CVE-2026-59321 in Spring Integration
Summary
by MITRE • 08/27/2026
A single ScriptEngine instance is reused for every message on a script-backed channel. For JSR-223 engines that report THREADING=null (not thread-safe, e.g. the Kotlin kts engine), concurrent message processing can corrupt engine-internal state, potentially leaking one message's payload/headers bindings into another message's script evaluation or throwing spurious exceptions. Spring Integration 7.1.0 Spring Integration 7.0.0 - 7.0.5 Spring Integration 6.5.0 - 6.5.10 Spring Integration 6.4.0 - 6.4.12 Spring Integration 5.5.21 and earlier
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Analysis
by VulDB Data Team • 08/28/2026
The vulnerability described involves a critical concurrency flaw within the script execution engine management of Spring Integration, specifically affecting versions ranging from 5.5.21 through 7.1.0 across multiple minor release branches including 6.4.x, 6.5.x, and 7.0.x. The core issue stems from the architectural decision to reuse a single ScriptEngine instance for processing every message on a script-backed channel rather than instantiating new engine instances per request or employing thread-local storage mechanisms. This design choice assumes that all JSR-223 compliant scripting engines are either stateless or inherently thread-safe, which is not universally true across the Java ecosystem. When an application processes messages concurrently over such channels, multiple threads may simultaneously invoke methods on the same ScriptEngine object, leading to race conditions and data corruption within the engine's internal state management structures.
This lack of synchronization becomes particularly severe when interacting with scripting engines that explicitly report THREADING as null in their properties map, indicating they are not thread-safe. A prominent example cited is the Kotlin kts engine, which falls into this category. In these scenarios, concurrent access results in unpredictable behavior where internal variables, bindings, and execution contexts can become interleaved between different message processing threads. This leads to a scenario known as state leakage, where data intended for one message's script evaluation context inadvertently leaks into another message's context. For instance, headers or payload bindings set by Thread A might be read or modified by Thread B during its own script execution cycle, causing logical errors that are difficult to reproduce and diagnose due to their non-deterministic nature depending on thread scheduling timing.
The operational impact of this vulnerability is significant for any production system relying on Spring Integration for message-driven architectures with concurrent processing capabilities. The primary consequence is the corruption of application logic driven by script evaluation results, which can lead to incorrect business decisions based on tainted data. Furthermore, the race conditions often manifest as spurious exceptions such as NullPointerExceptions or ClassCastException during runtime, causing service disruptions and potential denial-of-service conditions if not handled gracefully by upstream error handlers. In security-sensitive contexts, this state leakage could potentially expose sensitive information contained within message headers or payloads to unintended processing threads, violating confidentiality requirements even if no direct external exploitation vector exists for remote code execution in the traditional sense.
From a classification perspective, this vulnerability aligns with CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization, as it involves multiple concurrent accesses to a shared resource without adequate locking or isolation mechanisms. It also relates closely to CWE-481: Assigning Wrong Method Verb in Object-Oriented Programming if the underlying engine implementation fails to enforce thread safety contracts properly, though the root cause here is architectural misuse of non-thread-safe components. In terms of MITRE ATT&CK mapping, this does not represent a direct attack technique but rather a weakness that could be leveraged indirectly; however, it falls under Tactic TA0004: Privilege Escalation if state leakage allows bypassing logical access controls, or more accurately under the broader category of software faults that lead to availability and integrity compromises.
To mitigate this vulnerability, organizations must upgrade Spring Integration to a version where the script engine handling has been refactored to ensure thread safety. This typically involves either using thread-local ScriptEngine instances for each processing thread or switching to scripting engines that are explicitly documented as thread-safe with THREADING set to MULTI_THREAD_SINGLETON or similar safe values. If upgrading is not immediately feasible, developers should implement custom message channel configurations that enforce sequential execution of script evaluations on affected channels, thereby eliminating concurrency at the application level until a patch can be applied. Additionally, auditing all JSR-223 engine usages in the codebase to verify THREADING properties and replacing non-thread-safe engines with safer alternatives like GraalVM JavaScript or Nashorn (where applicable) provides long-term resilience against similar concurrency flaws.