CVE-2026-93432 in Quarkus
Summary
by MITRE • 09/18/2026
A flaw was found in the Quarkus Qute template engine. When the {#eval} section helper processes a sub-template, it fails to pass the parent template's content type information. This bypasses standard escaping mechanisms, allowing untrusted data to be output as raw, unescaped text. This vulnerability can lead to Cross-Site Scripting (XSS) and JSON Injection, potentially allowing a remote attacker to execute arbitrary code in a user's browser or manipulate data.
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Analysis
by VulDB Data Team • 09/18/2026
The Quarkus Qute template engine contains a critical security flaw within its {#eval} section helper mechanism that compromises the integrity of content type handling during sub-template rendering. This vulnerability stems from an implementation oversight where the parent template’s declared content type is not correctly propagated to child or sub-templates when they are processed through this specific helper. In standard web application architecture, templates rely on strict context awareness to determine how data should be serialized and escaped before being sent to the client. By failing to pass this crucial metadata, the engine loses the ability to apply appropriate sanitization rules tailored to the target format, such as HTML or JSON. This breakdown in context propagation creates a direct path for untrusted user input to bypass standard escaping mechanisms that would normally neutralize malicious payloads embedded within dynamic data fields.
The operational impact of this flaw is severe, primarily manifesting as Cross-Site Scripting and JSON Injection vulnerabilities. When the content type information is missing, the template engine treats all output as plain text or applies default escaping rules that are insufficient for specific contexts like HTML attributes or script blocks. Consequently, an attacker who can influence the data passed through a {#eval} section helper can inject malicious scripts into web pages viewed by other users. In a browser environment, this allows for arbitrary code execution, session hijacking, and defacement of application interfaces. Furthermore, if the affected endpoint serves JSON responses, the lack of proper escaping enables JSON Injection attacks. This technique can be used to manipulate client-side JavaScript objects or exfiltrate sensitive data by exploiting how browsers parse malformed JSON structures that contain executable script tags within string values.
From a classification perspective, this vulnerability aligns with CWE-79, which covers Improper Neutralization of Input During Web Page Generation commonly known as Cross-Site Scripting. The specific mechanism involves the failure to enforce output encoding based on context, which is also related to CWE-80 and CWE-116 depending on whether the injection occurs in HTML or other contexts like JSON. In terms of offensive security frameworks, this flaw facilitates techniques documented under MITRE ATT&CK ID T1059, specifically Command Line Interface Execution via browser-based scripts, as well as data exfiltration methods associated with client-side attacks. The root cause is a logical error in the template engine’s state management rather than a simple buffer overflow or memory corruption issue, making it particularly insidious because standard input validation checks may pass while the output rendering phase remains vulnerable due to missing context metadata.
Mitigation strategies must focus on ensuring that content type information is strictly preserved and enforced throughout the entire template processing pipeline. Developers should update the Quarkus Qute library to a patched version where this propagation bug has been resolved, ensuring that sub-templates inherit the correct escaping rules from their parent contexts. In environments where an immediate patch is not feasible, application-level mitigations include implementing strict output encoding for all dynamic content before it reaches the template engine or disabling the use of the {#eval} helper with untrusted data sources entirely. Additionally, deploying a Web Application Firewall configured to detect and block common XSS payloads in JSON responses can provide a layer of defense-in-depth while long-term architectural fixes are implemented. Regular security audits focusing on dynamic content rendering paths are recommended to identify similar context-awareness failures in other template engines or custom serialization logic within the application stack.