CVE-2024-55591
CVE-2024-55591 is a security flaw in Fortinet FortiOS and FortiProxy, the operating system on Fortinet’s FortiGate firewalls. Attackers can get into Fortinet FortiOS and FortiProxy without a valid password. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 14 Jan 2025, and says ransomware gangs have used it.[1]
Fortinet FortiOS and FortiProxy 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. Fortinet has published a fix or advice.
Description
CISA calls it an authentication bypass in Fortinet FortiOS and FortiProxy. In its words: “Fortinet FortiOS and FortiProxy contain an authentication bypass vulnerability that may allow an unauthenticated, remote attacker to gain super-admin privileges via crafted requests to Node.js websocket module.”[1]
The CVE record adds: “An Authentication Bypass Using an Alternate Path or Channel vulnerability [CWE-288] affecting FortiOS version 7.0.0 through 7.0.16 and FortiProxy version 7.0.0 through 7.0.19 and 7.2.0 through 7.2.12 allows a remote attacker to gain super-admin privileges via crafted requests to Node.js websocket module.”[2]
The underlying weakness is authentication bypass (CWE-288), in MITRE’s list of common software weaknesses.
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; Fortinet’s advisory has them[3]. CISA names the product as Fortinet FortiOS and FortiProxy.
Most families won’t have Fortinet FortiOS and FortiProxy; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 14 Jan 2025, within a day of it being made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 21 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 automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Fortinet 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.Fortinet FortiOS and FortiProxy 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 21 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 Fortinet FortiOS and FortiProxy flaws
- CVE-2025-24472: authentication bypass ·
- CVE-2018-13383: out-of-bounds write ·
- CVE-2018-13382: improper authorization ·
Other Fortinet flaws
- CVE-2025-61624, Fortinet products: path traversal ·
- CVE-2026-104286, Fortinet FortiMail: path traversal ·
- CVE-2025-25249, Fortinet products: heap-based buffer overflow ·
- CVE-2025-68686, Fortinet FortiOS: exposure of sensitive information to an unauthorized actor ·
- CVE-2026-39808, Fortinet FortiSandbox: OS command injection ·
Other authentication bypass flaws
- CVE-2026-20079, Cisco Secure Firewall Management Center (FMC) and Security Cloud Control (SCC) Firewall Management: firewall management center authentication bypass using an alternate path or channel ·
- CVE-2026-19490, Citrix NetScaler: authentication bypass using an alternate path or channel ·
- CVE-2026-18556, N-able N-central: authentication bypass using an alternate path or channel ·
- CVE-2026-18577, N-able N-central: authentication bypass using an alternate path or channel ·
- CVE-2026-1603, Ivanti Endpoint Manager (EPM): authentication bypass ·
Added the same day
- CVE-2025-21335, Microsoft Windows: hyper-V NT kernel integration VSP use-after-free ·
- CVE-2025-21334, Microsoft Windows: hyper-V NT kernel integration VSP use-after-free ·
- CVE-2025-21333, Microsoft Windows: hyper-V NT kernel integration VSP heap-based buffer overflow ·
Every Fortinet flaw on CISA’s list · Everything added in January 2025
References
- ^ Cybersecurity and Infrastructure Security Agency. “Fortinet FortiOS and FortiProxy Authentication Bypass Vulnerability”. Known Exploited Vulnerabilities Catalog, added 14 Jan 2025.
- ^ National Institute of Standards and Technology. “CVE-2024-55591 Detail”. National Vulnerability Database, published 14 Jan 2025.
- ^ Fortinet. Advisories and fixes: fortiguard.fortinet.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.944, percentile 99.9, 31 Oct 2026.
- CVE Program. “CVE-2024-55591”. 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.