I’ve noticed this in a couple different projects, but it looks like the combination of bloom + HDR in Unity 5 has a tendency to just totally go nuts:
No HDR:
HDR:
It looks like that one little specular pixel is just getting blown way the hell out of proportion in the post-processing shaders. Is there any solution/workaround for this? I love my bloom and HDR. 
Oh, it may be worth noting that I’ve only ever seen this graphical artifact when using Substance materials.
And now that I’m not as dumb, these screens will actually show up.
Yeah, it looks like you’re correct. Actually, what it looks like is that you have a basically mirror smooth surface, and of course in PBR the smoother your surface the smaller and more intense the specular highlight - so with a perfect mirror finish, you get an incredibly small and incredibly intense highlight which gets picked up by the bloom.
You can try making your surface more rough, to make the highlight larger and less intense.
That doesn’t seem to do the trick.
I encountered this problem a couple of times. In most cases the specular map is missing its alpha channel. The alpha channel stores the roughness value but if it is not there unity defaults to full white (which is broken).
If the alpha channel is there you might want to make sure you dont have any pixel with a calue of 255 (white). If it dosnt help you have a different problem than I am used to 
Is this applicable even when using the standard (metal/roughness) shader?
For metalness, isn’t the roughness still stored in alpha?
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Indeed it is. Clamping that to [0,1] solved the problem.
And it has been replaced by this lovely thing (spec from the RTP terrain shaders, I’m guessing):
You mean this isn’t what you were going for?
On a serious note, from what little I can see it looks like your terrain is indeed very shiny. I don’t know much about the RTP pack however.
I believe roughness/smoothness is stored in alpha in both the standard shaders
Hey now… in the future we have brighter light bulbs
And more powerful energy sources.
And camera lenss that enhance light on otherwise unreflective surfaces.
no…not camera lenses, it’s enhanced eyes. And the lens flare can be toggled…