Replicant developers found a back-door to be present in "most proprietary Android systems running on the affected Samsung Galaxy devices, including the ones that are shipped with the devices."
The Replicant developers' research finds "Samsung Galaxy devices running proprietary Android versions come with a back-door that provides remote access to the data stored on the device. In particular, the proprietary software that is in charge of handling the communications with the modem, using the Samsung IPC protocol, implements a class of requests known as RFS commands, that allows the modem to perform remote I/O operations on the phone's storage. As the modem is running proprietary software, it is likely that it offers over-the-air remote control, that could then be used to issue the incriminated RFS messages and access the phone's file system."
Among the known affected devices are the Nexus S, Galaxy S, Galaxy S2, Galaxy Note, Galaxy Tab 2, Galaxy S 3, and Galaxy Note 2. The Galaxy S seems to be in the worse shape with the back-doored program running as root.
For those Samsung Galaxy users there is a back-door sample and steps for investigating and analyzing this issue within a Samsung binary blob. In terms of the legitimacy of the backdoor, the developers believe, "the incriminated RFS messages of the Samsung IPC protocol were not found to have any particular legitimacy nor relevant use-case. However, it is possible that these were added for legitimate purposes, without the intent of doing harm by providing a back-door. Nevertheless, the result is the same and it allows the modem to access the phone's storage."
This Galaxy backdoor issue was passed on this morning by Phoronix reader and Twitter follower bashlog. All of the details for the issue are reported on this Replicant Wiki page that now appears to be a few weeks old but hasn't yet generated any widespread attention to the issue.
Those wishing to avoid this potential back-door from being exploited, Replicant OS doesn't contain this Samsung binary blob. The problem for many though is that Replicant's stable release is still Android 4.2 and based upon CyanogenMod 10.1 rather than catching up with upstream Android 4.4. With removing the phone / tablet binary blobs -- including proprietary firmware -- many of these "supported" Replicant devices do not have working 2D/3D acceleration, GPS, NFC, or even camera support in some cases.