates (http://www.valeriemates.com)  
  
Severity: Remote; Attacker may read arbitrary file  
  
Versions Affected: Version 1.3  
  
Vendor Status: Vendor contacted; has released new version, 1.4, which is   
not vulnerable  
  
Cause: Failure to validate input  
  
In Short: Interactive Story does not properly validate the contents of a   
hidden field entitled "next". By setting that field to the name of a file,   
and using double dots and poison nulls, an attacker can cause Interactive   
Story to display the contents of any file.  
  
  
The current version of this document is available at   
http://qDefense.com/Advisories/QDAV-2001-7-3.html.  
  
Details:  
Interactive Story contains the following lines:  
  
$nextfile = "$story_dir/$in{'next'}.txt";  
...  
elsif ((-e $nextfile) && ($in{'submit'} eq "")) {  
...  
  
while (<STORY>) {  
print $_;  
}  
...  
}  
  
If an attacker sets the "next" field to something like   
../../../../../../../../../../etc/passwd%00, Interactive Story will open   
and display the password file. This technique can be used to display any   
file that the web server has permission to read.  
Solution:  
  
Valerie Mates has released an upgrade, version 1.4, which strips special   
characters from the "next" field.  
  
  
  
  
© 2001 qDefense Information Security Consultants. qDefense is a subsidiary   
of Computer Modeling Corp.  
This document may be reproduced, in whole or in part, provided that no   
modifications are made and that proper credit is given. Additionally, if it   
is made available through hypertext, it must be accompanied by a link to   
the qDefense web site, http://qdefense.com.  
qDefense Advisories  
[email protected]  
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`