CriticalCVE-2024-55956

    Cleo Multiple Products Unauthenticated File Upload Vulnerability (CVE-2024-55956)

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

    What is affected, what to do

    In Cleo Harmony before 5.8.0.24, VLTrader before 5.8.0.24, and LexiCom before 5.8.0.24, an unauthenticated user can import and execute arbitrary Bash or PowerShell commands on the host system by leveraging the default settings of the Autorun directory.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Cleo Harmony to version 5.8.0.24, Cleo Lexicom to version 5.8.0.24, Cleo Vltrader to version 5.8.0.24. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Cleo Harmony lt *..5.8.0.24
    • Cleo Lexicom lt *..5.8.0.24
    • Cleo Vltrader lt *..5.8.0.24
    Fixed in
    • Cleo Harmony 5.8.0.24
    • Cleo Lexicom 5.8.0.24
    • Cleo Vltrader 5.8.0.24

    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

    94.0 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.85

    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
    260.96 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
    94.0 %
    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
    99.85
    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

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication or user interaction and yields direct code execution on a system that, by design, handles business data for many partners. CISA flags known ransomware campaign use; MFT platforms are favoured targets for mass exploitation followed by data theft and extortion, with logistics, retail, manufacturing and supply-chain service providers most frequently hit. Exploitation likelihood sits among the very highest of all tracked CVEs. Treat any internet-exposed Cleo instance below 5.8.0.24 as an emergency and as potentially already compromised; internally reachable instances still warrant remediation within days.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Patch now: Upgrade Cleo Harmony, VLTrader and LexiCom to 5.8.0.24 or later. Every build prior to 5.8.0.24 is vulnerable, including earlier 5.8.0.x hotfix releases. Confirm the running version in the admin UI and installation directory after upgrading.
      • Disable Autorun if you cannot patch immediately: In the Cleo configuration (Configure → Options → Other), clear the "Autorun Directory" field and save. Exploitation relies on the default setting of this directory. Restart the service afterwards.
      • Cut exposure: Restrict internet-facing Cleo instances at the perimeter firewall to known trading-partner IPs, or take them offline temporarily. Focus on the HTTP/HTTPS listener ports actually configured (commonly 5080/5443 — verify against your own setup).
      • Compromise assessment before returning to service: Inspect the Autorun directory plus hosts/, temp/ and subfolders of the installation for unknown files (oddly named .txt, .xml or .zip files, unfamiliar .jar files). Preserve evidence (disk image, memory dump) rather than simply deleting artefacts.
      • Rotate credentials: On any suspicion, rotate all partner secrets stored on the host (AS2/SFTP/FTP passwords, private keys, certificates), service accounts and any cached domain credentials. MFT servers concentrate secrets for many counterparties.
      • Check reporting obligations: If data exfiltration is confirmed, prepare the NIS2 early warning (24 h) to your competent authority/CSIRT and, where personal data is involved, the GDPR notification (72 h). Notify affected trading partners.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place Cleo servers in a dedicated DMZ zone. Inbound: partner allowlist on MFT ports only. Outbound: default-deny with explicit partner endpoints. Specifically block arbitrary outbound HTTP(S)/PowerShell traffic, since follow-on stages pull payloads and open reverse connections.
      • WAF/IPS: On a fronting reverse proxy, block uploads to endpoints you do not use and inspect requests to Cleo listeners for path-traversal patterns (../, ..\, URL-encoded variants). Enable vendor IPS signatures for CVE-2024-55956 in blocking mode.
      • Endpoint hardening: Use AppLocker/WDAC or EDR custom rules to prevent the Cleo Java process (javaw.exe/java.exe, or java on Linux) from spawning powershell.exe, cmd.exe, bash or sh. Enforce PowerShell Constrained Language Mode and Script Block Logging.
      • Least privilege: Run the Cleo service under a dedicated non-privileged account (not SYSTEM, not root, never a domain admin). Minimise write access to the installation tree so the service account cannot write into the Autorun directory where operationally feasible.
      • Configuration: Keep Autorun permanently disabled unless strictly required. Turn off unused protocol listeners. Deploy file integrity monitoring (FIM) on the installation and Autorun directories.

    3. Runbook step 3

      Detection rules

      • Process ancestry (Sysmon EID 1 / Windows Event 4688 / EDR): Shell-family children of the Cleo Java process. KQL starter: DeviceProcessEvents | where InitiatingProcessFileName in~ ("javaw.exe","java.exe") and InitiatingProcessFolderPath has_any ("Harmony","VLTrader","LexiCom") and FileName in~ ("powershell.exe","cmd.exe","pwsh.exe"). Escalate encoded PowerShell (-enc, -EncodedCommand) as high severity.
      • File creation in Autorun (Sysmon EID 11 / FIM / auditd): Any new file under ...\autorun\ outside planned maintenance is suspicious. Linux: auditctl -w /<cleo-install>/autorun -p wa -k cleo_autorun. Sigma shape: TargetFilename|contains: '\autorun\' with Image|endswith: '\javaw.exe'.
      • Linux execution (auditd): execve events with exe=/bin/bash or /bin/sh whose parent is java running as the Cleo service account. Also capture curl/wget invoked from that context.
      • Network telemetry (Zeek/Suricata): Outbound connections from the Cleo host to destinations outside the partner allowlist — new destinations, HTTP downloads of .jar/.zip files, and large outbound transfers indicating exfiltration. Zeek conn.log: id.orig_h == <cleo_host> with high orig_bytes to non-partner IPs.
      • Application and access logs: Review Cleo logs and proxy logs for unexpected uploads, requests containing traversal sequences and import activity without a matching partner session. Treat newly created hosts/mailboxes in the Cleo configuration as a persistence indicator.

    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 5.8.0.24, VLTrader before 5.8.0.24, and LexiCom before 5.8.0.24, an unauthenticated user can import and execute arbitrary Bash or PowerShell commands on the host system by leveraging the default settings of the Autorun directory.

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

    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
    • < 5.8.0.24
    • 5.8.0.24
    cleolexicom
    • < 5.8.0.24
    • 5.8.0.24
    cleovltrader
    • < 5.8.0.24
    • 5.8.0.24

    Vendors and products

    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/28408134019735-Cleo-Product-Security-Advisory…
    • support.cleo.comCleo advisory: CVE-2024-50623pwn-watch
    • huntress.comCleo software actively being exploited in the wildpwn-watch
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2024-55956government-resource
    • pwn.watchpwn.watch: Cleo file transfer zero-days exploited by Clop for data theftpwn-watch
    • support.cleo.comCleo Product Security Update: CVE-2024-55956pwn-watch
    • bleepingcomputer.comClop ransomware claims responsibility for Cleo data theft attackspwn-watch
    • NVD (NIST)NVD: CVE-2024-50623pwn-watch
    • NVD (NIST)NVD: CVE-2024-55956pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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