What is CVE-2021-3828?

CVE-2021-3828 is a high-severity vulnerability in Nltk, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2021-09-27.

How severe is CVE-2021-3828?

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

Vulnerability in Nltk

CVE-2021-3828

nltk is vulnerable to Inefficient Regular Expression Complexity

Vulnerability class: ReDoS (Regular Expression Denial of Service)

Published 2021-09-27 · 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: 0.017 (76.3th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 76th percentile — 76.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.017 · newest: 0.017 · change: 0.000

Affected products

Nltk
Nltk Nltk/nltk — versions unspecified

Weakness classification (CWE)

References

huntr.dev/bounties/d19aed43-75bc-4a03-91a0-4d0bb516bc32 (Exploit, Patch, Third Party Advisory)
github.com/nltk/nltk/commit/277711ab1dec729e626b27aab6fa35ea5efbd7e6 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3828?: CVE-2021-3828 is a high-severity vulnerability in Nltk, classified under Inefficient Regular Expression Complexity. CVSS score: 7.5/10. Published 2021-09-27.
How severe is CVE-2021-3828?: High severity. CVSS v3 base score is 7.5 out of 10.