Fair point. Although it's important to note that not any collision attack would work. The collision attack still had to meet certain properties before it coul

Fair point. Although it's important to note that not any collision attack would work. The collision attack still had to meet certain properties before it could be used to successfully attack x509 certificates. So the ability to use this to succesfully attack a git tree from a cryptographic perspective falls somewhere between a collision attack and a pre-image attack. Making the binary blob do something useful also assumes that you know enough about the firmware that you could figure out how to create a valid blob as well as a malicious blob. Very often with these binary blobs the low-level detail of the hardware is not generally available except to the manufacturer --- and if the manufacturer were malicious, they could insert the malware into the official firmware image (or to an update of the official firmware image) in the first place. Finally, the cost estimates in [3] are for a brute force birthday attack, which is definitely not going to be enough for the sort of replacement attack which you are describing. That being said, certainly if we were starting from scratch today, using a newer hash would probably be a good idea. But it's still true that there's a goodly distance from "we can generate a collision" to we can use that to attack a CBA system in real life.