CVE-2021-3828: nltk
CVSS: 7.5v3.0HighModified
AliasesMGASA-2023-0302GHSA-2ww3-fxvq-293jPYSEC-2021-356UBUNTU-CVE-2021-3828USN-5215-1DEBIAN-CVE-2021-3828openSUSE-SU-2024:11958-1openSUSE-SU-2025:15099-1
Published 27-09-2021Last modified 03-08-2024
Vulnerability summary
CVE-2021-3828 is a high (CVSS 7.5) vulnerability in nltk. EPSS estimates a 1.59% chance of exploitation in the next 30 days, higher than 75.3% of scored vulnerabilities. 1 public exploit is recorded.
CVSS score
7.5/10
010
High · v3.0 (CVE.org)EPSS score
1.59%
0%100%
Low · -0.11 pp in 30 daysKEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits1reference
Advisory lineage
Upstream 0 · Downstream 1 · Related 1Timeline
- 27-09-2021PublishedVulnerability first disclosed.
- 03-08-2024Last modifiedVulnerability information updated.
Description
nltk is vulnerable to Inefficient Regular Expression Complexity
CVSS metrics
9 scores · 5 sources · 4 versionsHigh 8.7Preferred score · OSV · Pypi (Ecosystem advisory) · calculated from vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NSourcesSingle source
High 7.5Preferred score · OSV · Pypi (Ecosystem advisory) · calculated from vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HSourcesAll 4 agree
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
High 7.5Preferred score · CVE.org (CNA)
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HSourcesAll 3 agree
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- NVDNIST7.5HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Medium 5.0Preferred score · NVD (NIST)
AV:N/AC:L/Au:N/C:N/I:N/A:PSourcesSingle source
EPSS trend
Probability
1.59%
Chance of exploitation in the next 30 days
Percentile
75%
Versus all other CVEs
30-day change
-0.11 pp
From 1.70% on 19-09-2026
19-09-202619-10-2026
EPSS score1.59%
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
1 foundExploit Reference (huntr.dev)
Maturity: unknown
Weaknesses
CWE · root cause- CWE-1333Inefficient Regular Expression ComplexityThe product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.
- CWE-697Incorrect ComparisonThe product compares two entities in a security-relevant context, but the comparison is incorrect.
Affected systems
Mageia2 products
- python-nltk< 3.6.6-1.mga8
- python-regex< 2022.9.13-1.mga8
Debian1 product
- nltk< 3.6.5-1
Opensuse1 product
- python-nltk&distro=openSUSE Tumbleweed< 3.9.1-2.4 | < 3.7-1.1
PyPI1 product
- nltk< 277711ab1dec729e626b27aab6fa35ea5efbd7e6 | < 3.6.4
Ubuntu1 product
- nltk< 3.1-1ubuntu0.1+esm1 | < 3.2.5-1ubuntu0.1+esm1 | < 3.4.5-2ubuntu0.1~esm1 | < 3.6.5-1
6 vendors · 8 products
References
15 links- huntr.dev/bounties/d19aed43-75bc-4a03-91a0-4d0bb516bc32X Refsource CONFIRMWEBREPORTExploitPatchThird Party Advisory
- github.com/nltk/nltk/commit/277711ab1dec729e626b27aab6fa35ea5efbd7e6X Refsource MISCWEBFIXPatchThird Party Advisory
- github.com/nltk/nltkPACKAGE
Show all 15 references
- lists.opensuse.org/archives/…Advisory