[Full-disclosure] Skype v. 5.x.x - information disclosure

[Osama Bin Error <oerror@xxxxxxxxx>]

Title:
======
Skype v. 5.x.x - information disclosure

Date:
=====
2012-02-13

Introduction:
=============
Skype is a proprietary voice-over-Internet Protocol service and
software application.

Abstract:
=========
We have discovered improper chat logs handling, which cause in logs
accessibility even if user had enabled "no history" option in "Keep
history for" settings or even destroy it manually with "Clear history"
button.

Report-Timeline:
================
2012-02-13:     Public Disclosure

Status:
========
Published

Exploitation-Technique:
=======================
Local

Severity:
=========
Low

Details:
========
As mentioned in the Skype FAQ
(https://support.skype.com/en-gb/faq/FA140/Managing-your-privacy-settings-Windows):
"You can choose how long to keep your conversation history for, or
delete it altogether.
1. To change your history settings, in Skype from the menu bar click
Skype > Privacy.
2. Below Keep history for, click on the drop-down list and select the
amount of time you would like your history to be saved for.
Choose from forever, 3 months, 1 month, 2 weeks or no history at all.
3. To delete your conversation history, click Clear history. This
removes your entire history, including instant messages, calls,
voicemails, text messages, sent and received files. If you delete your
conversation history, you cannot recover it."

This sounds safely, but in fact Skype stored all incoming and outgoing
chat messages into local sqlite3 DB (file main.db, table Messages), in
plain text. Even if "Keep history for"->"no history" option in
Settings->Security is enabled, Skype write all your data into Messages
table, but executes "delete * from Messages"  after program exit. This
command will destroy messages at logical level in DB, but in fact, in
physical level all messages data stay alive (blocks in the DB file
only marks as destroyed), and simply can be recovered even with text
editor (as mentioned above, it is stored in plain text).

Proof of Concept:
=================
In Windows XP, go to "C:\Documents and Settings\%user
name%\Application Data\Skype\%Skype user name%" and open file main.db
with text editor. All the ducks inside.

Credits:
========
Anonymous

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