[scatters]

So an attacker able to write to memory would be able to elevate into the ability to... write to memory. That doesn't sound particularly worrisome.

[nocturnial]

In a lot of cases the attacker can only write to a limited range of memory addresses. If that string happens to fall in that range, they can use it to write to other addresses and/or find out where in memory certain things are stored.

So their ability to write to a limited range of addresses can be extended to a larger range.

[a1369209993]

If the attacker can write to string memory, they can overwrite "%s\n\0Hello World" just as easily as "Hello World\n".