Cleo MFT Zero-Day Exploits Are About Escalate, Analysts Warn

An active ransomware campaign against the Cleo managed file transfer tool is about to ramp up now that a proof-of-concept exploit for a zero-day flaw in the software has become publicly available. Defenders should brace for widespread deployment of the Cleopatra backdoor and other steps in the attack chain.

The flaw, which is the result of an insufficient patch for an arbitrary file write tracked as CVE-2024-50623, is being used for remote code execution (RCE) and impacts Cleo Harmony, Cleo VLTrader, and Cleo LexiCon products, according to the company's security advisory. The new issue does not yet have a CVE or CVSS severity score as of the time of this writing.

Active attacks against the zero-day appear to have begun on Dec. 3, and just days later cyberattackers had breached at least 10 Cleo clients, including those in the trucking, shipping, and food industries. Cleo currently has more than 4,000 customers, mostly mid-sized organizations.

The current ransomware campaign has been attributed to a group called "Termite," which is also believed to be connected to similar cyberattacks against Blue Yonder that ultimately impacted household brand names like Starbucks.

But that's just a taste of what's to come, according to Artic Wolf analysts, who predict that ransomware cyberattacks against vulnerable Cleo systems are about to escalate.

Is a MOVEit-Style Deluge of Cyberattacks Imminent?

Since 2023's ransomware success against MOVEit, a similar file transfer service, threat actors have become keenly aware of the broad access to sensitive enterprise data and systems these MFT solutions provide, researchers at Artic Wolf noted.

That's especially true in light of a public proof of exploit of the Cleo zero-day published on Dec. 11 by Watchtowr Labs, the researchers predicted. Like MOVEit, Cleo has the potential to offer attackers a mass-attack avenue.

And unfortunately for those impacted, patching this zero-day has been a bit confusing for Cleo customers, widening the door for attackers to pounce.

The original bug, CVE-2024-50623, was first "fixed" in the Oct. 30 release of an updated Cleo version, 5.8.0.21. However, customers continued to report compromises, "suggesting the existence of a separate means of compromise," a new backgrounder from Rapid7 on the Cleo zero-day explained.

Researchers at Huntress first reported on continued widespread active exploits of the supposedly patched vulnerability on Dec. 9. Cleo responded with a new version containing a new security patch (version 5.8.0.24). However, the new exploitable issue has not yet received a new CVE designation, raising questions from industry watchers like Rapid7.

"Cleo issued a new advisory as of December 10 that previously said versions up to 5.8.0.21 were vulnerable to an as-yet-unassigned CVE," a Rapid7 blog post noted. "That advisory was updated to indicate a patch is now available for all affected products — it's unclear exactly when the update occurred. There is still no CVE for the new issue."

Cleo has since added a note to its advisory page on the insufficient patching issue that a "CVE is pending."

Cleopatra Backdoor: How to Tell if Cleo Has Been Compromised

With the added patching confusion, it's up to cyber defense teams to understand what a Cleo compromise looks like and stop it before it takes hold.

The Artic Wolf team tracked the attack chain down to a malicious PowerShell stager that ultimately executes a new Java-based backdoor that their team appropriately called "Cleopatra."

"The Cleopatra backdoor supports in-memory file storage, and is designed for cross-platform support across Windows and Linux. It implements functionality designed to access data stored within Cleo MFT software specifically," the Artic Wolf report explained. "Although many IP addresses were used as C2 destinations, vulnerability scanning originated from only two IP addresses."

The Arctic Wolf researchers urge defenders to focus in on monitoring server assets for unusual activity, like PowerShell, in order to respond early in the attack chain.

"Additionally, devices should be continuously audited for potential weaknesses in internet-accessible services, and vulnerable services should be kept off the public Internet where possible to minimize the potential exposure in mass exploitation campaigns such as this one," the report added. "This can be accomplished by IP access control lists, or by keeping applications behind a VPN to reduce the potential attack surface."