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    CVE-2021-43854

    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:Dec 23, 2021
    Last Modified:Nov 21, 2024
    EPS:Dec 23, 2021
    EPSS Score:0.00836
    CVSS Score:7.5

    Affected Products

    Vendor
    Nltk
    Product
    Nltk

    Exploits

    https://github.com/nltk/nltk/issues/2866https://github.com/nltk/nltk/pull/2869https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9xhttps://github.com/nltk/nltk/issues/2866https://github.com/nltk/nltk/pull/2869https://github.com/nltk/nltk/security/advisories/GHSA-f8m6-h2c7-8h9x

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    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High