CVE-2024-50623

CVE-2024-50623 is an unrestricted file upload and download flaw (CWE-434) in Cleo's managed file transfer products — Harmony, VLTrader, and LexiCom — before version 5.8.0.21. It is reachable over the network with no authentication or user interaction (CVSS 9.8, AV:N/AC:L/PR:N), letting an attacker send crafted requests that upload arbitrary files to the server. The unrestricted upload leads to remote code execution, giving the attacker full control of the host for staging, data theft, or ransomware, while the download capability risks exposure of business files the server moves with trading partners. Any organization running these products is affected, and managed file transfer servers are typically internet-facing and handle sensitive B2B data. Exploitation is confirmed in the wild: CISA added it to the KEV catalog on 2024-12-13 with ransomware use noted, EPSS assigns a 98.6% probability of exploitation within 30 days, and the Clop ransomware gang has claimed dozens of breaches (some disputed), including a confirmed breach at WK Kellogg.

What to do: Upgrade Harmony, VLTrader, and LexiCom to 5.8.0.21 or later per vendor instructions; if upgrading is not possible, apply vendor mitigations or discontinue use of the product, as CISA's KEV entry requires. Prioritize internet-exposed instances, hunt for indicators of compromise (unexpected file writes and execution on the transfer host, new accounts, suspicious outbound connections), and restrict the service to trusted partner networks. Given known ransomware use by Clop, any suspected compromise should trigger checks for lateral movement and staged exfiltration of transferred files.