# Cleo file transfer zero-days exploited by Clop for data theft · pwn.watch > Two unauthenticated file-write bugs in Cleo Harmony, VLTrader and LexiCom managed file transfer software (CVE-2024-50623 and CVE-2024-55956) were mass-exploited in December 2024 to plant a Java backdoor and steal data. Huntress saw exploitation from 2024-12-03 against systems already patched to 5.8.0.21; Cleo shipped 5.8.0.24 for the second bug. The Clop ransomware gang claimed the attacks. Added to the CISA KEV catalog on 2024-12-13, 2024-12-17. CISA lists known use in ransomware campaigns. Page: https://pwn.watch/i/cleo-harmony-vltrader-lexicom-zero-days-cve-2024-50623-55956 · generated 2026-10-23T00:16:28.879Z ## Status - Severity: critical · status: closed · patch: patched - Product: Cleo Multiple Products - Started: 2024-12-03 · closed: 2024-12-17 - CVEs: CVE-2024-50623, CVE-2024-55956 - Affected: Cleo Harmony, VLTrader and LexiCom before 5.8.0.24 (Cleo) - Fixed in: 5.8.0.24 (Cleo, for CVE-2024-55956); 5.8.0.21 (Cleo, for CVE-2024-50623) ## Follow this incident - RSS (one item per update): https://pwn.watch/i/cleo-harmony-vltrader-lexicom-zero-days-cve-2024-50623-55956/feed.xml - JSON Feed: https://pwn.watch/i/cleo-harmony-vltrader-lexicom-zero-days-cve-2024-50623-55956/feed.json - Full data (timeline, sources, posts, agentBrief): https://pwn.watch/i/cleo-harmony-vltrader-lexicom-zero-days-cve-2024-50623-55956.json - This file: https://pwn.watch/i/cleo-harmony-vltrader-lexicom-zero-days-cve-2024-50623-55956/llms.txt ## Updates (newest first) - 2024-12-17: CISA added CVE-2024-55956 to the KEV catalog (federal deadline 2025-01-07) (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) - 2024-12-16: Clop claims responsibility for the Cleo data-theft attacks (https://www.bleepingcomputer.com/news/security/clop-ransomware-claims-responsibility-for-cleo-data-theft-attacks/) - 2024-12-14: Cleo advisory: patch 5.8.0.24 for CVE-2024-55956 (https://support.cleo.com/hc/en-us/articles/28408134019735-Cleo-Product-Security-Update-CVE-2024-55956) - 2024-12-13: CVE-2024-55956 published (https://nvd.nist.gov/vuln/detail/CVE-2024-55956) - 2024-12-13: CISA added CVE-2024-50623 to the KEV catalog (federal deadline 2025-01-03) (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) - 2024-12-09: Huntress warns that fully patched 5.8.0.21 systems are still exploitable (https://www.huntress.com/blog/threat-advisory-oh-no-cleo-cleo-software-actively-being-exploited-in-the-wild) - 2024-12-03: Earliest exploitation Huntress observed against Cleo servers (https://www.huntress.com/blog/threat-advisory-oh-no-cleo-cleo-software-actively-being-exploited-in-the-wild) - 2024-10-27: CVE-2024-50623 published (https://nvd.nist.gov/vuln/detail/CVE-2024-50623) ## Fix brief # Security brief: Cleo file transfer zero-days exploited by Clop for data theft Source: https://pwn.watch/i/cleo-harmony-vltrader-lexicom-zero-days-cve-2024-50623-55956 · status: closed (closed Dec 17, 2024) · severity: critical · updated Dec 17, 2024 ## Patch status **PATCHED: fixed releases exist. Upgrade to a fixed version.** ## What it is Two unauthenticated file-write bugs in Cleo Harmony, VLTrader and LexiCom managed file transfer software (CVE-2024-50623 and CVE-2024-55956) were mass-exploited in December 2024 to plant a Java backdoor and steal data. Huntress saw exploitation from 2024-12-03 against systems already patched to 5.8.0.21; Cleo shipped 5.8.0.24 for the second bug. The Clop ransomware gang claimed the attacks. Added to the CISA KEV catalog on 2024-12-13, 2024-12-17. CISA lists known use in ransomware campaigns. Severity detail: CVSS 9.8 (v3.1, CISA-ADP), actively exploited (CISA KEV); known ransomware use - Product: Cleo Multiple Products - CVE / advisory ids: CVE-2024-50623, CVE-2024-55956 ## Affected versions - Cleo Harmony, VLTrader and LexiCom before 5.8.0.24 (Cleo) ## Check whether you're affected No generic command applies (the product is a hosted service, appliance or desktop app). Check the installed version in its admin UI / About screen and compare with the versions above. ## Fix Upgrade to one of these fixed versions (or later on the same branch): - 5.8.0.24 (Cleo, for CVE-2024-55956) - 5.8.0.21 (Cleo, for CVE-2024-50623) After upgrading, re-run the checks above and redeploy/restart the affected services. ## Latest updates - Dec 17, 2024: CISA added CVE-2024-55956 to the KEV catalog (federal deadline 2025-01-07) - Dec 16, 2024: Clop claims responsibility for the Cleo data-theft attacks - Dec 14, 2024: Cleo advisory: patch 5.8.0.24 for CVE-2024-55956 - Dec 13, 2024: CVE-2024-55956 published - Dec 13, 2024: CISA added CVE-2024-50623 to the KEV catalog (federal deadline 2025-01-03) - Dec 9, 2024: Huntress warns that fully patched 5.8.0.21 systems are still exploitable - Dec 3, 2024: Earliest exploitation Huntress observed against Cleo servers - Oct 27, 2024: CVE-2024-50623 published ## Advisories - [Cleo Product Security Update: CVE-2024-55956](https://support.cleo.com/hc/en-us/articles/28408134019735-Cleo-Product-Security-Update-CVE-2024-55956) (Cleo) - [Cleo advisory: CVE-2024-50623](https://support.cleo.com/hc/en-us/articles/28408134019735-Cleo-Product-Security-Update) (Cleo) - [NVD: CVE-2024-50623](https://nvd.nist.gov/vuln/detail/CVE-2024-50623) (NVD) - [NVD: CVE-2024-55956](https://nvd.nist.gov/vuln/detail/CVE-2024-55956) (NVD) - [CISA Known Exploited Vulnerabilities Catalog](https://www.cisa.gov/known-exploited-vulnerabilities-catalog) (CISA) ## Write-ups & news - [Cleo software actively being exploited in the wild](https://www.huntress.com/blog/threat-advisory-oh-no-cleo-cleo-software-actively-being-exploited-in-the-wild) - [Clop ransomware claims responsibility for Cleo data theft attacks](https://www.bleepingcomputer.com/news/security/clop-ransomware-claims-responsibility-for-cleo-data-theft-attacks/) ## Caveats Derived from the CISA KEV JSON feed (catalogVersion 2026.10.21); CVSS from the CVE record (cveawg.mitre.org). startedAt is the CVE publication date when it fell in 2024 before the KEV listing, else the KEV dateAdded; exploitation may have begun earlier. closedAt is the KEV listing date (a fix or mitigation was available then unless noted). --- Machine-readable: https://pwn.watch/i/cleo-harmony-vltrader-lexicom-zero-days-cve-2024-50623-55956.json · all incidents: https://pwn.watch/incidents.json. Verify against the vendor advisory before changing production systems.