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CVE-2021-43854— Inefficient Regular Expression Complexity in nltk

Quick assessment

Affected
nltk nltk
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Natural Language Toolkit（NLTK）是一款使用Python语言编写的自然语言处理工具包。 Natural Language Toolkit（NLTK） 3.6.5之前版本存在资源管理错误漏洞，该漏洞源于软件对于正则表达式的处理缺少过滤和转义，软件容易受到正则表达式拒绝服务(regular expression denial of service, ReDoS)攻击。该漏洞存在于PunktSentenceTokenizer、sent tokenize和word tokenize中。该

CVSS 7.5 · High EPSS 2.60% · P85

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking
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I. Basic Information for CVE-2021-43854

Vulnerability Information
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Vulnerability Title
Inefficient Regular Expression Complexity in nltk
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
Natural Language Toolkit 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Natural Language Toolkit（NLTK）是一款使用Python语言编写的自然语言处理工具包。 Natural Language Toolkit（NLTK） 3.6.5之前版本存在资源管理错误漏洞，该漏洞源于软件对于正则表达式的处理缺少过滤和转义，软件容易受到正则表达式拒绝服务(regular expression denial of service, ReDoS)攻击。该漏洞存在于PunktSentenceTokenizer、sent tokenize和word tokenize中。该
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
nltk nltk < 3.6.5 -

II. Public POCs for CVE-2021-43854

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III. Intelligence Information for CVE-2021-43854

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Patches & Fixes for CVE-2021-43854 (2)

Vendor Advisories for CVE-2021-43854 (1)

Other References for CVE-2021-43854 (1)

IV. Related Vulnerabilities

Same product: nltk
Same vendor: nltk
Same weakness: CWE-400

V. Comments for CVE-2021-43854

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