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    CVE-2026-80206

    NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.

    Published:Aug 26, 2026
    Last Modified:Aug 26, 2026
    EPS:Aug 26, 2026
    EPSS Score:0.0025
    CVSS Score:5.9

    Affected Products

    Vendor
    Nltk
    Product
    Nltk

    Exploits

    https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-492 Regular Expression Exponential Blowup

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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