Yahoo! Messenger may be storing all session data 'Unencoded' on the local machine
Title: Yahoo! Messenger May Be Storing All Session Data 'Unencoded' On The
Local Machine
Discovered By: Torseq Tech. <bindshell@xxxxxxxxx>
Date: Wednesday, May 18, 2005
Application affected: Yahoo! Messenger ver. 5.x - 6.0 (all builds) Windows,
*Nix/Mac ? (not tested)
Vendor: Yahoo! Inc.
Proof-of-Concept included: Yes
Fix Available: Yes (temporary)
Description: By activating the "Logfile" feature in Yahoo! Messenger a person
(perhaps unauthorized) is able to secretly log and view virtually all
communications sent and received by Yahoo! Messenger from all IDs logged into
Messenger on the local computer. Awareness of this logging is virtually none
unless this feature is exclusively known about beforehand by the users and they
know exactly where to look for the feature's presence (not likely). When using
this feature you may be susceptible to privacy breaches and increased risk for
potential remote DoS attacks to be launched successfully.
Summary:
A much lesser-known feature in Yahoo! Messenger is one called the "Logfile"
feature, which can be enabled/disabled remotely or locally through the YMSGR:
URL handler. If given physical access to a publicly "shared" system (or home)
it is possible to create a registry key and set the value enabling the feature
without having Messenger alert future users following the reg write of the
logging that's taking place. When Messenger is started up the entire login, all
chat room conversations, all PMs, conferences, chat invitations, add buddy
requests/successes/denies, and mobile text messages both in/out will be logged.
User's cookies, login challenge strings and challenge responses, user's buddy
lists, ignore lists, aliases on the accounts and personal status messages etc.
will all be stored in a text file on the local computer, all completely
unencrypted and in a readable (though ugly) raw packet dump of clear-text.
Presentation:
Unlike the 'recognized' and preference-accessible Yahoo! Messenger Archive
feature that allows for archiving of PMs, conferences, and mobile text messages
the Logfile feature isn't accessible from anywhere in Messenger other than
through invoking the YMSGR: handler with the correct arguments to
activate/deactivate it's functionality. This feature is also not very
documented (not documented officially), with the exception of 1 search result
on google with information about it from a third party (at the time of this
writing).
Unlike the Archiving feature which is enabled/disabled for each invidual user
on a per-ID basis, this Logfile feature, when enabled, causes Messenger to log
all communications both sent and received and append their contents in
clear-text to an existing text file called ypager.log. By default this text
file, in the same directory as Messenger, is used to log basic connection
successes and failures. When the Logfile feature is activated ypager.log then
becomes an entirely "different" file storing detailed log information above and
beyond it's normal troubleshooting statistics.
Several problems exist when this feature is activated. The first problem is
that you're able to make a manual registry write (which can be done even on
limited and guest accounts on XP) that when made, after being queried and found
by Messenger, is acted upon without alerting all future user(s) that logging
will take place on their IDs for all sessions thereafter. You can enable this
feature locally by making a registry write and creating the DWORD "Use Logfile"
with a value of '1', or disable by setting the value to '0' or deleting the
DWORD entirely from "HKEY_CURRENT_USER\Software\Yahoo\pager". When a manual reg
write is made it logs all user's data, it's scope isn't limited to individual
IDs but any IDs used in Messenger on the computer at any time.
This feature can be enabled remotely using the YMSGR: handler link
YMSGR:enablelog?1 and clicking on "enable" through an IFRAME or in a hyperlink
in pm or chat. The feature can be disabled remotely using YMSGR:enablelog? and
clicking on "disable" to stop the logging after shutting down Messenger and
restarting it. When logging is enabled through the use of the YMSGR: handler
the current user is prompted from the enable/disable Warning dialog box but the
message does not cearly indicate exactly what will be logged, where it will be
stored, who will be logged or whether or not the data will be encoded or not
when stored. A user could be tricked into enabling this feature remotely, and
quite easily, without knowing what it does or how it works, much less how to
turn it off if they needed to for performance or privacy reasons.
Since many businesses communicate using Yahoo! Messenger employees and/or even
outsiders could keep track of business conferences that took place, chat room
conversations and private messages (PMs) that might have taken place during
workdays. Colleges with Yahoo! Messenger installed on their campus computers
could be used to harvest all conversational data as well as private data
(cookies, buddylists and ignore lists) from students using it between classes.
Comparing and contrasting the known Yahoo! Archive feature against this
"Logfile" feature to indicate the differences is as follows:
Yahoo! Messenger Archive feature:
- Is Messenger GUI-accessible through preferences for enabling and disabling.
