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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 3 May 2022. Known ransomware use
FortiosOperating system · Fortinet

CVE-2019-5591

MEDIUM · 6.5 CVSS v3.1 Published 2020-08-14
Fix available
A fix is available. Upgrade to after 6.2.0 or later.
See remediation →
99/100
Remediation priority · Urgent
In the wild Ransomware No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A Default Configuration vulnerability in FortiOS may allow an unauthenticated attacker on the same subnet to intercept sensitive information by impersonating the LDAP server.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

FortiOS contains a default configuration vulnerability where the LDAP server authentication does not properly validate server certificates or uses insecure settings. An unauthenticated attacker on the same subnet can perform a man-in-the-middle attack to impersonate the LDAP server and intercept sensitive authentication credentials.

MitigationChange the default LDAP configuration to enforce LDAPS (LDAP over SSL/TLS) with certificate validation, or implement mutual TLS authentication to prevent LDAP server impersonation.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FortiosOperating system
Affected:<= 6.2.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check FortiOS version
    Run 'get system status' or 'show system version' to retrieve the FortiOS firmware version
    Affected if Version is 6.2.0 or lower (any version up to and including 6.2.0)
  2. Identify configured LDAP servers
    Run 'config user ldap' then 'show' to list all configured LDAP server entries
    Affected if Any LDAP server configuration exists in the FortiOS device
  3. Verify LDAP certificate validation setting
    For each LDAP server entry, run 'get' to display the configuration and check the 'validate-server-certificate' or 'server-validate' parameter
    Affected if The setting is disabled, set to 'disable', or not explicitly configured (using default insecure setting)
  4. Check LDAP transport security mode
    Run 'get' for each LDAP server and check the 'secure' parameter (options: disable, starttls, ssl)
    Affected if The 'secure' parameter is set to 'disable' or is not configured, indicating plain LDAP without TLS/SSL
  5. Confirm LDAP port in use
    Run 'get' for each LDAP server and check the 'port' parameter
    Affected if Port is 389 (plain LDAP) rather than 636 (LDAPS)

A user is affected if their FortiOS version is 6.2.0 or lower AND they have configured LDAP servers with certificate validation disabled or using plain LDAP (port 389) without TLS encryption.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 6.2.0
Interim mitigation

Change the default LDAP configuration to enforce LDAPS (LDAP over SSL/TLS) with certificate validation, or implement mutual TLS authentication to prevent LDAP server impersonation.

Recommended fix Moderate confidence

FortiOS 6.4.0 or later (or FortiOS 6.2.1+ if 6.4.x is not feasible)

  1. Identify the current FortiOS version by running `get system status` or checking the FortiGate GUI dashboard
  2. Backup the current FortiOS configuration using `execute backup config` or via GUI
  3. Download FortiOS 6.4.x or later from Fortinet's support portal (support.fortinet.com)
  4. Upload the firmware image via FortiGate GUI (System > Firmware) or via CLI using `execute firmware upgrade`
  5. Reboot the FortiGate device after firmware installation
  6. Verify the upgrade was successful by running `get system status` and confirm the version is 6.4.0 or higher
  7. Test LDAP authentication functionality to ensure the fix does not impact legitimate operations
Caveat Review FortiOS release notes for 6.4.x for potential configuration or feature changes; some LDAP-related CLI commands may have modified syntax

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Fortios Exploited in the wild — priority engagement
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,570
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2019-5591 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data