CVE-2026-66296 Reflected XSS in oaskit's default HTML error handler
Reflected XSS in oaskit's default HTML error handler allows attackers to execute scripts in the victim's browser via crafted links, potentially stealing sessions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-66296?
CVE-2026-66296 is a medium-severity cross-site scripting vulnerability in lud oaskit, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in lud oaskit allows reflected cross-site scripting via the default HTML error handler.
Oaskit.ErrorHandler.Default.format_reason/4 and Oaskit.ErrorHandler.Default.reason_to_html/1 in lib/oaskit/error_handler/default.ex render request-validation failures as an HTML page whenever the request's Accept header contains html, interpolating request-controlled strings into that page without HTML escaping. The unescaped values are object keys taken from a request body or from an object or deepObject query parameter, which appear in the JSON Schema error's instance path when a schema rejects them (for example under additionalProperties: false), and the raw Content-Type header, reflected in unsupported-media-type errors when it fails to parse.
Because browsers send Accept: text/html on ordinary top-level navigation, a crafted GET link is sufficient to trigger the error page; no form submission, custom Content-Type, or attacker-controlled script on the victim's side is required. A payload such as filter[</code></h2><script>alert(document.domain)</script>]=x terminates the enclosing markup and the injected script executes in the origin of the application using oaskit, giving it access to that origin's cookies, session, and same-origin responses.
Both HTML error rendering and the vulnerable handler are enabled by default: Oaskit.Plugs.ValidateRequest defaults :html_errors to true and :error_handler to Oaskit.ErrorHandler.Default, so applications following the documented usage are affected without any opt-in.
This issue affects oaskit: from 0.1.0 before 0.14.1.
Weakness: CWE-79
Which versions are affected by CVE-2026-66296?
1 open source package ship an affected version, including oaskit. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
oaskit Hex | From 0.1.0 | 0.14.1 |
Products include Lud Oaskit.
How do I fix CVE-2026-66296?
Upgrade oaskit to 0.14.1 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-66296 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-66296 exists.
Sources
Also known as EEF-CVE-2026-66296, GHSA-5rgx-mcq5-r7wv, GHSA-h7xw-x8wr-xpcc.