NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Versions prior to 3.6.5 are vulnerable to regular expression denial of service (ReDoS) attacks. The vulnerability is present in PunktSentenceTokenizer, sent_tokenize and word_tokenize. Any users of this class, or these two functions, are vulnerable to the ReDoS attack. In short, a specifically crafted long input to any of these vulnerable functions will cause them to take a significant amount of execution time. If your program relies on any of the vulnerable functions for tokenizing unpredictable user input, then we would strongly recommend upgrading to a version of NLTK without the vulnerability. For users unable to upgrade the execution time can be bounded by limiting the maximum length of an input to any of the vulnerable functions. Our recommendation is to implement such a limit.
Published 2021-12-23 18:15:07
Updated 2022-01-04 16:38:21
Source GitHub, Inc.
View at NVD,   CVE.org
Vulnerability category: Denial of service

Exploit prediction scoring system (EPSS) score for CVE-2021-43854

0.27%
Probability of exploitation activity in the next 30 days EPSS Score History
~ 66 %
Percentile, the proportion of vulnerabilities that are scored at or less

CVSS scores for CVE-2021-43854

Base Score Base Severity CVSS Vector Exploitability Score Impact Score Score Source First Seen
5.0
MEDIUM AV:N/AC:L/Au:N/C:N/I:N/A:P
10.0
2.9
NIST
7.5
HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
3.9
3.6
GitHub, Inc.

CWE ids for CVE-2021-43854

  • The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources.
    Assigned by: security-advisories@github.com (Primary)

References for CVE-2021-43854

Products affected by CVE-2021-43854

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