How severe is CVE-2021-23937?

CVE-2021-23937 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-23937?

CVE-2021-23937 affects the following packages: org.apache.wicket:wicket-core (Maven), org.apache.wicket:wicket-core (Maven), org.apache.wicket:wicket-core (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-23937?

Update org.apache.wicket:wicket-core to 9.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23937 is resolved across your whole dependency graph.

How do I detect CVE-2021-23937 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.wicket:wicket-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-23937 if there is no patch (or I can't update yet)?

Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Is CVE-2021-23937 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-23937 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-23937?

CVE-2021-23937 has an EPSS (Exploit Prediction Scoring System) score of 4.3%, placing it in the 91th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-23937?

CVE-2021-23937 is classified as Information Exposure (CWE-200). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-23937 published, and has it been updated?

CVE-2021-23937 was published on May 25, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2021-23937: wicket-core DoS

EPSS Exploitation Probability

via FIRST.org ↗

4.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs91th percentile — riskier than 91% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

3 pkgs affected

☕org.apache.wicket:wicket-core☕org.apache.wicket:wicket-core☕org.apache.wicket:wicket-core

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.apache.wicket:wicket-core`	≥ 9.0.0&&< 9.3.0	9.3.0`org.apache.wicket:wicket-core:9.3.0`
☕Maven	`org.apache.wicket:wicket-core`	≥ 8.0.0&&< 8.12.0	8.12.0`org.apache.wicket:wicket-core:8.12.0`
☕Maven	`org.apache.wicket:wicket-core`	all versions	7.18.0`org.apache.wicket:wicket-core:7.18.0`

Affected Products

1 product · 4 configurations

Application

wicketapache

≥ 9.0.0 && ≤ 9.2.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.wicket:wicket-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update org.apache.wicket:wicket-core to 9.3.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23937 is resolved across your whole dependency graph.
Workarounds
Assume what was exposed is already known: rotate any credential, token or key that the affected component could return, restrict the endpoint to callers that genuinely need it, and strip sensitive fields from responses and error output at the boundary rather than relying on the client not to read them.

Frequently Asked Questions

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

O3 Security · Impact-Aware SCA

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CVE-2021-23937 — wicket-core

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored