Description

A flaw was found in the Qute template engine, which is used by Quarkus to generate dynamic content like HTML pages or emails. The issue exists in the component responsible for looking up data values (ReflectionValueResolver), which fails to properly block access to sensitive Java internal functions when processing certain data types like Enums. An attacker who can provide or influence the template text can exploit this bypass to take control of the server by executing unauthorized commands.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.8",
  "pubDate": "2026-08-31T13:17:20.753Z",
  "pubdate": "2026-08-31T13:17:20.753Z",
  "executiveSummary": "A critical security vulnerability exists within the Qute template engine, specifically affecting the ReflectionValueResolver component used by Quarkus. The flaw involves an improper neutralization of access control mechanisms when handling sensitive Java types, such as Enums. This vulnerability allows an attacker capable of influencing template content to bypass existing security restrictions and access restricted Java internal functions. The successful exploitation of this flaw leads to Remote Code Execution (RCE), granting the attacker the ability to execute unauthorized commands with the privileges of the application process. This vulnerability poses a severe risk to confidentiality, integrity, and availability, as it effectively enables full system compromise if an attacker can inject malicious templates into the application's processing pipeline.",
  "technicalDetails": "The vulnerability resides in the ReflectionValueResolver, which is responsible for resolving variables and method calls within Qute templates. The core issue stems from a failure to strictly enforce blocklists or allowlists when the engine evaluates expressions involving Java Enums. While the Qute engine implements security safeguards intended to prevent access to sensitive internal Java APIs, the implementation within the ReflectionValueResolver fails to adequately restrict these access paths for specific data structures.\nThe attack flow begins when an attacker provides or influences template text processed by the Qute engine. By crafting a template expression that targets Enum types or specific objects, the attacker can leverage the flawed resolver logic to traverse the object graph into restricted Java internal classes and methods that should have been prohibited. Because the engine does not correctly validate these lookups, the attacker can invoke methods capable of performing reflection-based operations or executing system-level functions.\nExploitation involves the construction of a malicious payload that utilizes Qute syntax to invoke underlying Java methods that the engine incorrectly identifies as safe or neglects to check. By chaining these unauthorized method calls, an attacker can manipulate the application runtime. The process effectively bypasses the sandbox constraints imposed by the template engine, allowing for the instantiation of arbitrary classes or the execution of methods that trigger system commands.\nThis vulnerability effectively elevates the privileges of the template-processing context to those of the application server. The post-exploitation impact is total system compromise; an attacker can retrieve sensitive information, modify data, or execute arbitrary shell commands. This flaw is particularly dangerous in environments where template generation is exposed to untrusted user input, such as web applications generating dynamic emails or personalized HTML content. As the flaw exists within the core resolution logic, any version of Quarkus utilizing the vulnerable ReflectionValueResolver implementation is susceptible. No authentication is required if the entry point for template injection is publicly accessible, making it a critical vector for network-based attacks against the application."
}