CVE-2026-31865 Elysia Cookie Value Prototype Pollution
Prototype pollution in Elysia cookie handling allows attackers to override properties, potentially leading to code execution or security bypasses.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31865?
CVE-2026-31865 is a medium-severity vulnerability in elysiajs elysia, published on 18 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Elysia is a Typescript framework for request validation, type inference, OpenAPI documentation, and client-server communication. Prior to version 1.4.27, an Elysia cookie can be overridden by prototype pollution , eg. `__proto__`. This issue is patched in 1.4.27. As a workaround, use t.Cookie validation to enforce validation value and/or prevent iterable over cookie if possible.
Weakness: CWE-1321
Which versions are affected by CVE-2026-31865?
2 open source packages ship an affected version, including elysia. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
elysia npm | All versions | 1.4.27 |
elysia npm | All versions | 1.4.27 |
Products include Elysiajs Elysia.
How do I fix CVE-2026-31865?
Upgrade elysia to 1.4.27 or later.
Is CVE-2026-31865 being exploited?
There is no known exploitation of CVE-2026-31865 in the wild and no public exploit code.
Other vulnerabilities in elysiajs elysia
Sources
Also known as GHSA-8hq9-phh3-p2wp.