CVE-2019-5591 — Fortios
MEDIUMCVE-2019-5591 is a medium-severity (CVSS 6.5) Missing Authentication vulnerability in fortinet fortios. It is in CISA's Known Exploited Vulnerabilities catalog (added 2021-11-03) and has been used in ransomware campaigns — treat it as actively exploited and patch now. No vendor fix is recorded yet; mitigation options are listed below.
A Default Configuration vulnerability in FortiOS may allow an unauthenticated attacker on the same subnet to intercept sensitive information by impersonating the LDAP server.
Exploitation Status
Actively exploited in the wild
- Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2021-11-03 — including use in ransomware campaigns. Federal agencies were required to remediate by 2022-05-03.
Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2019-5591.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2019-5591 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 395,249 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.
Description
A Default Configuration vulnerability in FortiOS may allow an unauthenticated attacker on the same subnet to intercept sensitive information by impersonating the LDAP server.
Affected Products
fortiosfortinetResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Vendor / applianceDetect
Inventory every fortinet fortios deployment and check each version against the affected-products list above.
Remediation status
No patch has shipped for CVE-2019-5591 yet — track the fortinet fortios advisory for a fixed release and apply the workarounds below in the meantime.
Mitigate without a patch
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used. Alongside that, restrict the management interface to trusted networks and apply the vendor's recommended configuration mitigations.
How to detect CVE-2019-5591
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id cve-2019-5591 -u https://target- Template
- FortiOS - Insecure LDAP Configuration Detection
- Severity
- medium
- Impact
- Unauthenticated attackers can intercept sensitive information by impersonating LDAP servers within the same subnet.
- Remediation
- Configure LDAP server settings properly and disable default configurations; update to the latest firmware version.
Template by ProjectDiscovery nuclei-templates (ayewo), MIT licensed. View the full template. Scan only systems you are authorised to test.
Frequently Asked Questions
Is CVE-2019-5591 being exploited in your environment?
Detect and block the exploit chain at execution, on systems you cannot patch yet.