What’s Vulnerable › Vulnerabilities

CVE-2021-3842: Inefficient Regular Expression Complexity in nltk/nltk

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.5% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2022-01-04 · updated 2026-06-17
• Weakness: CWE-1333

Description

nltk is vulnerable to Inefficient Regular Expression Complexity

Affected products

• Debian Linux: 9.0, 10.0, 11.0
• Fedoraproject Fedora: 35
• nltk: before 3.6.6 — fixed in 3.6.6

How to fix

Upgrade to a fixed version: nltk 3.6.6. Check the vendor advisory for mitigations.

References

• https://github.com/nltk/nltk/commit/2a50a3edc9d35f57ae42a921c621edc160877f4d
• https://huntr.dev/bounties/761a761e-2be2-430a-8d92-6f74ffe9866a
• https://github.com/nltk/nltk/commit/2a50a3edc9d35f57ae42a921c621edc160877f4d
• https://huntr.dev/bounties/761a761e-2be2-430a-8d92-6f74ffe9866a

Get alerted when CVE-2021-3842 or the next vulnerability affects your stack