According to a blog post from TrustedSec, an information security consultancy in Ohio, the breach at Community Health Systems (CHS) is the result of attackers targeting a flaw OpenSSL, CVE-2014-0160, better known as Heartbleed.
The incident marks the first case Heartbleed has been linked to an attack of this size and type.
On Monday, CHS disclosed a data breach in an 8-K filing with the U.S. Securities and Exchange Commission. The filing itself was brief, offering few details on the actual attack and its root cause.
The regulatory notice stated that CHS believes the network compromise itself happened in April and June of 2014. Once discovered, they hired Mandiant to perform an investigation, which speculated that the attacker was part of a group in China.
"The attacker was able to bypass [CHS'] security measures and successfully copy and transfer certain data outside [CHS]," the 8-K explained.
"However, in this instance the data transferred was non-medical patient identification data related to [CHS'] physician practice operations and affected approximately 4.5 million individuals who, in the last five years, were referred for or received services from physicians affiliated with [CHS]."
As mentioned, the 8-K filing itself didn't disclose any of the details behind the attack. However, TrustedSec, has released additional information on the incident, including the root cause, thanks to "a trusted and anonymous source close to the CHS investigation."
"The initial attack vector was through the infamous OpenSSL "heartbleed" vulnerability which led to the compromise of the information," the TrustedSec blog explained.
According to TrustedSec's source, the attackers leveraged Heartbleed and gain user credentials from a Juniper device on the CHS network. From there, the credentials were used to login to the company's VPN.
"From here, the attackers were able to further their access into CHS by working their way through the network until the estimated 4.5 million patient records were obtained from a database," TrustedSec's post added.
Juniper issued updates for their devices 23 days after the issue was publicly revealed. But like other networking vendors, releasing the patches wasn't the final step -- organizations had to apply said patches in order for the issue to even being to be mitigated.
It isn't clear why the CHS device wasn't patched, and the company has made no additional statements.
Unfortunately, CHS may just be the latest, most public victim. Research released on Tuesday by Websense shows an increase in the number of attacks hitting hospitals and medical groups since last October. According to their research, the majority of the attacks are delivered via Heartbleed.