When a person or an entity is said to be under attack,it means that they are being targeted by an opponent or enemy, or are facing criticism or challenge. Synonyms for under attack range from phrases like "in the line of fire" or "in the crosshairs" to more direct phrases like "under siege" and "under assault." Other analogous phrases might include "under fire," "under threat," and "under pressure." Depending on the context and the severity of the situation, different synonyms may be more appropriate to use, but all convey the sense of vulnerability and danger that comes with being targeted.