- Selective logging exists for PMs, conferences and/or mobile text messages and
alerts.
- Logged data is stored on the local computer in the form of .dat files of
which the contents are XORd (though very minimal) with the user ID to prevent
your typical local user from viewing the contents. Ability to view the contents
of the logfiles is granted when signed into the account on which the logs were
created (where the user ID and password would be needed to read them).
- Is enabled and disabled on a per-ID basis, meaning each ID logged into
Messenger can choose whether to enable archiving or not (default is disabled
for all).
- PMs received from senders that are not replied back to during the session are
not archived.
Yahoo! Messenger Logfile feature:
- Is not Messenger GUI-accessible from anywhere for simple enabling and
disabling.
- No selective logging exists per service type, virtually everything that can
be sent or received through Messenger is logged (much broader scope of logged
activity vs. Archiving).
- Logged data is stored on the local computer in the ypager.log text file of
which the contents are not encoded at all to prevent onlookers from viewing the
contents.
- Is enabled and disabled on a "global" basis, meaning once enabled the logging
takes place for all communications on all IDs logged into and used in Messenger.
- Received PMs and all communications from senders that are not replied back to
during the session are still logged in the text file (unlike Archiving's
behavior).
Potential remote DoS vulnerability:
If in a highly 'active' chat room environment, PM or conference where there's
multiple lines of text being sent back and forth at high rates there's the
possibility that this log could get quite huge due to the actual packet-like
structure being used for the logging and the additional details about each
packet's contents being appended. This text file could grow into megabytes if
enough elapsed time and activity has taken place. A Denial-of-Service condition
could possibly be made if logging was activated and the attacker was able to
force large amounts of PM or chat room data to the target's Messenger client
forcing it to spend a lot of resources and time logging all of the data flood's
contents to the text file, possibly resulting in a client crash or decreased
system performance. This scenario would be all too real as PM bombing and
various other sorts of flooding (booting) exist practically everywhere on
Yahoo! Chat.
Logfile Analysis:
Recv 5/18 0:47:45| type=6, status=1,
data=5torseq_tech4my_name_is_tr0nix244278527252PpuInhgAiRFwuCJpNC4=97114Hello
there sir63;0640, len=121
The line above from ypager.log is an ASCII packet dump that indicates that a PM
was received on the ID "torseq_tech" from the ID "my_name_is_tr0nix"
timestamped with the date and time of receipt. The message here is "Hello there
sir". The YMSG header status= field value is also provided as well as the YMSG
service type being "6" in decimal (Private Message). The YMSG payload length,
being 121 Bytes (derived from the YMSG 20 Byte header subtracted from the
payload continuation) is also present telling us exactly how large the messages
received were in octets. Due to the rawness of the structure from the dump a
parser could be written to parse the type= value, status= value, data= and len=
values along with the direction (Sent & Recv) and the timestamp to be displayed
with better human-readability when viewing the log's contents as a whole. The
miscellaneous letters and numbers within the data= field could also be stripped
out if each service type's delimiters (being those numb
ers and letters) were extracted from the actual viewable message text.
Reconstructing whole chat room conversations, PM conversations, conferences and
harvesting buddy lists, ignore lists and cookies etc. could all be accomplished
for multiple IDs used from the computer's Messenger client.
Proof-of-Concept:
To manually activate the Logfile feature without prompting the user upon it's
activation (physical access normally required) go here:
http://geocities.com/ken_thompson39/log/Use_Logfile.html
To trick users into activating this feature remotely you could have them visit
a web page (like this one) or have them click on a hyperlink with the handler
embedded. When they see the "Do you want to enable logging on Yahoo!
Messenger?" Warning dialog box popup you could inform them that this just
activates the Yahoo! Messenger Archive feature for them or something similar to
get them to do it.
http://geocities.com/ken_thompson39/log/Logfile.html
Consequences:
Possible data theft by local users of the computer, compromised IDs and friends
list communications (through cookie logins from the IDs and cookies gathered)
via impersonation and increased risk for potential remote DoS attacks to be
launched successfully due to such heavy loads of logging that can be induced.
Solution (temporary):
Set ypager.log permissions to Read-only or check for the logging when Messenger
is started up each time it's used from a shared computer using the URL handler
to disable it when signing in. Deleting the file before Messenger is started
won't help as the file is recreated (it's needed even if the Logfile feature is
disabled) if it isn't found in the Messenger folder.