CVE-2021-23937

DNS proxy and possible amplification attack

Description

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.

Remediation

Workaround:

  • Sanitize the X-Forwarded-For header by running an Apache Wicket application behind a reverse HTTP proxy. This proxy should put the client IP address in the X-Forwarded-For header and not pass through the contents of the header as received by the client.

Category

7.5
CVSS
Severity: High
CVSS 3.1 •
CVSS 2.0 •
EPSS 6.87% Top 10%
Vendor Advisory apache.org
Affected: Apache Software Foundation Apache Wicket
Published at:
Updated at:

References

Link Tags
https://lists.apache.org/thread.html/rc2ef22f90793e158cef65a7e370cdbca023c499d1403d65feeca870d%40%3Cusers.wicket.apache.org%3E mailing list release notes vendor advisory
https://lists.apache.org/thread.html/r127c0c1f3cb71e5bc619ad1e4b898b97c49758d1f20a54042966473e%40%3Cannounce.wicket.apache.org%3E mailing list
https://lists.apache.org/thread.html/r127c0c1f3cb71e5bc619ad1e4b898b97c49758d1f20a54042966473e%40%3Cusers.wicket.apache.org%3E mailing list
https://lists.apache.org/thread.html/r8ccbd91b56ebf045d151bd4282bfeea7842a0698a0b76118fca8fe78%40%3Cdev.wicket.apache.org%3E mailing list

Frequently Asked Questions

What is the severity of CVE-2021-23937?
CVE-2021-23937 has been scored as a high severity vulnerability.
How to fix CVE-2021-23937?
As a workaround for remediating CVE-2021-23937: Sanitize the X-Forwarded-For header by running an Apache Wicket application behind a reverse HTTP proxy. This proxy should put the client IP address in the X-Forwarded-For header and not pass through the contents of the header as received by the client.
Is CVE-2021-23937 being actively exploited in the wild?
It is possible that CVE-2021-23937 is being exploited or will be exploited in a near future based on public information. According to its EPSS score, there is a ~7% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-23937?
CVE-2021-23937 affects Apache Software Foundation Apache Wicket.
This platform uses data from the NIST NVD, MITRE CVE, MITRE CWE, First.org and CISA KEV but is not endorsed or certified by these entities. CVE is a registred trademark of the MITRE Corporation and the authoritative source of CVE content is MITRE's CVE web site. CWE is a registred trademark of the MITRE Corporation and the authoritative source of CWE content is MITRE's CWE web site.
© 2025 Under My Watch. All Rights Reserved.