Microsoft on Friday revealed that the Kremlin-backed threat actor known as Midnight Blizzard (aka APT29 or Cozy Bear) managed to gain access to some of its source code repositories and internal systems following a hack that came to light in January 2024.
“In recent weeks, we have seen evidence that Midnight Blizzard is using information initially exfiltrated from our corporate email systems to gain, or attempt to gain, unauthorized access,” the tech giant said.
“This has included access to some of the company’s source code repositories and internal systems. To date we have found no evidence that Microsoft-hosted customer-facing systems have been compromised.”
Redmond, which is continuing to investigate the extent of the breach, said the Russian state-sponsored threat actor is attempting to leverage the different types of secrets it found, including those that were shared between customers and Microsoft in email.
It, however, did not disclose what these secrets were or the scale of the compromise, although it said it has directly reached out to impacted customers. It’s not clear what source code was accessed.
Stating that it has increased in its security investments, Microsoft further noted that the adversary ramped up its password spray attacks by as much as 10-fold in February, compared to the “already large volume” observed in January.
“Midnight Blizzard’s ongoing attack is characterized by a sustained, significant commitment of the threat actor’s resources, coordination, and focus,” it said.
“It may be using the information it has obtained to accumulate a picture of areas to attack and enhance its ability to do so. This reflects what has become more broadly an unprecedented global threat landscape, especially in terms of sophisticated nation-state attacks.”
The Microsoft breach is said to have taken place in November 2023, with Midnight Blizzard employing a password spray attack to successfully infiltrate a legacy, non-production test tenant account that did not have multi-factor authentication (MFA) enabled.
The tech giant, in late January, revealed that APT29 had targeted other organizations by taking advantage of a diverse set of initial access methods ranging from stolen credentials to supply chain attacks.
Midnight Blizzard is considered part of Russia’s Foreign Intelligence Service (SVR). Active since at least 2008, the threat actor is one of the most prolific and sophisticated hacking groups, compromising high-profile targets such as SolarWinds.