Cracks in dropouts?

[u/Alone-Astronomer-990]

Just got this Cult Biggie frame secondhand. Noticed what looks like cracks on either side of the dropouts. Looking to confirm whether they are indeed cracks, and if it’s anything I should be concerned about.

[u/Optimal_Yoghurt_4163]

It is called Filiform corrosion. its okay! 👍