It may be possible to reverse the genophage by extracting an immunity from the galactic data of a cured krogan female. A salarian geneticist named Maelon, a former student of Dr. Mordin Solus, discovered the cure through unethical experimentation on live subjects.
The complexity and durability of the genophage derives from biochemical countermeasures that the salarians wove into the plague in an attempt to make the sterilization incurable. No one is certain of how Maelon circumvented the countermeasures, but his work was complete enough to allow replication of his results.
In its original form, the cure restored fertility but severely compromised the immune system. This resulted in slow, painful death for all but one of Maelon's test subjects. If the beneficial aspects of the cure can be isolated, a specifically tailored virus could repair the affected genes in other krogan.