CVE-2021-3828

mediumpriority · track · 31EPSS 0.016 · 76 %ileEUUS

grimoire priorityP3 · Track

Exploitable?

—

no known exploitation

Likely / severe?

1.59% (76th) EPSS

CVSS 5 · medium

Is it mine?

3 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · osv · nvd

EPSS · scored 2026-10-27

nltk is vulnerable to Inefficient Regular Expression Complexity

cvss

Technical severity, 0–10. One row per scoring source.

7.5

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 5–7.5

v2.05mediumAV:N/AC:L/Au:N/C:N/I:N/A:Pprimary · NVD / NIST USexploitability 10 · impact 2.9

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 3.6

v3.07.5highCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · ENISA EU

v3.07.5highCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · security@huntr.devexploitability 3.9 · impact 3.6

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsecondary · OSV

v3.16.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-697USprimaryCWE-1333USCWE-1333USCWE-697US

affected products (3)

Products and version ranges known to be affected.

nltk nltk/nltk≤ unspecified ≤3.6.3enisa_euvdEU
nltk nltk≤ 3.6.3nvdUScpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:*
PyPI nltk< 3.6.4osvUSpkg:pypi/nltk

advisories (2)

Vendor and ecosystem advisories describing this.

GHSA-2ww3-fxvq-293jNLTK Vulnerable to REDoS2021-09-29ghsa · osvUS
The nltk package is vulnerable to ReDoS (regular expression denial of service). An attacker that is able to provide as an input to the [`_read_comparison_block()`(https://github.com/nltk/nltk/blob/23f4b1c4b4006b0cb3ec278e801029557cec4e82/nltk/corpus/reader/comparative_sents.py#L259) function in the file `nltk/corpus/reader/comparative_sents.py` may cause an application to consume an excessive amount of CPU.
PYSEC-2021-3562021-09-27vendor · osvUS
nltk is vulnerable to Inefficient Regular Expression Complexity

also known as (6)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd osv nvd NVD CVE.org MITRE

published 2021-09-27modified 2026-06-17

related (221)

Related entries.

ID	severity	EPSS	exploitable	published
CVE-2024-5217US	critical9.8OT critical	99.6% (100th)	KEV	2024-07-10
ServiceNow has addressed an input validation vulnerability that was identified in the Washington DC, Vancouver, and earlier Now Platform releases. This vulnerability could enable a…
CVE-2020-5849US	high7.5OT critical	93.2% (100th)	KEV	2020-03-16
Unraid 6.8.0 allows authentication bypass.
CVE-2020-8864US	high8.8	81.7% (100th)	—	2020-03-23
This vulnerability allows network-adjacent attackers to bypass authentication on affected installations of D-Link DIR-867, DIR-878, and DIR-882 routers with firmware 1.10B04. Authe…
CVE-2023-32571US	critical9.8	34.9% (98th)	Exploit	2023-06-22
Dynamic Linq 1.0.7.10 through 1.2.25 before 1.3.0 allows attackers to execute arbitrary code and commands when untrusted input to methods including Where, Select, OrderBy is parsed…
CVE-2019-10071US	critical9.8	8.75% (95th)	—	2019-09-16
The code which checks HMAC in form submissions used String.equals() for comparisons, which results in a timing side channel for the comparison of the HMAC signatures. This could le…

+216 more

references (7)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan