No indication of Russia's involvement in JPM hack: Source

JPM hack developments

There is no indication that Vladimir Putin, the Russian government or any foreign nation state was involved in the JPMorgan cyberattack this summer, a source familiar with the incident tells CNBC.

There have been media reports speculating that the Russians may have carried out the attack in retaliation for U.S. sanctions on Russia, but that appears not to be the case, the source said. "Anyone who says this is the Russians, that's ridiculous," the source said. "There's no indication of any foreign nation state. Any reporting on that is not coming from someone who knows what's going on."

The source also provided additional details about what is known about the attack, which has received widespread publicity as an indication of the potential vulnerability of the US financial sector to cyberattacks.

Read More Market ripe for M&A, says JPMorgan exec

Some 13 financial institutions have reported that they saw cyberactivity related to the hack, the source said—but that does not mean data was exfiltrated from their servers. "What that means is someone knocked on the door," the source said. "Whoever it is that was going after JPMorgan was also going after these other financial institutions."

Not among the banks reporting cyberactivity, the source said, was Citibank, despite media accounts to the contrary. "There is no indication that Citi suffered a breach related to the JPMorgan attack," the source said. "Any of that that's out there is just not true."

ETrade, however, did report related cyberactivity, the source said.

The source declined to provide information on what's known about the attackers themselves, or how they got into JPMorgan's systems.

Read More Janus' Gross: The global economy is slowing down

There has been a regular flow of communication back and forth between JPMorgan, the nation's other large financial institutions, and the FBI about what exactly happened in the attack and how the banks can protect themselves. Among the information shared between the banks are the IP addresses of the computers carrying out the attacks, so that other banks can check their logs for hits from the same IP addresses.

On Saturday, however, that process ran into a snafu, when the FBI inadvertently sent an internal investigation update that was not meant for public consumption to a wide range of bank security professionals.

In a follow-up note, the FBI's Cyber Division Section Chief John Riggi wrote, "This draft communication was not intended for dissemination as it contained outdated and inaccurate information and uncorroborated characterizations."

In the same memo, the FBI sought to clarify exactly what it did and did not know about just how sophisticated the attackers of JPMorgan were. "The FBI wanted to confirm for all concerned parties that no attribution or level of expertise regarding the actor has been determined at this time," Riggi wrote.

—Jonathan Dienst and Kayla Tausche contributed to this report.