CVE-2026-59299 in Spring Cloud Function
Summary
by MITRE • 08/27/2026
Composition lookup can potentially poison base function in Spring Cloud Function. Spring Cloud Function 5.0.0 - 5.0.3 Spring Cloud Function 4.3.0 - 4.3.4 Spring Cloud Function 4.2.0 - 4.2.7 Spring Cloud Function 3.2.16 and earlier
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Analysis
by VulDB Data Team • 08/27/2026
Spring Cloud Function is a framework that enables developers to build serverless applications using standard Java interfaces, allowing functions to be deployed across various cloud providers such as AWS Lambda, Azure Functions, or Google Cloud Functions. The vulnerability identified in versions ranging from 3.2.16 and earlier through 5.0.3 involves a critical flaw within the composition lookup mechanism used by the framework. This component is responsible for resolving function definitions when multiple functions are composed together to create complex workflows. In this specific implementation, the logic governing how these compositions reference base functions contains a design weakness that allows an attacker to manipulate the resolution process through crafted input data.
The core technical flaw lies in the insufficient validation of composition references during runtime lookup operations. When Spring Cloud Function processes a request involving composed functions, it attempts to resolve the underlying function definitions based on identifiers provided by the client or configuration. Due to inadequate sanitization and boundary checks within this lookup logic, an attacker can supply specially crafted input that alters the intended resolution path. This manipulation effectively poisons the base function reference, causing the application to execute a different function than originally intended or to access internal components that should remain isolated from external invocation. This behavior constitutes a form of insecure direct object reference where the system fails to properly verify that the requested resource corresponds to the expected secure target.
From an operational perspective, this vulnerability poses significant risks to the integrity and availability of serverless applications built on Spring Cloud Function. By poisoning the base function lookup, attackers can potentially trigger unintended code execution paths within the application environment. This could lead to unauthorized access to sensitive data stored or processed by the compromised functions, as well as potential denial-of-service conditions if the poisoned reference causes infinite loops or resource exhaustion during resolution attempts. Furthermore, because Spring Cloud Function often serves as a gateway for external requests in serverless architectures, this flaw expands the attack surface significantly, allowing remote attackers who can interact with the function endpoints to influence internal application logic without needing direct access to the underlying infrastructure codebase.
This vulnerability aligns closely with CWE-20 Improper Input Validation and CWE-918 Server-Side Request Forgery (SSRF) variants where the server makes requests based on user-supplied data that are not properly validated against a whitelist of allowed targets. In terms of the MITRE ATT&CK framework, this behavior maps to T1564.002 Hidden Files and Directories or more accurately to T1190 Exploit Public-Facing Application, as it involves exploiting a vulnerability in an internet-facing service to achieve unauthorized control over application flow. The ability to redirect function execution represents a critical breach of the principle of least privilege within the serverless context, where functions are typically expected to operate with minimal permissions and isolated scopes.
Mitigation strategies for this issue require immediate upgrading to patched versions of Spring Cloud Function that address the composition lookup logic. For organizations unable to upgrade immediately due to compatibility constraints, implementing strict input validation at the API gateway level is essential. This includes whitelisting allowed function names and rejecting any requests containing characters or patterns indicative of path traversal or injection attempts related to function identifiers. Additionally, deploying Web Application Firewalls with rules specifically tuned for Spring Framework vulnerabilities can provide a layer of defense by blocking malicious payloads before they reach the application logic. Regular security audits focusing on how external inputs influence internal routing decisions are also recommended to identify similar weaknesses in other components of the serverless architecture.