KeycloakApplication · Redhat
CVE-2021-20323
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 · uneditedA POST based reflected Cross Site Scripting vulnerability on has been identified in Keycloak.
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 confidenceA POST-based reflected Cross-Site Scripting (XSS) vulnerability exists in Keycloak. The vulnerability allows attackers to inject malicious scripts through POST parameters that are reflected back in the server's response without proper sanitization, potentially leading to session hijacking or credential theft.
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
KeycloakApplication
< 17.0.0CVSS 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 checksWork through these to decide whether this CVE applies to you.
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Identify Keycloak versionCheck the installed Keycloak version by reviewing the server startup logs, the 'product.version' in /opt/keycloak/bin/kc.sh --version (if CLI accessible), or the pom.xml/build.gradle if source is availableAffected if The installed version is below 17.0.0 (e.g., 16.x, 15.x, 14.x, etc.)
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Confirm admin console is accessibleAccess the Keycloak admin console at /auth/admin/ or /admin/ and verify the login page loads without errorsAffected if The admin console is reachable and running on an affected version
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Review custom themes for unsafe outputInspect any custom themes in the themes/ directory. Look for .ftl (FreeMarker) templates that directly render request parameters without using <@c.out> or equivalent escaping macrosAffected if Custom themes render POST parameters directly in responses without proper encoding
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Check for reverse proxy configurationExamine any reverse proxy (nginx, Apache, HAProxy) in front of Keycloak that might normalize or pass through POST parameters without sanitizationAffected if A reverse proxy passes POST parameters to Keycloak without filtering malicious input patterns
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Test for parameter reflectionSubmit a harmless test string like '<script>test</script>' in a POST request to common Keycloak endpoints (login, registration, account, admin). Inspect the HTTP response to see if the raw string appears unescapedAffected if The test string appears in the response body as '<script>test</script>' rather than '<script>test</script>'
The environment is affected if Keycloak version is below 17.0.0 AND POST parameters are reflected in server responses without HTML encoding.
Generated from the published advisory. Verify against your own configuration.
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 · scoped17.0.0
Implement robust input validation and output encoding for all user-supplied POST parameters. Apply context-appropriate escaping when rendering user input in HTML responses.
Keycloak 17.0.0
- Download Keycloak 17.0.0 or later from the official Keycloak releases page
- Review the Keycloak 17.0.0 migration guide for breaking changes from your current version
- Backup your existing Keycloak database and configuration
- Stop the current Keycloak instance
- Install Keycloak 17.0.0 in your target environment
- Run the database migration scripts if required by your database type
- Start the new Keycloak instance and verify all realms and clients are functioning correctly
- Test the application integrations to ensure authentication flows work properly
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Keycloak
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-20323 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-20323 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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