CVE-2026-66296
Improper Neutralization of Input During Web Page Generation (XSS) vulnerability in lud oaskit allows reflected cross-site scripting via the default HTML error handler.
Does this matter?
Lower severity and a low EPSS score (0.24%). Track it; it rarely justifies an emergency change on its own.
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.
- CVSS 4.0
- 5.1 MEDIUMCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.24% probability · 16th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-79
- Affected
- lud/oaskit
- Source
- 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
References
- https://cna.erlef.org/cves/CVE-2026-66296.htmlPatch, Third Party Advisory
- https://github.com/lud/oaskit/commit/b70c6b2eaf0b11bdd0bbb21b8a87dbb3d46918a1Patch
- https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpccExploit, Vendor Advisory
- https://osv.dev/vulnerability/EEF-CVE-2026-66296Patch, Third Party Advisory
- https://github.com/lud/oaskit/security/advisories/GHSA-h7xw-x8wr-xpccExploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.