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WicketApplication · Apache

CVE-2021-23937

HIGH · 7.5 CVSS v3.1 Published 2021-05-25
Fix available
A fix is available. Upgrade to after 9.2.0 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable 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 DNS proxy and possible amplification attack vulnerability in WebClientInfo of Apache Wicket allows an attacker to trigger arbitrary DNS lookups from the server when the X-Forwarded-For header is not properly sanitized. This DNS lookup can be engineered to overload an internal DNS server or to slow down request processing of the Apache Wicket application causing a possible denial of service on either the internal infrastructure or the web application itself. This issue affects Apache Wicket Apache Wicket 9.x version 9.2.0 and prior versions; Apache Wicket 8.x version 8.11.0 and prior versions; Apache Wicket 7.x version 7.17.0 and prior versions and Apache Wicket 6.x version 6.2.0 and later versions.

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

Apache Wicket's WebClientInfo component does not properly sanitize the X-Forwarded-For HTTP header before using it in DNS lookups. Attackers can manipulate this header to cause the server to perform arbitrary DNS queries, potentially overloading internal DNS servers or causing denial of service through amplified traffic and slow request processing.

MitigationSanitize and validate the X-Forwarded-For header before using it in DNS operations, implement rate limiting on DNS lookups, and upgrade to patched Apache Wicket versions (6.24.0+, 7.18.0+, 8.12.0+, or 9.3.0+).

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
WicketApplication
Affected:>= 6.0.0, <= 6.2.0>= 7.0.0, <= 7.17.0>= 8.0.0, <= 8.11.0>= 9.0.0, <= 9.2.0

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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

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. Identify the Apache Wicket version in use
    Locate the wicket-core JAR file in your application deployment (check WEB-INF/lib directory or build dependencies) and note its version, or run a dependency command like 'mvn dependency:list' for Maven projects
    Affected if The installed version falls within 6.0.0-6.2.0, 7.0.0-7.17.0, 8.0.0-8.11.0, or 9.0.0-9.2.0
  2. Determine if WebClientInfo is used in your application
    Search your codebase for imports of org.apache.wicket.WebClientInfo or usages of WebClientInfo class in Java source files, or check application logs for WebClientInfo instantiation
    Affected if WebClientInfo is actively used in the application code
  3. Check if the application processes X-Forwarded-For headers
    Inspect your application's web server or proxy configuration (e.g., Apache HTTP server, Nginx, load balancer) to confirm X-Forwarded-For header handling is enabled, or review request handling code for getHeader("X-Forwarded-For") calls
    Affected if X-Forwarded-For headers are being processed and passed through to the application
  4. Verify DNS lookup behavior with WebClientInfo
    Send a test request with a manipulated X-Forwarded-For header (e.g., X-Forwarded-For: evil.example.com) and monitor DNS queries originating from the server using network capture (tcpdump) or DNS server logs
    Affected if The server performs DNS lookups on arbitrary values from the X-Forwarded-For header without validation

You are affected if your Apache Wicket version is within the affected ranges AND WebClientInfo is being used while processing X-Forwarded-For headers from proxied requests.

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.

From vendor data
Upgrade available Upgrade to a release after 9.2.0
Interim mitigation

Sanitize and validate the X-Forwarded-For header before using it in DNS operations, implement rate limiting on DNS lookups, and upgrade to patched Apache Wicket versions (6.24.0+, 7.18.0+, 8.12.0+, or 9.3.0+).

Fix this in Wicket Scoped from the published advisory
  • Consultation3.0 h
  • Implementation6.0 h
  • Testing3.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,490
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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-2021-23937 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
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  • Version or environment caveats, and links to real fixes
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