White Mortar-like material oozing out of Chimney's brickwork (pictured)
It is efflorescence. Water picks up minerals in the mortar and transports them until the water evaporates, leaving the minerals behind. Other than cosmetic issues, this is normally harmless, though if the process continues for a long period, enough minerals can be removed that the mortar sort of rots.

Only close inspection will indicate if the mortar is compromised. If it is, it's likely superficial and can be corrected by repointing. The deposits can be removed with muriatic acid. The mortar can be protected from more water incursion by applying any of various sealing products available.