CVE-2021-3842: Inefficient Regular Expression Complexity in nltk/nltk
First published: Tue Jan 04 2022(Updated: )
Last updated 24 March 2025
Credit: security@huntr.dev security@huntr.dev
| Affected Software | Affected Version | How to fix |
|---|---|---|
| pip/nltk | <3.6.6 | 3.6.6 |
| debian/nltk | <=3.5-1 | 3.8-1 3.9.1-2 |
| Natural Language Toolkit | <3.6.6 | |
| Debian Linux | =9.0 | |
| Debian Linux | =10.0 | |
| Debian Linux | =11.0 | |
| Red Hat Fedora | =35 |
Never miss a vulnerability like this again
Sign up to SecAlerts for real-time vulnerability data matched to your software, aggregated from hundreds of sources.
Reference Links
- https://huntr.dev/bounties/761a761e-2be2-430a-8d92-6f74ffe9866a
- https://github.com/nltk/nltk/commit/2a50a3edc9d35f57ae42a921c621edc160877f4d
- https://nvd.nist.gov/vuln/detail/CVE-2021-3842
- https://github.com/nltk/nltk/pull/2906
- https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2022-5.yaml
- https://github.com/advisories/GHSA-rqjh-jp2r-59cj (Advisory)
- https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-3842
- https://launchpad.net/bugs/cve/CVE-2021-3842
- https://security-tracker.debian.org/tracker/CVE-2021-3842
- https://ubuntu.com/security/CVE-2021-3842
- https://huntr.dev/bounties/761a761e-2be2-430a-8d92-6f74ffe9866a/
Frequently Asked Questions
What is CVE-2021-3842?
CVE-2021-3842 is a vulnerability in NLTK that allows for Regular Expression Denial of Service (REDoS) attacks in certain RegexpTaggers used in the functions `get_pos_tagger` and `malt_regex_tagger`.
How severe is CVE-2021-3842?
CVE-2021-3842 has a severity score of 7.5, which is considered high.
What software is affected by CVE-2021-3842?
NLTK version 3.6.6 installed through pip is affected by CVE-2021-3842.
How can I fix CVE-2021-3842?
To fix CVE-2021-3842, update NLTK to version 3.6.6 using pip.
Where can I find more information about CVE-2021-3842?
You can find more information about CVE-2021-3842 at the following references: [NVD](https://nvd.nist.gov/vuln/detail/CVE-2021-3842), [NLTK GitHub Commit](https://github.com/nltk/nltk/commit/2a50a3edc9d35f57ae42a921c621edc160877f4d), [Huntr Bounty](https://huntr.dev/bounties/761a761e-2be2-430a-8d92-6f74ffe9866a).
- agent/type
- agent/remedy
- collector/mitre-cve
- source/MITRE
- agent/severity
- agent/weakness
- agent/title
- agent/first-publish-date
- collector/github-advisory-latest
- source/GitHub
- alias/GHSA-rqjh-jp2r-59cj
- alias/CVE-2021-3842
- agent/software-canonical-lookup
- agent/author
- collector/github-advisory
- agent/trending
- collector/usn-cve
- source/Ubuntu
- agent/references
- collector/security-tracker-debian
- source/Debian
- agent/last-modified-date
- agent/description
- collector/launchpad-cve
- source/Launchpad
- agent/source
- agent/event
- collector/nvd-cve
- source/NVD
- agent/software-canonical-lookup-request
- agent/tags
- agent/softwarecombine
- collector/nvd-index
- package-manager/pip
- package-manager/debian
- vendor/nltk
- canonical/natural language toolkit
- vendor/debian
- canonical/debian linux
- version/debian linux/9.0
- version/debian linux/10.0
- version/debian linux/11.0
- vendor/fedoraproject
- canonical/red hat fedora
- version/red hat fedora/35