Summary
Jetty Utility Servlets ConcatServlet Double Decoding Information Disclosure Vulnerability
Requests to the ConcatServlet and WelcomeFilter are able to access protected resources within the WEB-INF directory. For example a request to the ConcatServlet with a URI of /concat?/%2557EB-INF/web.xml can retrieve the web.xml file. This can reveal sensitive information regarding the implementation of a web application.
This occurs because both ConcatServlet and WelcomeFilter decode the supplied path to verify it is not within the WEB-INF or META-INF directories. It then uses this decoded path to call RequestDispatcher which will also do decoding of the path. This double decoding allows paths with a doubly encoded WEB-INF to bypass this security check.
Workarounds
If you cannot update to the latest version of Jetty, you can instead deploy your own version of the ConcatServlet and/or the WelcomeFilter by using the code from the latest version of Jetty.
Impact
This affects all versions of ConcatServlet and WelcomeFilter in versions before 9.4.41, 10.0.3 and 11.0.3.
CVE-2021-28169 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 (9.4.41, 10.0.3, 11.0.3); 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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org.eclipse.jetty:jetty-servlets to 9.4.41 or later; org.eclipse.jetty:jetty-servlets to 10.0.3 or later; org.eclipse.jetty:jetty-servlets to 11.0.3 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2021-28169? CVE-2021-28169 is a medium-severity security vulnerability in org.eclipse.jetty:jetty-servlets (maven), affecting versions <= 9.4.40. It is fixed in 9.4.41, 10.0.3, 11.0.3.
- How severe is CVE-2021-28169? CVE-2021-28169 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-servlets are affected by CVE-2021-28169? org.eclipse.jetty:jetty-servlets (maven) versions <= 9.4.40 is affected.
- Is there a fix for CVE-2021-28169? Yes. CVE-2021-28169 is fixed in 9.4.41, 10.0.3, 11.0.3. Upgrade to this version or later.
- Is CVE-2021-28169 exploitable, and should I be worried? Whether CVE-2021-28169 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-2021-28169 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-2021-28169?
- Upgrade
org.eclipse.jetty:jetty-servletsto 9.4.41 or later - Upgrade
org.eclipse.jetty:jetty-servletsto 10.0.3 or later - Upgrade
org.eclipse.jetty:jetty-servletsto 11.0.3 or later
- Upgrade