Light leak from sun, in Cycles

Subdivision treats the syptoms, not the cause. The source of the problem is the terminator artifact ray biasing, which can be adjusted or even turned off:

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The geometry offset defaults to .1, turn it to zero to negate this artifact.

If you start running into shadow terminator artifacts, then you will need to find a happy medium, but I generally find that I rarely ran into issues with those artifacts. I generally avoid high contrast small light sources and low poly smooth shaded models, but, as always, YMMV.

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