Denial of Service in Elysia via Algorithmic Complexity

Elysia versions prior to 1.4.29 contain an algorithmic complexity vulnerability (CVE-2026-56669) within the framework's multipart/form-data normalization logic. When the framework processes incoming form data, the internal getAll method used to retrieve values operates with quadratic time complexity relative to the number of key-value pairs provided. Specifically, for each unique key in the form data, the normalization process scans all existing key-value pairs. Consequently, an attacker can craft a malicious multipart request containing a large number of unique keys, forcing the application to perform n-squared operations. This results in significant CPU consumption, potentially leading to a denial-of-service state for the affected application endpoint. The issue is resolved in version 1.4.29, which optimizes the data retrieval process to prevent the identified CPU exhaustion.

Impact

The vulnerability directly impacts web applications and API endpoints built using the Elysia framework that accept multipart/form-data uploads. Successful exploitation allows an unauthenticated attacker to cause excessive CPU utilization on the server, potentially rendering the service unresponsive to legitimate users.

Recommendation

Prioritized actions for development and security engineering teams:

• Upgrade the Elysia dependency to version 1.4.29 or later immediately to incorporate the algorithmic fix for CVE-2026-56669.
• Audit existing infrastructure to identify internet-facing endpoints processing multipart form data.
• Implement request size and complexity limits at the web application firewall (WAF) or load balancer level to mitigate potential resource exhaustion attacks while the patching process is completed.