Ruling on Anat Kamm's appeal against the length of her sentence, the court said it was disproportionate to the penalty of four months of community service imposed on Uri Blau, a reporter for Haaretz, an Israeli left-wing daily.
Some of the 700 classified documents copied by Kamm, a clerk in a general's headquarters during her 2005-2007 army service, were the basis for reports by Blau that some assassinations of Palestinian militants authorized by senior officers may have violated Israeli law.
In 2006, the Supreme Court ruled the military had the right to assassinate members of Palestinian groups that Israel classifies as terrorist organizations. But the court said planners must have "strong and convincing" information that a killing is necessary and always try to avoid harming bystanders.
Although Blau's reports were submitted to the military censor, who approved their publication, he was accused of illegally possessing classified documents and agreed to a plea bargain in July.
Kamm, who cited ideological motives for her actions, admitted in a plea bargain to charges of espionage, collection and possession of secret information and passing it onwards. She began serving her sentence in November 2011.
(Writing by Jeffrey Heller; Editing by Mark Heinrich)