What is CVE-2021-3842?

CVE-2021-3842 is a high-severity vulnerability in Nltk, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2022-01-04.

How severe is CVE-2021-3842?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Nltk

CVE-2021-3842

nltk is vulnerable to Inefficient Regular Expression Complexity

Vulnerability class: ReDoS (Regular Expression Denial of Service)

Published 2022-01-04 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.015 (72.6th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 73rd percentile — 72.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.015 · newest: 0.015 · change: 0.000

Affected products

Nltk
Nltk Nltk/nltk — versions unspecified
Debian Linux — versions 9.0, 10.0, 11.0
Fedoraproject Fedora — versions 35

Weakness classification (CWE)

CWE-1333 — Inefficient Regular Expression Complexity

References

huntr.dev/bounties/761a761e-2be2-430a-8d92-6f74ffe9866a (Exploit, Patch, Third Party Advisory, Issue Tracking)
github.com/nltk/nltk/commit/2a50a3edc9d35f57ae42a921c621edc160877f4d (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3842?: CVE-2021-3842 is a high-severity vulnerability in Nltk, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2022-01-04.
How severe is CVE-2021-3842?: High severity. CVSS v3 base score is 7.5 out of 10.