IT IS easy to imagine Vladimir Putin gloating amid the revelations that Russia’s foreign intelligence service penetrated multiple U.S. agencies and many private companies in what some are calling the most successful hack of U.S. targets in history. Moscow’s cyberspies have once again demonstrated an extraordinary capacity to exploit the vulnerabilities of an open society wedded to the Internet, just as they did during the 2016 presidential election.

Yet Mr. Putin has some reason for chagrin, as well: It turns out that his regime has its own weaknesses in this high-tech era. That has been made clear by the complete exposure of the team from the FSB spy agency that carried out the poisoning of opposition leader Alexei Navalny with a class of banned nerve agents — a sting that culminated on Monday with the stunning revelation that Mr. Navalny had phoned one of the agents and duped him into providing details of the operation.

Mr. Navalny, who for years has been Mr. Putin’s most determined and effective opponent, nearly died Aug. 20 after he fell ill on a flight. Laboratories in three Western countries and the Organization for the Prohibition of Chemical Weapons subsequently confirmed that he had been attacked with Novichok, a nerve agent developed by the Soviet Union. Mr. Navalny was saved when his plane made an emergency landing and paramedics waiting on the tarmac quickly treated him; he was later evacuated to Germany, where he has remained since.

The episode might have remained murky — Mr. Putin’s government, of course, denied responsibility — if not for an investigation launched by a multinational group of news organizations, led by the Bellingcat website. Taking advantage of Russia’s black market in data — a symptom of the country’s pervasive corruption — investigators were able to purchase phone records and travel manifests that, in turn, allowed them to identify the members of the FSB team, along with their movements. “I know who wanted to kill me,” Mr. Navalny said in a video released with the journalists’ report last week. “I know where they live. I know where they work. I know their real names. I know their fake names. I have photographs of them.”

Not until Monday did Bellingcat drop the most astonishing piece of evidence: a 49-minute recorded phone call between Mr. Navalny and Konstantin Kudryavtsev, a member of the FSB team sent to the city of Omsk to clean up the evidence of the poisoning. The dissident managed to convince the spy that he was a supervisor conducting an after-action investigation, and induced him to describe the action in detail. Among other things, Mr. Kudryavtsev made clear that the FSB intended to kill Mr. Navalny and blamed its failure on the quick work of the plane pilot and paramedics; he also revealed that the Novichok agent had been smeared on Mr. Navalny’s underpants.

The revelations are an acute embarrassment for Mr. Putin, himself a former spy: One of the FSB’s most sensitive units, involved in staging attacks with weapons banned by an international treaty, has now been thoroughly revealed. The information gathered by the investigation — including Mr. Kudryavtsev’s unwitting confession — provides a road map for the United States and other governments to sanction those involved in the attempted murder and in Russia’s illegal use of chemical weapons. It’s not yet known whether the hacking of U.S. agencies was an intelligence operation or an offensive attack meant to damage or disrupt U.S. government operations. But we know exactly what the assault of Mr. Navalny was and who carried it out. There must be consequences.

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