[Full-Disclosure] Opera Skinned : Arbitrary File Dropping And Execution (Advisory)

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To: full-disclosure@lists.netsys.com
Date: Wed, 12 Nov 2003 02:18:34 -0800 (PST)

Opera Skinned : Arbitrary File Dropping And Execution
======================================================

I ABSTRACT:

Like other browsers, Opera Web Browser supports many
standard MIME types and also a few

Opera-specific MIME types. Of the Opera-specific
types, the implementation of the various browser

skin and browser configuration MIME types(listed
below) has a design flaw that allows the remote

dropping of an arbitrary file with an arbitrary name
and type in a known location. This is

triggered when the victim accesses a URL.

Exploitation becomes easier when this vulnerability is
combined with the other "Directory

Traversal" vulnerability described in the attached
advisory.

II VERSIONS AFFECTED:

All versions upto and including 7.21 that support the
flawed MIME types are vulnerable. Version

7.22 contains the fix.

III. IMPACT:

By using this flaw, an attacker may:

i. Drop arbitrary files with arbitrary names on a
victim's hard disk.
ii. Run scripts with higher privileges.
iii. Read the contents of the directories on a
victim's hard disk.
iv. Read any file.
v. Read M2 emails (Built-in Opera mail client).

IV. TECHNICAL DETAILS:

We will consider the "application/x-opera-skin" MIME
type first for the sake of clarity. The

issues are the same for the other five flawed MIME
types. Their specifics are mentioned in a

later section below.

1. Skinning Opera with "application/x-opera-skin":

According to the functionality that Opera provides, a
user can install a new skin just by

clicking on a link. Opera automatically downloads and
applies the skin without confirmation from

the user. For this to work, the MIME type of the skin
file has to be set to

"application/x-opera-skin" on the web server. The file
type of an Opera skin file is "*.zip". The

Opera skin file specification [2] says-

8<---------

"An Opera 7 skin file is a zipped file with extension
.zip that contains a "skin.ini" file at

root level and a bunch of images making up the skin.
The "skin.ini" file contains the whole skin
specification. All other files in the zip file are

pointed to by the specification in "skin.ini"." [2]

8<----------

Skins files are downloaded to "C:\Program
Files\Opera7\profile\Skin\<filename.ext>" (if the

install directory is "C:\Program Files\Opera7\". It is
*not* necessary for a remote attacker to

know the install path of Opera for exploitation.)

Skin files that do not have "*.zip" extensions but are
valid skin files are automatically

downloaded and applied by Opera if the correct MIME is
set on the httpd. They are downloaded to

the default skin file folder. However, these skins are
not shown in the "file>preferences>skin"

menu. Only skins with "*.zip" ext., are shown in the
list.

The security problem here is that even invalid,
corrupt skin files with any extension (including

exe,com, et al) are downloaded to the default skin
file location. The victim doesn't necessarily

have to know that he is downloading a skin. He just
clicks a malicious link and he is given a

harmless looking dialog box prompt saying that the
skin file is incompatible with the current

version of Opera *after the file is downloaded*. User
may click "OK" or "CANCEL" but it has no

effect on the download behaviour. The file is still
present in the skin file folder and it is not

deleted.

This means that an attacker can comfortably drop an
arbitrary file with an arbitrary name & type

on a victims hard disk in a known location by making
him access a simple, not-specially crafted

URL. Using an exploitation method detailed elsewhere,
the arbitrary file can be executed.

For instance, if a victim clicks on a link
http://foo.com/foobar.exe where the MIME type of

foobar.exe is set as "application/x-opera-skin",
foobar.exe is downloaded automatically to the

skin file folder. The name foobar.exe is preserved.
So, for a default install of Opera, the file

is dropped in and as "C:\Program
Files\Opera7\profile\Skin\foobar.exe".

2. Other flawed MIME types:

Other than the folder location where the file will be
dropped and the file type associated with

the MIME type, all the details are the same as the
skin MIME detailed above for the MIME types

listed below. The file type associated with a MIME
type does not hinder the dropping of files of

other types as shown above. It is just presented here
as useful information.

For all the MIME types below, the locations for a
default install are given. However, a default

install is not necessary for exploitation.

i."application/x-opera-skin" - Detailed above

ii."application/x-opera-configuration-skin" - File is
dropped in C:\Program

Files\Opera7\profile\skin.

iii."application/x-opera-configuration-keyboard" -
File is dropped in C:\Program

Files\Opera7\profile\keyboard. The file type
associated is "*.ini".

iv."application/x-opera-configuration-mouse" - File is
dropped in C:\Program

Files\Opera7\profile\mouse. The file type associated
is "*.ini".

v."application/x-opera-configuration-menu" - File is
dropped in C:\Program

Files\Opera7\profile\menu. The file type associated is
"*.ini".

vi."application/x-opera-configuration-toolbar - File
is dropped in C:\Program

Files\Opera7\profile\toolbar. The file type associated
is "*.ini".

About these MIME types, Opera's documentation says-

8<------------

"If the server returns content-type
"application/x-opera-configuration-menu" or

"application/x-opera-configuration-keyboard" or
"application/x-opera-configuration-mouse" and the

file has the "ini" extension, Opera will download and
install the menu, keyboard or mouse

gestures setup directly" [3]

8<------------

IV EXPLOITATION SCENARIOS & EXPLOIT:

According to my investigation, files can only be
dropped in the default folders mentioned above.

Using directory traversal techniques to drop the file
in other locations does not seem to be

feasible.

Although any file can be dropped on a victim's
computer, the highest compromise that can be

accomplished seems to be the running of scripts with
higher privileges. Files other than the file

types handled by Opera cannot be executed. This means
file types like exe, bat, etc., cannot be

executed although they may be dropped and file types
like html, txt, gif, etc., can be executed.

Nevertheless, the executable files dropped using this
vulnerability can be executed by using

other vulnerabilities(possibly in other software).

This flaw can be exploited alone but, if Opera is not
installed in the default path, a 'blind'

exploit will not work. Nevertheless, when this flaw is
combined with the Directory Traversal

vulnerability (detailed in the advisory "Opera Web
Browser Directory Traversal in Internal URI

Protocol" published by me, attached to this one),
'blind' exploitation, i.e., exploitation

without knowledge of the install path becomes
possible.

A proof of concept exploit is attached with this
advisory.

V. VENDOR RESPONSE & SOLUTION:

The vendor, Opera Software, deserves special mention
here. I had previously read about Opera

Soft's promptness in resolving security
vulnerabilities in their products. My experience with

them is one of the best I ever had with any vendor. I
hope they continue to maintain their good

record even with future security issues.

An updated version with a fix (7.22) is available from
the site - http://www.opera.com/download/

VI. CREDIT:

S.G.Masood (sgmasood@yahoo.com)

Hyderabad,
India.

VII. DISCLAIMER:

This advisory is meant only for the dissemination of
information, alerting the general public

about a security issue. Use this information at your
own discretion.

In brief, the author is not responsible for any use,
misuse, abuse of this information. Also,

this information is provided "as is" without any
warranty of any kind.

*PHEW*

EOF

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