DNS based denial of service in Apache Wicket

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

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

EPSS

• CVE-2021-23937: 4.26% estimated exploitation activity in the next 30 days; percentile 91.08 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

24 May 2022, 19:03 UTC

Last modified by the source

8 Aug 2023, 19:55 UTC

Source last checked

26 Oct 2026, 16:11 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hmhg-95wh-r699

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# Patch Next advisory brief: CVE-2021-23937

Advisory: DNS based denial of service in Apache Wicket
IDs: CVE-2021-23937, GHSA-hmhg-95wh-r699
Record: https://patchnext.com/advisories/cve-2021-23937 (revision 1, source checked 26 Oct 2026, 16:11 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.apache.wicket:wicket-core 9.3.0, 8.12.0, 7.18.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.apache.wicket:wicket-core: affected >= 9.0.0, < 9.3.0; >= 8.0.0, < 8.12.0; < 7.18.0; fixed in 7.18.0, 9.3.0, 8.12.0

## Suggested inspection (read-only)
- Maven org.apache.wicket:wicket-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.apache.wicket:wicket-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hmhg-95wh-r699 (GitHub-reviewed advisory GHSA-hmhg-95wh-r699 lists affected ranges: Maven org.apache.wicket:wicket-core >=9.0.0 =8.0.0 =0 <7.18.0)

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