mold behind drywall near plumbing 52

https://acornmetric.com/s/whwV9RK8k32JKjoybfD92

There's a musty smell in the bathroom that got worse after a leak, and when I peeled back a corner of the drywall near the plumbing, I found black mold creeping along the paper surface. It seems the moisture from a slow pipe drip has been feeding it, and now the wall feels soft in spots. I'm worried about what's behind the rest of it.