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.


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