adb (Android Debug Bridge) backup/restore allows you to backup and restore
applications via adb, including system applications.
The backed up files are stored in tar.zlib (named .ab by default) files.
"adb restore" is vulnerable to a directory traversal attack. By creating a
file named "apps/com.andoird.settings/db/../../../local.prop" inside the
backup file, the restore operation would restore the file onto
/data/local.prop (rather than
/apps/apps/com.android.settings/databases/...).
The "apps","com.android.setttings" and "db" directory names are extracted
for determining the package name and the directory (db=>database) to
restore the relevant file onto, and everything that
follows is expected to be the filename.
This vulnerability is not specific to com.android.settings (demonstrated
below), but rather any system application that support backup and restore.
One can use this vulnerability for escalating privileges to root on Android
phones supporting adb backup/restore (for example) as follows:
# tested on HTC phone with android 4.0.4. This will likely work on other
configurations as well with some modifications.
# backup your settings app, before we overwrite its files.
adb backup -f settings.ab com.android.settings
(select approve to begin backup)
# restore the malformed backup file, which will create /data/local.prop
(with ro.kernel.qemu=1) -- attached to this email.
adb restore special.ab
# restart the phone.
adb shell
# adb should now run as root.
# install SU, or create a setuid root shell somewhere.
# delete /data/local.prop
# the malformed backup file will likely break you settings app, so expect
some oddities until it's all restored.
adb restore settings.app
Bin4ry and later Saurik had used a race condition in "adb restore" (
http://forum.xda-developers.com/showthread.php?t=1886460) to gain root,
while this attack also uses adb restore, it uses a different attack vector,
and does not involve any race conditions.
Thanks,
Ariel.
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