Summary
Authorization Before Parsing and Canonicalization in jetty
Release 9.4.37 introduced a more precise implementation of RFC3986 with regards to URI decoding, together with some new compliance modes to optionally allow support of some URI that may have ambiguous interpretation within the Servlet specified API methods behaviours. The default mode allowed % encoded . characters to be excluded for URI normalisation, which is correct by the RFC, but is not assumed by common Servlet implementations. 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. Workarounds found by HttpCompliance mode RFC7230_NO_AMBIGUOUS_URIS can be enabled by updating start.d/http.ini to include: jetty.http.compliance=RFC7230_NO_AMBIGUOUS_URIS.
Impact
The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions. Typical impact: unauthorized data access or execution of privileged operations.
CVE-2021-28164 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (9.4.39); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is CVE-2021-28164? CVE-2021-28164 is a medium-severity incorrect authorization vulnerability in org.eclipse.jetty:jetty-webapp (maven), affecting versions >= 9.4.37, < 9.4.39. It is fixed in 9.4.39. The application does not correctly enforce access controls, allowing a principal to access resources or operations beyond their granted permissions.
- How severe is CVE-2021-28164? CVE-2021-28164 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.eclipse.jetty:jetty-webapp are affected by CVE-2021-28164? org.eclipse.jetty:jetty-webapp (maven) versions >= 9.4.37, < 9.4.39 is affected.
- Is there a fix for CVE-2021-28164? Yes. CVE-2021-28164 is fixed in 9.4.39. Upgrade to this version or later.
- Is CVE-2021-28164 exploitable, and should I be worried? Whether CVE-2021-28164 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-28164 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-28164? Upgrade
org.eclipse.jetty:jetty-webappto 9.4.39 or later.