A threat actor is said to have "highly likely" exploited a security flaw in an outdated Atlassian Confluence server to deploy a never-before-seen backdoor against an unnamed organization in the research and technical services sector.

The attack, which transpired over a seven-day-period during the end of May, has been attributed to a threat activity cluster tracked by cybersecurity firm Deepwatch as TAC-040.

"The evidence indicates that the threat actor executed malicious commands with a parent process of tomcat9.exe in Atlassian's Confluence directory," the company said. "After the initial compromise, the threat actor ran various commands to enumerate the local system, network, and Active Directory environment."

The Atlassian vulnerability suspected to have been exploited is CVE-2022-26134, an Object-Graph Navigation Language (OGNL) injection flaw that paves the way for arbitrary code execution on a Confluence Server or Data Center instance.

Following reports of active exploitation in real-world attacks, the issue was addressed by the Australian company on June 4, 2022.

But given the absence of forensic artifacts, Deepwatch theorized the breach could have alternatively entailed the exploitation of the Spring4Shell vulnerability (CVE-2022-22965) to gain initial access to the Confluence web application.

Not much is known about TAC-040 other than the fact that the adversarial collective's goals could be espionage-related, although the possibility that the group could have acted out of financial gain hasn't been ruled out, citing the presence of a loader for an XMRig crypto miner on the system.

While there is no evidence that the miner was executed in this incident, the Monero address owned by the threat actors has netted at least 652 XMR ($106,000) by hijacking the computing resources of other systems to illicitly mine cryptocurrency.

The attack chain is also notable for the deployment of a previously undocumented implant called Ljl Backdoor on the compromised server. Roughly 700MB of archived data is estimated to have been exfiltrated before the server was taken offline by the victim, according to an analysis of the network logs.

The malware, for its part, is a fully-featured trojan virus designed to gather files and user accounts, load arbitrary .NET payloads, and amass system information as well as the victim's geographic location.

"The victim denied the threat actor the ability to laterally move within the environment by taking the server offline, potentially preventing the exfiltration of additional sensitive data and restricting the threat actor(s) ability to conduct further malicious activities."