Improper neutralization of input during web page generation in Apache Wicket. Apache Wicket generates JavaScript that refers to the elements it renders, and writes into that JavaScript two values it derives itself: a component's markup id, and the input name of a form component, which is built from component ids. Both are placed inside single-quoted JavaScript string literals without being escaped for that context, so a value containing a single quote or a backslash ends the literal, and what follows is parsed as script and runs in the application's origin when the page loads. A markup id is the value passed to org.apache.wicket.Component#setMarkupId(String), or the id attribute written in the component's markup, or an id Wicket generates, in that order. The first two are supplied by the application in an HTML context, where both characters are legal and where Wicket escapes them correctly when it writes the same value into the id attribute of the element; a generated id cannot contain either. An input name is derived from the ids of the components between the form and the form component, and a component id was rejected only for ':' and '~'. In org.apache.wicket:wicket-core on 9.x and 10.x, org.apache.wicket.markup.head.OnEventHeaderItem#forMarkupId(String, String, CharSequence) quotes the id it is given into a Wicket.Event.add call, and components in both wicket-core and wicket-extensions reach it through #forComponent(Component, String, CharSequence). On every affected version, org.apache.wicket.markup.html.form.Form writes its markup id and the id of its hidden-fields container into such literals, org.apache.wicket.markup.html.form.FormComponentUpdatingBehavior writes an input name, and org.apache.wicket.markup.html.form.upload.MultiFileUploadField writes two markup ids and an input name. On 8.x, Form also writes an input name into the action of a submitting link, and on 8.x and 9.x Form#appendDefaultButtonField writes an input name into a name attribute with no escaping at all, so a value containing a double quote escapes the attribute into markup. org.apache.wicket:wicket-extensions is affected in its own right and not only through wicket-core: AjaxEditableLabel, AjaxIndicatorAppender, AjaxDisableComponentListener, UploadProgressBar, KittenCaptchaPanel, Palette, FilterForm and, on 9.x and 10.x, TrapFocusBehavior and AjaxListPanel each build their own JavaScript containing a markup id. An application is affected where a markup id or a component id carries one of those characters. Wicket does not put one there itself, so the value comes from the application: an id set on a component, an id attribute in a template, or a component id derived from data. None of those is a JavaScript context from the application's point of view. The Content-Security-Policy that Apache Wicket 9.x and 10.x send by default does not prevent this. The generated script is written into a script element carrying the per-response nonce, so the injected code is part of a script the policy admits. The fixed versions check an id where it enters instead of escaping each place it is written. A component id and a markup id may no longer contain a quote, a backquote, a backslash, braces, angle brackets, a semicolon, an ampersand or a control character, and a markup id may not contain parentheses or square brackets either; a component constructed with such an id, or given such a markup id, fails with an exception. 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.