The ZTE Score M phone, apparently available via Metro PCS in the US, comes with a special suid backdoor. The backdoor for a change does not use a fixed "secret" root password. But instead, the suid binary "sync_agent" has to be called with a special parameter.

If you do have an Android phone, take a look if you have this application in "/system/bin". At this point, only this one particular model is reported to have this application present, but it would be odd to not have ZTE use the same backdoor on other models. 

Cataloging and limiting suid applications should be a standard unix hardening step. The simplest way in my opinion to find suid binaries is to use this find command:

find / -x -type f -perm +u=s

Files with the suid bit set will run as the user owning the file, not as the user executing the file. This is typically used to allow normal users to execute particular administrative tasks. So verify if you need or don't need to execute a particular binary as normal user before removing the suid bit.

Update: The file has also been found on the ZTE Skate.

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Johannes B. Ullrich, Ph.D.
SANS Technology Institute
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