Exploited CVEs / Fortinet / CVE-2019-5591

CVE-2019-5591

Fortinet FortiOS Default Configuration Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted, and the vulnerability is known to be used in ransomware campaigns. Federal agencies were required to remediate by 2022-05-03 (that deadline has passed); treat that date as the outer bound for your own environment. The fix is in the vendor advisory: Fortinet PSIRT Advisories, linked below.

Risk summary

MediumCISA KEVRansomware

6.5

CVSS base

18%

EPSS exploit probability

Medium

Severity

2021-11-03

Added to KEV

2022-05-03 (past due)

CISA due date

Actively exploited Fortinet FortiOS vulnerability, Medium severity, CVSS 6.5. Added to the CISA KEV catalog 2021-11-03.

Senserva AI read on CVE-2019-5591 CISA required action Official fix for CVE-2019-5591 Admin questions

Senserva AI Opinion for CVE-2019-5591

A default configuration weakness in Fortinet FortiOS lets an unauthenticated attacker on the same subnet impersonate the LDAP server and intercept credentials the firewall sends for authentication. State-sponsored actors used it, chained with other FortiOS bugs, to harvest VPN credentials per public advisories. Its Medium Severity rating of CVSS 6.5 understates its role as a credential-theft step in confirmed intrusion campaigns.

Do this: Configure LDAPS with server certificate verification on all FortiGate devices and rotate any directory credentials the firewall uses.

AI-generated from public data, 2026-07-07. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2019-5591

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

I run IT security. Facts for CVE-2019-5591, an actively exploited vulnerability (source: https://senserva.com/cve/CVE-2019-5591.html, data from CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2019-5591: Fortinet FortiOS Default Configuration Vulnerability
- Affected: Fortinet FortiOS
- Severity: Medium, CVSS 6.5; EPSS 30-day exploitation probability 18%
- Added to CISA KEV: 2021-11-03; federal remediation due 2022-05-03
- Ransomware-linked: YES
- CISA required action: Apply updates per vendor instructions.
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) The fastest safe path to remediation. 4) How to check whether my environment is exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Patch immediately

Exploited in the wild and used in ransomware campaigns.

The fix ships from the vendor: Fortinet PSIRT Advisories.

Do this now: Move this ahead of everything else in the queue, then verify the fix actually landed on every exposed device.

Updated August 15, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Full tracking and change history for CVE-2019-5591

Published: 2021-11-03
Last revised: 2021-11-03
Changes tracked: 2

Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.

Senserva Watchevery change we have recorded for this one

What changed, and when

2021-11-03 added to the CISA KEV catalog by CISA
2026-07-17 CVSS 0.0 to 6.5; EPSS first scored at 18.6%
2026-08-11 EPSS 18.6% to 18.4%

Recorded by Senserva on the dates shown, from CISA KEV and FIRST EPSS. This is what moved and when, which neither the vendor advisory nor NVD publishes.

CISA required action

Federal (BOD 22-01) remediation due date: 2022-05-03 (past due).

Apply updates per vendor instructions.

Official fix for CVE-2019-5591

The authoritative fix and affected-version list are published by the vendor. Find the FortiOS advisory on Fortinet PSIRT Advisories.

Fortinet PSIRT Advisories CISA KEV entry

Common questions about CVE-2019-5591

Is CVE-2019-5591 actively exploited?

Yes. CVE-2019-5591 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2021-11-03, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 18%. CISA also reports it is known to be used in ransomware campaigns.

What is the CISA deadline and required action for CVE-2019-5591?

CISA set the federal (BOD 22-01) remediation due date at 2022-05-03, which has passed; treat any unremediated system as overdue. The verbatim required action: Apply updates per vendor instructions.

What fixes CVE-2019-5591?

The authoritative fix is in the vendor advisory: see Fortinet PSIRT Advisories for the patched FortiOS versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.

Can I ask my own AI about CVE-2019-5591?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2019-5591's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed twice a day (5 AM and 3 PM US Central).

Scope and sources

More exploited Fortinet CVEs: CVE-2025-68686 CVE-2026-39808 CVE-2026-25089 CVE-2026-21643 CVE-2026-35616 CVE-2026-24858 CVE-2025-59718 CVE-2025-58034
All Fortinet exploited CVEs on one page: Fortinet vulnerabilities actively exploited.
Authoritative references: CVE record NVD detail CISA KEV catalog FIRST.org EPSS

Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.