Quick answers
- Is CVE-2026-31865 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-31865 being exploited in the wild.
- How severe is CVE-2026-31865?
- Low severity, with a CVSS score of 3.1, published 17 March 2026.
- Which products and versions are affected?
- elysia (npm) SEMVER:introduced=0,fixed=1.4.27.
- Is there a fix for CVE-2026-31865?
- Yes. elysia (npm): upgrade to 1.4.27 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-31865 attacked?
- It is attacked over the network.
- Am I affected by CVE-2026-31865?
- Check whether you run elysia (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- elysia (npm): upgrade to 1.4.27 or later
npm install elysia@1.4.27
Technical details
The vulnerability is a prototype pollution flaw (CWE-1321) in Elysia's cookie parsing mechanism. By sending a specially crafted cookie with the name "__proto__" followed by a JSON payload, an attacker can pollute the prototype chain and override cookie values. The vulnerability affects all versions before 1.4.27 and requires only network access with no authentication or user interaction. An attacker can exploit this to read sensitive cookie data and modify cookie properties, potentially compromising session management and application logic. The vulnerability is patched in version 1.4.27.
Affected products
- Elysia Elysia < 1.4.27
Identifiers
- CVE-2026-31865
- GHSA-8hq9-phh3-p2wp
Timeline
- 2026-03-17: disclosed
- 2026-03-17: patched: version 1.4.27