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FortiwebApplication · Fortinet

CVE-2021-36188

MEDIUM · 6.1 CVSS v3.1 Published 2021-12-08
Fix available
A fix is available. Upgrade to 6.3.16 / 6.4.2 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

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 improper neutralization of input during web page generation ('cross-site scripting') in Fortinet FortiWeb version 6.4.1 and below, 6.3.15 and below allows attacker to execute unauthorized code or commands via crafted GET parameters in requests to login and error handlers

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 · high confidence

FortiWeb versions 6.4.1 and below, 6.3.15 and below contain a stored cross-site scripting (XSS) vulnerability in the login and error handler endpoints. Attackers can inject malicious JavaScript code via crafted GET parameters that are rendered without proper sanitization, allowing execution of unauthorized client-side scripts in the context of authenticated users.

MitigationUpgrade FortiWeb to version 6.4.2 or 6.3.16 or later. As a temporary workaround, implement WAF rules to sanitize or block malicious parameters in login and error handler requests.

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
FortiwebApplication
Affected:>= 6.0.0, <= 6.2.5>= 6.3.0, < 6.3.16>= 6.4.0, < 6.4.2

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
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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 FortiWeb version
    Access the FortiWeb GUI dashboard or use CLI command 'get system status' to retrieve the firmware version
    Affected if version falls within 6.0.0-6.2.5, 6.3.0-6.3.15, or 6.4.0-6.4.1 ranges
  2. Identify exposed login endpoint
    Review web server configuration or firewall rules to determine if the FortiWeb login page (typically /login) is accessible from untrusted networks
    Affected if login endpoint is externally accessible without additional filtering
  3. Identify exposed error handler endpoints
    Check for accessible error handling paths such as /error, /404, or custom error pages served by FortiWeb
    Affected if error handler endpoints are reachable without authentication
  4. Verify WAF XSS protection rules
    In FortiWeb GUI, navigate to Security Profiles > XSS or CLI 'show waf xss' to inspect active XSS filtering configurations
    Affected if no XSS rules exist or rules do not specifically sanitize GET parameters on login/error pages
  5. Test for parameter reflection
    Send a crafted GET request with a test XSS payload (e.g., ?test=<script>alert(1)</script>) to the login or error endpoints and observe if the payload is reflected unescaped in the response
    Affected if payload appears verbatim in the HTTP response without HTML encoding

User is affected if FortiWeb version is 6.4.1 or below, 6.3.15 or below, or 6.2.5 or below AND the login or error handler endpoints are accessible with no XSS sanitization on GET parameters.

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 6.3.16 / 6.4.2 or later
Fixed in 6.3.166.4.2
Interim mitigation

Upgrade FortiWeb to version 6.4.2 or 6.3.16 or later. As a temporary workaround, implement WAF rules to sanitize or block malicious parameters in login and error handler requests.

Recommended fix High confidence

FortiWeb 6.3.16 or 6.4.2 (or later stable releases within the same major version)

  1. 1. Backup the current FortiWeb configuration using the web UI or CLI (execute 'execute backup full-config').
  2. 2. Download the appropriate firmware upgrade from Fortinet Customer Support/FortiGuard for your hardware model.
  3. 3. Upload the new firmware file via FortiWeb web UI (System > Firmware > Upload) or CLI (execute upgrade).
  4. 4. After upgrade, verify the version matches the fixed release (6.3.16 or 6.4.2 or later).
  5. 5. Confirm the XSS vulnerability is resolved by testing that crafted GET parameters in login/error handlers are no longer executed.
Caveat Review FortiWeb release notes for version-specific changes; major version jumps may require configuration adjustments

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

Fix this in Fortiweb Scoped from the published advisory
  • Consultation2.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
16.0 hours of engineering $2,800
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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-2021-36188 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
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