Prototype Pollution in Mikro-Orm
CVE-2026-34221
MikroORM is a TypeScript ORM for Node.js based on Data Mapper, Unit of Work and Identity Map patterns. Prior to versions 6.6.10 and 7.0.6, a prototype pollution vulnerability exists in the Utils.merge helper used internally by MikroORM when merging object structures. The function did not prevent special keys such as __proto__, constructor, or prototype, allowing attacker-controlled input to modify the JavaScript object prototype when merged. This issue has been patched in versions 6.6.10 and 7.0.6.
Vulnerability class: Prototype Pollution
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H.
EPSS exploit prediction
EPSS: 0.005 (41.4th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 41.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.005 · change: +0.001
Affected products
- Mikro-Orm — versions < 6.6.10, >= 7.0.0-rc.0, < 7.0.6
- Mikro-Orm Mikroorm
Weakness classification (CWE)
References
- github.com/mikro-orm/mikro-orm/security/advisories/GHSA-qpfv-44f3-qqx6 (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-34221?
- CVE-2026-34221 is a critical-severity vulnerability in Mikro-Orm, classified under Improperly Controlled Modification of Object Prototype Attributes (Prototype Pollution). CVSS score: 9.1/10. Published 2026-03-31.
- How severe is CVE-2026-34221?
- Critical severity. CVSS v3 base score is 9.1 out of 10.