CVE-2026-73101 in Juneau
Summary
by MITRE • 11/05/2026
Generation of Error Message Containing Sensitive Information vulnerability in Apache Juneau.
The REST server sends the internal exception class and message to clients in a "Thrown" response header on every error response, and can include internal exception messages in the error body, even when stack-trace rendering is disabled. This reveals implementation details to remote clients.
This issue affects Apache Juneau: through 9.2.0.
Users are recommended to upgrade to version 9.2.1, which fixes the issue.
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Analysis
by VulDB Data Team • 11/05/2026
The vulnerability identified in Apache Juneau constitutes a significant information disclosure flaw rooted in improper error handling mechanisms within the REST server implementation. This specific weakness allows an attacker or any remote client interacting with the service to extract sensitive internal details that should remain hidden from external entities. The core of the issue lies in how the framework constructs HTTP responses when an exception occurs during request processing. Instead of returning a generic, sanitized error message suitable for public consumption, the server actively includes detailed technical data about the underlying failure. This behavior violates fundamental security principles regarding the separation of internal system states and external user interfaces, creating a vector for reconnaissance that can facilitate further attacks against the application infrastructure.
Technically, the flaw manifests through two primary channels within the HTTP response structure. First, the framework populates a custom header named "Thrown" with information derived from the internal exception class name and its associated message string. This occurs on every error response generated by the server, regardless of whether stack trace rendering is explicitly disabled in the configuration settings. Second, beyond headers, the vulnerability extends to the body of the HTTP response itself, where implementation-specific details may be embedded within the serialized error payload. By exposing these internal exception messages and class names, the application inadvertently reveals insights into its codebase structure, dependency versions, and potentially sensitive data processing logic that was involved in triggering the error. This level of detail provides attackers with a clear map of the technology stack and potential weak points to exploit.
The operational impact of this vulnerability is primarily centered around enabling advanced reconnaissance activities by malicious actors. When an attacker triggers an error condition, whether intentionally through malformed requests or accidentally via legitimate but edge-case inputs, they receive detailed feedback about what went wrong inside the server. This information can be used to identify specific libraries in use, infer database query structures if SQL errors are exposed, or detect misconfigurations that could lead to more severe vulnerabilities such as remote code execution or unauthorized data access. The persistence of this behavior even when stack traces are disabled indicates a fundamental oversight in the error handling pipeline, meaning that standard security configurations intended to hide technical details fail to mitigate this specific exposure vector effectively.
This vulnerability aligns with CWE-209, which describes the generation of an error message that includes sensitive information for its owner or users, and is also related to CWE-200, concerning the exposure of sensitive information to an unauthorized actor. In terms of offensive security frameworks, this behavior supports the ATT&CK technique T1589, specifically Gather Victim Identity Information, as it allows adversaries to gather details about the victim's environment including software versions and internal architecture. Such intelligence gathering is often a precursor to more destructive attacks, making the remediation of this issue critical for maintaining defense-in-depth strategies.
To mitigate this risk, organizations running affected versions of Apache Juneau must upgrade immediately to version 9.2.1 or later, where the developers have addressed these information leakage issues by ensuring that error responses are sanitized and do not expose internal exception details in headers or bodies. For environments unable to patch immediately due to dependency constraints, implementing a reverse proxy such as Nginx or Apache HTTP Server can provide an additional layer of protection. By configuring the proxy to intercept 5xx errors from the backend application and replace them with generic error pages, organizations can prevent sensitive internal messages from reaching the client side. Additionally, developers should review custom exception handlers within their applications to ensure that any manual construction of error responses adheres to strict sanitization protocols, stripping out stack traces, class names, and raw message contents before transmission over the network.