How severe is CVE-2021-3842?

CVE-2021-3842 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-3842 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-3842?

CVE-2021-3842 primarily affects Nltk. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-3842?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-3842 published?

CVE-2021-3842 was published on 2022-01-04 and last updated on 2026-06-17.

CVE-2021-3842

CVE-2021-3842 is a high-severity vulnerability in Nltk with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1333.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (70th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-1333
Affected product: Nltk
Published: 2022-01-04
Last modified: 2026-06-17

Description

nltk is vulnerable to Inefficient Regular Expression Complexity

Frequently asked questions

What is CVE-2021-3842?: nltk is vulnerable to Inefficient Regular Expression Complexity
How severe is CVE-2021-3842?: CVE-2021-3842 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-3842 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (70th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-3842?: CVE-2021-3842 primarily affects Nltk. In total, 5 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-3842?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-3842 published?: CVE-2021-3842 was published on 2022-01-04 and last updated on 2026-06-17.

References

Affected products (5)

cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*

More vulnerabilities in Nltk

CVE-2026-0848 — Critical (CVSS 10.0): NLTK versions <=3.9.2 are vulnerable to arbitrary code execution due to improper input validation in the…
CVE-2025-14009 — High (CVSS 8.8): A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The _unzip_iter…
CVE-2026-33236 — High (CVSS 8.1): NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research…
CVE-2026-12252 — High (CVSS 7.8): In nltk/nltk versions 3.9.3 and earlier, five Stanford interface classes (StanfordPOSTagger, StanfordNERTagger,…
CVE-2026-12243 — High (CVSS 7.5): NLTK version 3.9.4 is vulnerable to a path traversal attack due to an incomplete fix for GitHub Issue #3504. The…
CVE-2026-54293 — High (CVSS 7.5): NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research…

All CVEs affecting Nltk →

Other CWE-1333 vulnerabilities

CVE-2026-35458 — Critical (CVSS 9.8): Gotenberg is an API for converting document formats. In 8.29.1 and earlier, Gotenberg uses dlclark/regexp2 to compile…
CVE-2023-29486 — Critical (CVSS 9.8): An issue was discovered in Heimdal Thor agent versions 3.4.2 and before 3.7.0 on Windows, allows attackers to bypass…
CVE-2026-25547 — Critical (CVSS 9.2): @isaacs/brace-expansion is a hybrid CJS/ESM TypeScript fork of brace-expansion. Prior to version 5.0.1,…
CVE-2023-29487 — Critical (CVSS 9.1): An issue was discovered in Heimdal Thor agent versions 3.4.2 and before on Windows and 2.6.9 and before on macOS,…
CVE-2026-47138 — High (CVSS 8.7): Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Prior to…
CVE-2025-6998 — High (CVSS 8.7): ReDoS in strip_whitespaces() function in cps/string_helper.py in Calibre Web and Autocaliweb allows unauthenticated…

Browse all CWE-1333 vulnerabilities →