CVE-2026-93710 in Dancer2
Summary
by MITRE • 09/22/2026
Dancer2 versions from 2.0.0 before 2.2.0 for Perl dispatch a route that a dying hook refused when the exception handler halts the response in compile_hooks.
A hook that dies fires core.app.hook_exception, then calls cleanup unless the failing hook is the exception handler. A handler that halts does not stop that cleanup, which discards the request, response and session the dispatcher has yet to read, so the refused route runs.
The handler has to halt the response object by calling its halt method or setting is_halted: the halt keyword unwinds through with_return before cleanup runs.
A check in a before hook is not enforced: the caller gets the refusal, while the route body runs and its writes land.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified within Dancer2 versions ranging from 2.0.0 up to but excluding 2.2.0 represents a critical logic flaw in the framework's request lifecycle management, specifically concerning how hooks interact with exception handling and route dispatching mechanisms. This issue stems from an inconsistency in how the application handles state transitions when a hook fails or explicitly halts execution. In a typical Dancer2 workflow, the dispatcher processes incoming requests by executing various hooks such as before, after, and error handlers to manage pre-processing logic, post-response modifications, and exception management respectively. The core of this vulnerability lies in the interaction between dying hooks, which trigger exceptions, and the cleanup routines that are invoked during these events. When a hook dies or throws an unhandled exception, it triggers the app.hook_exception event, followed by a call to the cleanup subroutine unless the failing hook is itself the designated exception handler. This design assumes that halting execution at this stage will prevent further processing of the current request context.
However, the flaw manifests when an exception handler explicitly attempts to halt the response object using either the halt method or by setting the is_halted flag directly on the response object. In these scenarios, the framework fails to properly interrupt the subsequent cleanup process. The cleanup routine proceeds to discard essential components of the current request context, including the request object, the response object, and any associated session data that the dispatcher has not yet fully consumed or processed. Because this discarding occurs before the normal flow can be safely terminated, the application state becomes corrupted or inconsistent. Consequently, despite the handler's explicit instruction to halt processing, the dispatcher continues its operation and proceeds to execute the refused route. This behavior contradicts the expected security model where a halted response should effectively terminate all further activity related to that specific request instance.
The operational impact of this vulnerability is significant for applications relying on Dancer2 for sensitive operations such as authentication checks or authorization validations performed within before hooks. If an attacker can trigger conditions that cause a hook to die, and subsequently manipulate the exception handler to halt execution, they may bypass these protective measures entirely. The refusal check implemented in certain hooks is not enforced against the route body itself; instead, only the caller receives the indication of refusal while the actual code within the route continues to execute. This means that writes or side effects defined inside the route body will still land and affect the application state or database even though the logical flow was intended to be stopped. For instance, if a before hook is designed to reject requests from unauthorized users by dying on failure, an attacker could potentially exploit this race condition in exception handling to ensure their request proceeds despite being rejected, leading to potential authorization bypasses.
From a technical perspective, this issue highlights deficiencies in the control flow unwinding mechanism within the Perl framework's core. The use of with_return for halting is intended to unwind the stack cleanly before cleanup runs, but in versions prior to 2.2.0, this logic was not sufficiently robust against all paths where exceptions occur. This aligns with CWE-841 Improper Enforcement of Behavioral Workflow and CWE-94 Improper Control of Generation of Code or Command if the route execution leads to arbitrary code execution depending on the specific payload used in the refused route. Furthermore, from an adversary perspective, this could facilitate ATT&CK technique T1068 Exploitation for Privilege Escalation if it allows access to restricted resources that should have been blocked by authentication hooks.
To mitigate this vulnerability, organizations running Dancer2 applications must upgrade immediately to version 2.2.0 or later where the logic governing hook exceptions and response halting has been corrected. Developers should also review their exception handling strategies to ensure they do not rely on implicit state preservation during cleanup phases that might be prematurely terminated. Implementing additional validation layers at multiple points in the request lifecycle can provide defense-in-depth against such logical flaws. It is crucial to test all authentication and authorization hooks thoroughly under conditions where exceptions are thrown, ensuring that halted responses truly prevent any subsequent route execution or data mutation. Until an upgrade is performed, applying workarounds such as avoiding the use of die statements within critical security hooks or manually managing session state persistence might offer limited protection, though upgrading remains the only definitive solution to address this structural defect in the framework's request handling architecture.