Exploited vulnerability · CISA KEV

Is CVE-2019-5591 exploited? Yes: in CISA KEV since 3 Nov 2021

Gociux · Fortinet FortiOS · data: CISA KEV, CVE record, FIRST EPSS

Yes. CVE-2019-5591, Fortinet FortiOS Default Configuration Vulnerability, is being exploited in the wild. CISA added it to its Known Exploited Vulnerabilities catalog on 3 Nov 2021, 446 days after it was published. It is known to be used in ransomware campaigns. It affects Fortinet FortiOS, an internet-facing product of the kind attackers use for initial access. If you run it, CISA's required action is: Apply updates per vendor instructions.

What it is

Fortinet FortiOS contains a default configuration vulnerability that may allow an unauthenticated attacker on the same subnet to intercept sensitive information by impersonating the Lightweight Directory Access Protocol (LDAP) server.

What to do

1. Check whether you run it. Look for FortiOS in your asset inventory, including appliances and cloud images. Stack check lists every exploited Fortinet CVE at once.
2. Apply the fix. Apply updates per vendor instructions.
3. If you can't patch today, take the affected service off the internet or restrict who can reach it, and check its logs for signs of compromise since 14 Aug 2020.
4. Get told next time. Email alerts when CISA adds a CVE for Fortinet.

Other exploited CVEs in FortiOS

• CVE-2025-68686: Fortinet FortiOS Exposure of Sensitive Information to an Unauthorized Actor Vulnerability (27 Jul 2026)
• CVE-2019-6693: Fortinet FortiOS Use of Hard-Coded Credentials Vulnerability (25 Jun 2025)
• CVE-2024-21762: Fortinet FortiOS Out-of-Bound Write Vulnerability (9 Feb 2024)
• CVE-2022-41328: Fortinet FortiOS Path Traversal Vulnerability (14 Mar 2023)
• CVE-2022-42475: Fortinet FortiOS Heap-Based Buffer Overflow Vulnerability (13 Dec 2022)
• CVE-2021-44168: Fortinet FortiOS Arbitrary File Download (10 Dec 2021)

References

• nvd.nist.gov/vuln/detail/CVE-2019-5591

Sources: CISA KEV (exploitation, ransomware use, required action, due date), the CVE record (publication date, CVSS, CNA), NVD and FIRST EPSS (live score). More: all KEV additions in November 2021 · Fortinet scorecard · act-now radar.