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Vulnerability Details 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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.003
EPSS Ranking 16.2%
CVSS Severity
CVSS v3 Score 5.9
Products affected by CVE-2026-80206
  • Nltk » Nltk » Version: 2.0.1
    cpe:2.3:a:nltk:nltk:2.0.1
  • Nltk » Nltk » Version: 2.0.3
    cpe:2.3:a:nltk:nltk:2.0.3
  • Nltk » Nltk » Version: 2.0.4
    cpe:2.3:a:nltk:nltk:2.0.4
  • Nltk » Nltk » Version: 3.0.0
    cpe:2.3:a:nltk:nltk:3.0.0
  • Nltk » Nltk » Version: 3.0.1
    cpe:2.3:a:nltk:nltk:3.0.1
  • Nltk » Nltk » Version: 3.0.2
    cpe:2.3:a:nltk:nltk:3.0.2
  • Nltk » Nltk » Version: 3.0.3
    cpe:2.3:a:nltk:nltk:3.0.3
  • Nltk » Nltk » Version: 3.0.4
    cpe:2.3:a:nltk:nltk:3.0.4
  • Nltk » Nltk » Version: 3.0.5
    cpe:2.3:a:nltk:nltk:3.0.5
  • Nltk » Nltk » Version: 3.1
    cpe:2.3:a:nltk:nltk:3.1
  • Nltk » Nltk » Version: 3.10.0
    cpe:2.3:a:nltk:nltk:3.10.0
  • Nltk » Nltk » Version: 3.10.1
    cpe:2.3:a:nltk:nltk:3.10.1
  • Nltk » Nltk » Version: 3.10.2
    cpe:2.3:a:nltk:nltk:3.10.2
  • Nltk » Nltk » Version: 3.2
    cpe:2.3:a:nltk:nltk:3.2
  • Nltk » Nltk » Version: 3.2.1
    cpe:2.3:a:nltk:nltk:3.2.1
  • Nltk » Nltk » Version: 3.2.2
    cpe:2.3:a:nltk:nltk:3.2.2
  • Nltk » Nltk » Version: 3.2.3
    cpe:2.3:a:nltk:nltk:3.2.3
  • Nltk » Nltk » Version: 3.2.4
    cpe:2.3:a:nltk:nltk:3.2.4
  • Nltk » Nltk » Version: 3.2.5
    cpe:2.3:a:nltk:nltk:3.2.5
  • Nltk » Nltk » Version: 3.3
    cpe:2.3:a:nltk:nltk:3.3
  • Nltk » Nltk » Version: 3.4
    cpe:2.3:a:nltk:nltk:3.4
  • Nltk » Nltk » Version: 3.4.1
    cpe:2.3:a:nltk:nltk:3.4.1
  • Nltk » Nltk » Version: 3.4.3
    cpe:2.3:a:nltk:nltk:3.4.3
  • Nltk » Nltk » Version: 3.4.4
    cpe:2.3:a:nltk:nltk:3.4.4
  • Nltk » Nltk » Version: 3.4.5
    cpe:2.3:a:nltk:nltk:3.4.5
  • Nltk » Nltk » Version: 3.5
    cpe:2.3:a:nltk:nltk:3.5
  • Nltk » Nltk » Version: 3.6
    cpe:2.3:a:nltk:nltk:3.6
  • Nltk » Nltk » Version: 3.6.1
    cpe:2.3:a:nltk:nltk:3.6.1
  • Nltk » Nltk » Version: 3.6.2
    cpe:2.3:a:nltk:nltk:3.6.2
  • Nltk » Nltk » Version: 3.6.3
    cpe:2.3:a:nltk:nltk:3.6.3
  • Nltk » Nltk » Version: 3.6.4
    cpe:2.3:a:nltk:nltk:3.6.4
  • Nltk » Nltk » Version: 3.6.5
    cpe:2.3:a:nltk:nltk:3.6.5
  • Nltk » Nltk » Version: 3.6.6
    cpe:2.3:a:nltk:nltk:3.6.6
  • Nltk » Nltk » Version: 3.6.7
    cpe:2.3:a:nltk:nltk:3.6.7
  • Nltk » Nltk » Version: 3.7
    cpe:2.3:a:nltk:nltk:3.7
  • Nltk » Nltk » Version: 3.8
    cpe:2.3:a:nltk:nltk:3.8
  • Nltk » Nltk » Version: 3.8.1
    cpe:2.3:a:nltk:nltk:3.8.1
  • Nltk » Nltk » Version: 3.9
    cpe:2.3:a:nltk:nltk:3.9
  • Nltk » Nltk » Version: 3.9.1
    cpe:2.3:a:nltk:nltk:3.9.1
  • Nltk » Nltk » Version: 3.9.2
    cpe:2.3:a:nltk:nltk:3.9.2
  • Nltk » Nltk » Version: 3.9.3
    cpe:2.3:a:nltk:nltk:3.9.3
  • Nltk » Nltk » Version: 3.9.4
    cpe:2.3:a:nltk:nltk:3.9.4


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