# CVE-2026-34221: MikroORM has Prototype Pollution in Utils.merge

> Attacker-controlled input can pollute JavaScript prototypes via MikroORM's merge utility, potentially leading to code execution or privilege escalation.

- **Severity:** High 8.3 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:H/SC:N/SI:L/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 31 Mar 2026
- **Updated:** 31 Mar 2026
- **Also known as:** GHSA-qpfv-44f3-qqx6

## What is CVE-2026-34221?

CVE-2026-34221 is a high-severity unsafe deserialization vulnerability in mikro-orm, published on 31 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-34221?

4 open source packages ship an affected version, including @mikro-orm/core. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@mikro-orm/core` | npm | All versions | 6.6.10 |
| `@mikro-orm/core` | npm | All versions | 6.6.10 |
| `@mikro-orm/core` | npm | From 7.0.0-dev.0 | 7.0.6 |
| `@mikro-orm/core` | npm | From 7.0.0-dev.0 | 7.0.6 |

Products: Mikro-Orm Mikroorm.

## How do I fix CVE-2026-34221?

Upgrade @mikro-orm/core to a fixed version for your release line: 6.6.10 or 7.0.6.

## Is CVE-2026-34221 being exploited?

There is no known exploitation of CVE-2026-34221 in the wild and no public exploit code.

## Other vulnerabilities in mikro-orm

- [CVE-2026-34220](https://insights.sbomify.com/CVE-2026-34220/): MikroORM is vulnerable to SQL Injection via specially crafted object (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34221 and fix it if it is affected.

What it is: CVE-2026-34221 is a high-severity unsafe deserialization vulnerability in mikro-orm, published on 31 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-34221 in the wild and no public exploit code.

Affected packages and fixed versions:
- @mikro-orm/core (npm): affected all versions; fixed in 6.6.10
- @mikro-orm/core (npm): affected all versions; fixed in 6.6.10
- @mikro-orm/core (npm): affected from 7.0.0-dev.0; fixed in 7.0.6
- @mikro-orm/core (npm): affected from 7.0.0-dev.0; fixed in 7.0.6

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-34221/ (Markdown: https://insights.sbomify.com/CVE-2026-34221/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34221
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34221
- OSV: https://osv.dev/vulnerability/CVE-2026-34221

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34221/
Summaries are generated and may contain mistakes; the official description above is the record.