CVE-2026-90535 in Flowise
Summary
by MITRE • 09/12/2026
Flowise versions before 3.1.4 contain an unauthenticated denial of service vulnerability in the /api/v1/text-to-speech/abort endpoint that accepts user-supplied chatflowId and chatId without ownership verification. Attackers can terminate active chatflow predictions for any user by submitting requests with known chatflow and chat identifiers, causing targeted service disruption.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/12/2026
The vulnerability identified in Flowise versions prior to 3.1.4 represents a critical failure in access control mechanisms within the application's text-to-speech processing module. Specifically, the /api/v1/text-to-speech/abort endpoint is designed to terminate ongoing speech synthesis operations for specific chat sessions. However, this endpoint lacks proper authentication and authorization checks regarding ownership of the targeted resources. The system accepts user-supplied parameters including chatflowId and chatId without verifying that the requesting entity has legitimate administrative or session-based rights over those identifiers. This architectural flaw allows any unauthenticated actor to interact with internal state management functions intended for authorized users only, fundamentally undermining the isolation between different tenant sessions within a multi-user environment.
From a technical perspective, the core issue lies in the absence of identity verification before executing destructive actions on shared resources. In typical secure implementations, an abort request must be validated against the current session token or user context to ensure that the caller is indeed the owner of the chatflow and chatId being targeted. By bypassing this check, the application treats all incoming requests as valid regardless of their origin. This allows attackers who can enumerate or guess valid chatflow and chat identifiers to send maliciously crafted HTTP POST requests to the abort endpoint. The server processes these requests immediately, triggering the termination logic for active predictions belonging to unsuspecting users.
The operational impact of this vulnerability is significant in environments where Flowise serves multiple concurrent users or handles sensitive conversational data. An attacker can cause a targeted denial of service by systematically terminating active text-to-speech operations. This disruption not only degrades user experience but also wastes computational resources as the system may attempt to recover from interrupted states or retry failed predictions. In high-throughput scenarios, such abuse could lead to resource exhaustion if an attacker floods the endpoint with abort requests for various valid identifiers. Furthermore, this behavior can be leveraged in conjunction with other vulnerabilities to escalate privileges or disrupt critical business workflows that rely on uninterrupted speech synthesis capabilities.
This vulnerability aligns closely with CWE-862 Missing Authorization and CWE-754 Improper Check for Unusual or Exceptional Conditions from the Common Weakness Enumeration standard, as it involves a failure to verify user permissions before performing an action. In terms of offensive security frameworks, this behavior corresponds to MITRE ATT&CK technique T1039 Known Application Software Denial of Service via API abuse, where attackers exploit legitimate functionality to disrupt service availability. The lack of rate limiting or input validation on the abort endpoint further exacerbates the risk by allowing rapid-fire requests that amplify the denial-of-service effect.
To mitigate this vulnerability, organizations running Flowise versions before 3.1.4 should upgrade immediately to version 3.1.4 or later where these access control checks have been implemented. For environments unable to patch immediately, network-level controls such as Web Application Firewalls can be configured to restrict access to the /api/v1/text-to-speech/abort endpoint based on IP reputation or known user agent patterns. Additionally implementing strict rate limiting and requiring valid session tokens for all API interactions involving state-changing operations will help prevent unauthorized termination of active processes. Regular security audits focusing on authorization logic in RESTful endpoints are recommended to identify similar flaws across the application surface area.