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    CVE-2026-81722

    nltk PorterStemmer in versions <= 3.10.2 (fixed in 3.10.3) contains an inefficient-algorithmic-complexity denial of service in PorterStemmer.stem(). The _is_consonant() helper walks backward over the entire run of trailing 'y' characters on every call, and _measure() invokes it for each stem position, causing O(n^2) behavior. A single ~20-50 KB untrusted token consisting of a long run of the letter 'y' followed by a matching suffix (e.g., 'ness') can pin a CPU core for seconds to minutes, causing availability impact.

    Published:Aug 27, 2026
    Last Modified:Aug 31, 2026
    EPS:Aug 27, 2026
    EPSS Score:0.00363
    CVSS Score:7.5

    Affected Products

    Vendor
    Nltk
    Product
    Nltk

    Exploits

    https://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94ghttps://github.com/nltk/nltk/security/advisories/GHSA-ww6m-cw3f-q94g

    Common Attack Pattern Enumeration and Classification (CAPEC)

    No CAPEC recorded yet

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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