CISA issues warning over Medusa ransomware after 300 victims from critical sectors impacted

CISA has issued an alert over ongoing activity linked to the Medusa ransomware as a service (RaaS) group, warning it has impacted hundreds of critical organizations.

The agency issued a joint advisory alongside the FBI and the Multi-State Information Sharing and Analysis Center (MS-ISAC), stating that as of February 2025 Medusa developers and affiliates had hit over 300 victims in the US spanning a “variety of critical infrastructure sectors”.

It said the affected organizations came from a wide range of critical industries such as the education, medical, legal, insurance, technology, and manufacturing sectors.

According to CISA, the Medusa ransomware variant has been in use from 2021, originally operating as a closed ransomware variant but has since transitioned to using an affiliate model.

Yet despite its adoption of a more distributed operating structure, the advisory noted that “important operations such as ransom negotiation are still centrally controlled by the developers.”

The group rose to prominence in 2023 after a string of high profile attacks including one on car manufacturer Toyota and the Minneapolis Public Schools board.

According to new research by Symantec, Medusa ransomware attacks increased by 42% between 2023 and 2024, and warned its activity escalated in recent months.

For example, Symantec found there were nearly twice as many attacks linked to the Medusa RaaS operation in January and February 2025 compared to the first two months of 2024.

How the Medusa ransomware group targets victims

The group is known to traditionally gain access to victim networks by exploiting unpatched vulnerabilities in internet-facing applications, particularly Microsoft Exchange Servers, Symantec warned.

Symantec highlighted another popular tactic frequently employed by the group: the bring your own vulnerable driver (BOYVD) technique.

“[A]ttackers will deploy a signed vulnerable driver to the network, which they then exploit to disable security software and evade detection,” the report explained.

“BYOVD is a technique that has been increasingly used in ransomware attack chains over the last two years. In almost all Medusa attacks, KillAV and associated vulnerable drivers are used in this part of the attack chain to download drivers and disable security software.”

The joint advisory from CISA, the FBI, and MS-ISAC provided a series of mitigations businesses can implement to improve their cybersecurity posture.

This includes keeping all operating systems, software, and firmware up to date and prioritizing patching known exploited vulnerabilities in internet--facing systems.

Other important defensive precautions include network segmentation to prevent lateral movement, requiring multi factor authentication on as many services as possible, and filtering network traffic to prevent unknown actors access remote services or internal systems.

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