CVE-2024-55956
CVE-2024-55956 is a security flaw in Cleo products, software companies use to send and receive files. Attackers can upload a file to Cleo products from anywhere, without logging in and make it run. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 17 Dec 2024, and says ransomware gangs have used it.[1]
Cleo products is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Cleo has published a fix or advice.
Description
CISA calls it an unauthenticated file upload in Cleo Multiple Products. In its words: “Cleo Harmony, VLTrader, and LexiCom, which are managed file transfer products, contain an unrestricted file upload vulnerability that could allow an unauthenticated user to import and execute arbitrary bash or PowerShell commands on the host system by leveraging the default settings of the Autorun directory.”[1]
The underlying weakness is CWE-276, in MITRE’s list of common software weaknesses.[2]
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Cleo’s advisory has them[3]. CISA names the product as Cleo Multiple Products.
Most families won’t have Cleo products; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 17 Dec 2024, 4 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 7 Jan 2025 to fix it.[1] CISA says ransomware gangs have used it.
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 94%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Cleo has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.Cleo products is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 7 Jan 2025 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 94%.[4] |
See also
Other Cleo products flaws
- CVE-2024-50623: unrestricted file upload ·
Similar flaws
- CVE-2026-87886, Acronis Backup: incorrect default permissions ·
- CVE-2024-51378, CyberPersons CyberPanel: incorrect default permissions ·
- CVE-2024-51567, CyberPersons CyberPanel: incorrect default permissions ·
- CVE-2022-22948, VMware vCenter Server: incorrect default file permissions ·
References
- ^ Cybersecurity and Infrastructure Security Agency. “Cleo Multiple Products Unauthenticated File Upload Vulnerability”. Known Exploited Vulnerabilities Catalog, added 17 Dec 2024.
- ^ National Institute of Standards and Technology. “CVE-2024-55956 Detail”. National Vulnerability Database, published 13 Dec 2024.
- ^ Cleo. Advisories and fixes: support.cleo.com, support.cleo.com, support.cleo.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.940, percentile 99.8, 31 Oct 2026.
- CVE Program. “CVE-2024-55956”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.