CVE-2026-56669: Elysia: Inefficient Algorithmic Complexity and Interpretation Conflict
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to 1.4.29, Elysia uses getAll in form data normalization for multipart/form-data endpoints, causing the amount of work to grow quadratically with the number of unique key-value pairs and allowing CPU exhaustion. This issue is fixed in version 1.4.29.
Other sources
Elysia v1.4.28 is vulnerable to denial-of-service attacks due to CPU exhaustion in the form data normalization code.
Elysia uses getAll to retrieve value from FormData. It is called directly relative to the total number of key-value pairs in the form data. The total amount of work the for loop has to do grows quadratically, so doubling the number of unique key-value pairs quadruples the amount of work. In the above PoC, each .getAll call scans through all of the n key-value pairs in the form data. Because there are n unique keys in the form data, there are .getAll calls, so in total the form data normalizer has to scan n x n key-value pairs.
Impact Endpoints using multipart/form-data
Patches 1.4.29
Workarounds no 100% confirm workaround beside updating the patch
— GitHub
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/elysiato a version that resolves this vulnerability.Fixed in 1.4.29 - Upgrade
Upgrade
Elysiato a version that resolves this vulnerability.Fixed in 1.4.29
Event History
Frequently Asked Questions
What is the severity of CVE-2026-56669?
CVE-2026-56669 has a high severity rating of 7.5.
What type of vulnerability is CVE-2026-56669?
CVE-2026-56669 is characterized by inefficient algorithmic complexity that can impact performance.
How do I fix CVE-2026-56669?
To fix CVE-2026-56669, update to Elysia version 1.4.29 or later.
What software is affected by CVE-2026-56669?
CVE-2026-56669 affects the Elysia framework, which is used for request validation and type inference in TypeScript.
What is the impact of CVE-2026-56669?
The impact of CVE-2026-56669 is that it can cause performance degradation under specific conditions due to inefficient handling of multipart/form-data.