CVE-2026-84177 Vulnerability Analysis & Exploit Details

CVE-2026-84177 Vulnerability Summary

CVE-2026-84177: Incorrect behavior order in Apache Wicket: a file path is validated before the framework appends the attributes that complete it. org.apache.wicket.request.resource.PackageResource asks the configured package resource guard about a path built from the scope class' package and the file name in the request URL, and then hands that same path to the resource stream locator together with a style, a variation and a locale. Those three attributes are decoded from the name of the first query parameter and never appear in the string the guard was given. org.apache.wicket.core.util.resource.locator.ResourceNameIterator appends them to that path, each preceded by an underscore, in the order variation, style, locale, before the file extension, so the file that is opened is not the file the guard approved. org.apache.wicket.markup.html.PackageResourceGuard decides whether an HTML file is a component's markup template by looking for a class file of the same name beside it, stripping one underscore-delimited suffix at a time as it goes. HTML is on the default allow list, so that check is the only thing separating a static HTML file, which may be served, from a markup template, which may not. Asked about the name of a template, the guard refuses it correctly. Asked about a shorter name for which no class exists, it accepts, and a style supplied in the URL then completes that name into the markup template of a component class, which is written to the response. An application is affected if the simple name of any of its component classes contains an underscore and no shorter part of that name is itself a class, such as Report_v2 or Wizard_Step1; an application with no such class name is not affected. No unusual deployment, packaging or configuration is required, and running in deployment rather than development mode does not prevent it. Java naming conventions discourage underscores in class names and no module Wicket ships has one, so no framework markup is exposed; what an application exposes this way is its own. A component whose class name has no underscore is not reachable, and neither is its localized or styled markup, because the guard finds the class file under the base name and refuses the request. The attributes cannot change the file extension and cannot leave the component's package, so nothing beyond HTML files in that package is reachable. Access is read-only, and what is disclosed is developer-authored template content: component structure, developer comments, markup that is rendered only under some conditions, inline script, and the endpoints a template names. No user data, credential or session material is reachable this way. An attacker has to name a class in the target package and the component itself, and Wicket writes fully qualified class names into the URL of every package resource it renders. This issue affects Apache Wicket: from 8.0.0 through 8.19.0, from 9.0.0 through 9.24.0, from 10.0.0 through 10.11.0. Users of Apache Wicket 7.x or older, which are no longer supported, should upgrade to a supported version. Users are recommended to upgrade to version 8.20.0, 9.25.0 or 10.12.0, which fix the issue.

CVE-2026-84177 References

External References

• https://lists.apache.org/thread.html/hy089v60t5v36skpnbry96vr2427lw0o

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• Using Leading 'Ghost' Character Sequences to Bypass Input Filters CAPEC-3 Some APIs will strip certain leading characters from a string of parameters. An adversary can intentionally introduce leading "ghost" characters (extra characters that don't affect the validity of the request at the API layer) that enable the input to pass the filters and therefore process the adversary's input. This occurs when the targeted API will accept input data in several syntactic forms and interpret it in the equivalent semantic way, while the filter does not take into account the full spectrum of the syntactic forms acceptable to the targeted API.
• Exploiting Multiple Input Interpretation Layers CAPEC-43 An attacker supplies the target software with input data that contains sequences of special characters designed to bypass input validation logic. This exploit relies on the target making multiples passes over the input data and processing a "layer" of special characters with each pass. In this manner, the attacker can disguise input that would otherwise be rejected as invalid by concealing it with layers of special/escape characters that are stripped off by subsequent processing steps. The goal is to first discover cases where the input validation layer executes before one or more parsing layers. That is, user input may go through the following logic in an application: <parser1> --> <input validator> --> <parser2>. In such cases, the attacker will need to provide input that will pass through the input validator, but after passing through parser2, will be converted into something that the input validator was supposed to stop.
• Using Unicode Encoding to Bypass Validation Logic CAPEC-71 An attacker may provide a Unicode string to a system component that is not Unicode aware and use that to circumvent the filter or cause the classifying mechanism to fail to properly understanding the request. That may allow the attacker to slip malicious data past the content filter and/or possibly cause the application to route the request incorrectly.

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