How severe is CVE-2021-28164?

CVE-2021-28164 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-28164?

CVE-2021-28164 affects the following packages: org.eclipse.jetty:jetty-webapp (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-28164?

Update org.eclipse.jetty:jetty-webapp to 9.4.39 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-28164 is resolved across your whole dependency graph.

How do I detect CVE-2021-28164 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.eclipse.jetty:jetty-webapp. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2021-28164 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2021-28164?

O3 pinpoints whether CVE-2021-28164 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2021-28164 actively exploited in the wild?

Yes. There are 3 known exploit references for CVE-2021-28164, including 1 documented proof-of-concept exploit on Exploit-DB and 2 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-28164?

CVE-2021-28164 has an EPSS (Exploit Prediction Scoring System) score of 82.4%, placing it in the 100th 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. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

What type of vulnerability is CVE-2021-28164?

CVE-2021-28164 is classified as Information Exposure (CWE-200), CWE-551 (CWE-551). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

Is there exploit tooling available for CVE-2021-28164?

A Nuclei detection template exists for CVE-2021-28164, meaning automated scanners can fingerprint it. 2 Metasploit modules reference CVE-2021-28164, which lowers the barrier to weaponization. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-28164 published, and has it been updated?

CVE-2021-28164 was published on April 1, 2021 and was last updated on July 8, 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-2021-28164: Authorization Before Parsing and Canonicalizati…

EPSS Exploitation Probability

via FIRST.org ↗

82.4%probability of exploitation in next 30 days

Very High Risk100th percentile0.00%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

☕org.eclipse.jetty:jetty-webapp

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

In Eclipse Jetty 9.4.37.v20210219 to 9.4.38.v20210224, the default compliance mode allows requests with URIs that contain %2e or %2e%2e segments to access protected resources within the WEB-INF directory. For example a request to /context/%2e/WEB-INF/web.xml can retrieve the web.xml file. This can reveal sensitive information regarding the implementation of a web application.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`org.eclipse.jetty:jetty-webapp`	≥ 9.4.37&&< 9.4.39	9.4.39

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.eclipse.jetty:jetty-webapp. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.eclipse.jetty:jetty-webapp to 9.4.39 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-28164 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-28164 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2021-28164. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

In Eclipse Jetty 9.4.37.v20210219 to 9.4.38.v20210224, the default compliance mode allows requests with URIs that contain %2e or %2e%2e segments to access protected resources within the WEB-INF directory. For example a request to /context/%2e/WEB-INF/web.xml can retrieve the web.xml file. This can reveal sensitive information regarding the implementation of a web application.

O3 Security · Impact-Aware SCA

Is CVE-2021-28164 in your dependencies?

O3 detects CVE-2021-28164 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works

CVE-2021-28164