Unfortunately, The Tech Report writes Android devices are still at risk because the patch for the Stagefright security bugs did not fully protect devices. It appears it's still possible to create a buffer overflow and execute code via a malformed MP4 file:
The Exodus blog post walks through the vulnerability. A function in libStagefright reads two values from an MP4 file's header, chunk_size and chunk_type, as 32-bit integers. If the header returns a value of 0x01 for chunk_size, then a 64-bit value is read from the MP4 instead. According to the researchers, if an MP4 is crafted with a chunk size of 0x1fffffff (or any other value outside the bounds of a 32-bit integer), a flaw in the Stagefright patch's boundary-checking code means it's still possible to cause a buffer overflow.