CVE-2021-3828 Inefficient Regular Expression Complexity in nltk/nltk

High 7.5 Published 27 Sep 2021 Updated 3 Aug 2024

Attackers can cause denial of service in the nltk library by submitting inputs that trigger inefficient regular expression complexity.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2021-3828?

CVE-2021-3828 is a high-severity denial of service vulnerability in nltk/nltk, published on 27 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

nltk is vulnerable to Inefficient Regular Expression Complexity

Weakness: CWE-697, CWE-1333

Which versions are affected by CVE-2021-3828?

3 open source packages ship an affected version, including nltk. It affects 1 product.

Package	Affected	Fixed in
`nltk` PyPI	All versions	`3.6.4`
`nltk` PyPI	All versions	`3.6.4`
`nltk` PyPI	All versions	`3.6.4`

Linux distribution packages (2)

`python-nltk` openSUSE:Tumbleweed	All versions	`3.7-1.1`
`python-nltk` openSUSE:Tumbleweed	All versions	`3.9.1-2.4`

Products include Nltk Nltk.

How do I fix CVE-2021-3828?

Upgrade nltk to 3.6.4 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2021-3828 being exploited?

There is no known exploitation of CVE-2021-3828 in the wild and no public exploit code.

Sources

Also known as DEBIAN-CVE-2021-3828, GHSA-2ww3-fxvq-293j, MGASA-2023-0302, PYSEC-2021-356, UBUNTU-CVE-2021-3828, USN-5215-1 and 2 more.