They aren’t, but there isn’t as much radiation where the ISS is as there was on the Moon.

The Apollo astronauts were in significant danger from solar storms. There actually was a solar storm during the Apollo missions, in August 1972, but luckily there were no astronauts on the Moon at the time. It was after the Apollo 16 mission ended in April and before Apollo 17, the last mission to the Moon in December. See Sickening Solar Flares

If it had happened during an EVA of the Apollo astronauts they would have been exposed to an estimated 400 REM. There 300 REM is the dose where many of those exposed die. So they were at serious risk there. Though, they would have been rushed straight into radiation treatment when they got back to Earth and maybe they could have survived.

But if they had been on the Moon with such a giant sun spot even without knowing if it would send a solar storm to Earth, maybe they would have just cancelled the EVA and stayed in or close to the lunar module. In that case they could have used it as a storm shelter which would have reduced their exposure to a very survivable. 35 rem

These are things that we will have to take account of if we send astronauts back to the Moon. It’s the same on or in orbit around Mars also, unless you are in a cave of course. And in Mars orbit well Phobos’s crater Stickney gives a fair bit of protection from solar storms, mainly because a base there has the sun either hidden behind Mars or below the crater rim for all except a few hours of each Deimos orbit - it is tidally locked with Stickney facing towards Mars..

The Venus upper atmosphere is even safer, protected by the equivalent of the Earth’s atmosphere, or 10 meters thickness of water equivalent above the astronauts.

So the safest places in the solar system for EVAs for solar storms are:

In low Earth orbit, you get a fair bit of protection from the Earth’s magnetic field, especially for the deadly solar storms. Though you’d schedule your EVA to minimize your exposure to radiation of course :).

Inside caves like this one on Marius hills on the Moon:

In Stickney crater on Mars’ innermost moon Phbos, in the regions most sheltered from the sun.

Faces Mars permanently and protected from much of the effects ofsolar storms and cosmic radiation. See To Explore Mars With Likes Of Occulus Rift & Virtuix Omni - From Mars Capture Orbit, Phobos Or Deimos

Venus clouds, almost complete protection from solar storms because of the atmosphere above you, as on Earth, equivalent to ten meters thickness of water in mass.

Will We Build Colonies That Float Over Venus Like Buckminster Fuller's "Cloud Nine"?

There isn’t any practical way to shield spacesuits from solar storms.

You can shield rovers though to some extent and provide storm shelters inside for astronauts to retreat to. And can shield habitats much more thoroughly.

And just not do EVAs when there seems likely to be an increased risk of solar storms. But another possible future solution is that the astronauts may spend much of their time indoors controlling robotic avatars on the surface via telepresence. It’s surely the safest way to explore, especially if we need to spend years on end doing EVAs,which you never know, we might in the future. And as our telerobots get more capable I think we will get a lot more of that. It might reach the point where EVAs are mostly recreational.