CriticalCVE-2024-50623

    Cleo Multiple Products Unrestricted File Upload Vulnerability (CVE-2024-50623)

    Published Last modified In CISA KEV since Sources: CVE.org, pwn.watch

    What is affected, what to do

    In Cleo Harmony before 5.8.0.21, VLTrader before 5.8.0.21, and LexiCom before 5.8.0.21, there is an unrestricted file upload and download that could lead to remote code execution.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Cleo Harmony to version 5.8.0.21, Cleo Lexicom to version 5.8.0.21, Cleo Vltrader to version 5.8.0.21. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Cleo Harmony lt *..5.8.0.21
    • Cleo Lexicom lt *..5.8.0.21
    • Cleo Vltrader lt *..5.8.0.21
    Fixed in
    • Cleo Harmony 5.8.0.21
    • Cleo Lexicom 5.8.0.21
    • Cleo Vltrader 5.8.0.21

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    9.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org, pwn.watch

    98.6 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.92

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    260.59 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploitedSource: VulnCheck KEV (opens in a new tab) How we classify
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    9.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    9.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    98.6 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.92
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-434

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication and yields full code execution on systems that handle sensitive business data exchanged with trading partners. MFT platforms are a favoured target for mass exploitation followed by data-theft extortion, and CISA flags known use in ransomware campaigns. Exploitation likelihood ranks among the very highest of all scored CVEs. Treat any internet-facing Cleo instance as a top-priority emergency and assume it may already be compromised. Internal-only instances remain critical, but they can be patched second once perimeter exposure is closed.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Establish exposure now: Inventory every Cleo Harmony, VLTrader and LexiCom instance (including DMZ, test and partner gateways) and check whether the web UI or HTTP(S) listeners are reachable from the internet. Default ports are commonly 5080/5443; verify against the local configuration.
      • Cut internet access: Until hardened, restrict inbound access at the perimeter firewall to known trading-partner IPs (allowlist) or take the service offline temporarily. Limit outbound internet traffic from Cleo hosts to what the business strictly requires.
      • Patch: Upgrade to at least 5.8.0.21. Note that this release was later found to be insufficient on its own (follow-up CVE-2024-55956, also on KEV). Look up the currently recommended build in the Cleo vendor advisory and install that directly.
      • Disable Autorun: In the Cleo configuration under Options → Other, clear the "Autorun Directory" field. The observed exploitation chain drops files into the autorun directory, which then execute automatically.
      • Hunt before you patch: Inspect the install directory and the autorun\ and hosts\ subfolders for unexpected .xml, .txt and .jar files. Preserve evidence (disk image, logs) before removing anything. Isolate suspicious hosts rather than just cleaning them.
      • Rotate secrets: If compromise is suspected, rotate all partner credentials, AS2/SFTP keys, certificates and service accounts stored on the host. Notify trading partners of possible data exposure and assess your NIS2 early-warning obligation (24 h).

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place MFT servers in a dedicated DMZ zone. Allow connections from that zone into the internal network only to defined backend systems and ports. Block SMB, RDP and WinRM lateral movement originating from the MFT zone.
      • WAF/IPS: Block or alert on requests to /Synchronization carrying a VLSync header from non-approved sources. Enable the vendor or community signatures for this CVE in your ruleset (ET Open/Pro, vendor IPS).
      • Egress filtering: Restrict outbound traffic from Cleo hosts to partner endpoints only. Deny direct connections to arbitrary internet IPs on high ports to break backdoor callback channels.
      • Endpoint hardening: Use an EDR rule or AppLocker/WDAC to prevent the Cleo Java process from spawning cmd.exe, powershell.exe or rundll32.exe. Enable PowerShell Constrained Language Mode and Script Block Logging.
      • Least privilege: Run the Cleo service under a dedicated, minimally privileged service account rather than LocalSystem or root. Restrict write permissions on the program and autorun directories.

    3. Runbook step 3

      Detection rules

      • EDR/Sysmon EID 1 or Windows Event 4688: A parent process of java.exe/javaw.exe or Harmony.exe/VLTrader.exe/LexiCom.exe spawns cmd.exe or powershell.exe, often with -enc or DownloadString. KQL: DeviceProcessEvents | where InitiatingProcessFolderPath has_any ("Harmony","VLTrader","LexiCom") and FileName in~ ("cmd.exe","powershell.exe")
      • Sysmon EID 11 (FileCreate): New files in ...\autorun\ or new .jar files in the Cleo root directory, especially names like healthcheck*.txt or GUID-style .jar names. Sigma shape: TargetFilename|contains: '\autorun\' combined with an Image under a Cleo path.
      • Web/Cleo access logs: Bursts of requests to /Synchronization with a VLSync header from unfamiliar source IPs, particularly with path-traversal sequences (..\ or ../) in parameters. SPL: index=proxy uri_path="/Synchronization" | stats count by src_ip
      • Network telemetry (Zeek/Suricata): New outbound connections from the MFT host to non-partner IPs, unusually large outbound data volumes (exfiltration), and beaconing patterns in conn.log.
      • Linux (auditd): execve events whose ppid is the Cleo Java process, launching /bin/sh, bash, curl or wget. Rule: -a always,exit -F arch=b64 -S execve -F uid=<cleo-user> -k cleo_exec

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    In Cleo Harmony before 5.8.0.21, VLTrader before 5.8.0.21, and LexiCom before 5.8.0.21, there is an unrestricted file upload and download that could lead to remote code execution.

    Source: cvelistv5, pwn.watch, NVD (NIST), CISA KEV Catalog, CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    cleoharmony
    • < 5.8.0.21
    • 5.8.0.21
    cleolexicom
    • < 5.8.0.21
    • 5.8.0.21
    cleovltrader
    • < 5.8.0.21
    • 5.8.0.21

    Vendors and products

    Weakness classes (CWE)

    • CWE-434Unrestricted Upload of File with Dangerous Type

      Base

      The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.

      Entry at MITRE CWE-434

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • support.cleo.comhc/en-us/articles/27140294267799-Cleo-Product-Security-Advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2024-50623government-resource
    • pwn.watchpwn.watch: Cleo file transfer zero-days exploited by Clop for data theftpwn-watch
    • huntress.comCleo software actively being exploited in the wildpwn-watch
    • support.cleo.comCleo Product Security Update: CVE-2024-55956pwn-watch
    • bleepingcomputer.comClop ransomware claims responsibility for Cleo data theft attackspwn-watch
    • support.cleo.comCleo advisory: CVE-2024-50623pwn-watch
    • NVD (NIST)NVD: CVE-2024-50623pwn-watch
    • NVD (NIST)NVD: CVE-2024-55956pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. Modified Analysisnvd@nist.gov

    2. CVE Modifiedcve@mitre.org

      • Reference: after https://support.cleo.com/hc/en-us/articles/27140294267799-Cleo-Product-Security-Advisory
      • Reference: before https://support.cleo.com/hc/en-us/articles/27140294267799-Cleo-Product-Security-Advisory
      • Reference Type: before https://support.cleo.com/hc/en-us/articles/27140294267799-Cleo-Product-Security-Advisory Types: Vendor Advisory

    3. CVE Modified134c704f-9b21-4f2e-91b3-4a467353bcc0

      • CWE: before CWE-434
      • Affected: after Affected value removed. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2024/50xxx/CVE-2024-50623.json">CVE-2024-50623</a>
      • Reference: after https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-50623
      • Reference: before https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2024-50623
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