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CVE-2026-81724

CVE-2026-81724 · NLTK before 3.10.3 Denial of Service via Uncontrolled Recursion

This page contains facts from public vulnerability sources. Check the original advisory before updating.

NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed Python's recursion limit and raise an unhandled RecursionError, crashing applications that parse user-supplied feature structures or feature grammars.

CVSS 6.9 · Medium · EPSS 0.5% · Fix available

Published
Updated

Stack: system · python

Affected products and versions

  • nltk

    Versions
    • ≥ 0, < 3.10.3: Affected (semver)
    • 3.10.3: Not affected (semver)

    Update to 3.10.3

  • nltk Debian:12

    Versions
    • 3.10.0-1
    • 3.10.1-1
    • 3.10.3-1
    • 3.8-1
    • 3.8.1-1
    • 3.9.1-1
    • 3.9.1-2
    • 3.9.2-1
    • 3.9.3-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Debian:13

    Versions
    • 3.10.0-1
    • 3.10.1-1
    • 3.10.3-1
    • 3.9.1-2
    • 3.9.2-1
    • 3.9.3-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Debian:14

    Versions
    • 3.10.0-1
    • 3.10.1-1
    • 3.9.1-2
    • 3.9.2-1
    • 3.9.3-1
    Affected ranges
    • ECOSYSTEM: < 3.10.3-1

    Update to 3.10.3-1

  • nltk PyPI

    Versions
    • 0.8
    • 0.9
    • 0.9.3
    • 0.9.4
    • 0.9.5
    • 0.9.6
    • 0.9.7
    • 0.9.8
    • 0.9.9
    • 2.0.1
    • 2.0.1rc1
    • 2.0.1rc2-git
    • 2.0.1rc3
    • 2.0.1rc4
    • 2.0.2
    • 2.0.3
    • 2.0.4
    • 2.0.5
    • 2.0b4
    • 2.0b5
    • 2.0b6
    • 2.0b7
    • 2.0b8
    • 2.0b9
    • 3.0.0
    • 3.0.0b1
    • 3.0.0b2
    • 3.0.1
    • 3.0.2
    • 3.0.3
    • 3.0.4
    • 3.0.5
    • 3.1
    • 3.10.0
    • 3.10.1
    • 3.10.2
    • 3.2
    • 3.2.1
    • 3.2.2
    • 3.2.3
    • 3.2.4
    • 3.2.5
    • 3.3
    • 3.4
    • 3.4.1
    • 3.4.2
    • 3.4.3
    • 3.4.4
    • 3.4.5
    • 3.5
    • 3.5b1
    • 3.6
    • 3.6.1
    • 3.6.2
    • 3.6.3
    • 3.6.4
    • 3.6.5
    • 3.6.6
    • 3.6.7
    • 3.7
    • 3.8
    • 3.8.1
    • 3.9
    • 3.9.1
    • 3.9.2
    • 3.9.3
    • 3.9.4
    • 3.9b1
    Affected ranges
    • ECOSYSTEM: < 3.10.3

    Update to 3.10.3

  • nltk Ubuntu:Pro:14.04:LTS

    Versions
    • 2.0~b9-0ubuntu4
    • 2.0~b9-0ubuntu4.1~esm2
    • 2.0~b9-0ubuntu4.1~esm4
    • 2.0~b9-0ubuntu4.1~esm5
    • 2.0~b9-0ubuntu4.1~esm6
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Ubuntu:Pro:16.04:LTS

    Versions
    • 3.0.4-1
    • 3.0.5-1
    • 3.1-1
    • 3.1-1ubuntu0.1
    • 3.1-1ubuntu0.1+esm1
    • 3.1-1ubuntu0.1+esm2
    • 3.1-1ubuntu0.1+esm3
    • 3.1-1ubuntu0.1+esm4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Ubuntu:Pro:18.04:LTS

    Versions
    • 3.2.4-1
    • 3.2.5-1
    • 3.2.5-1ubuntu0.1
    • 3.2.5-1ubuntu0.1+esm1
    • 3.2.5-1ubuntu0.1+esm2
    • 3.2.5-1ubuntu0.1+esm3
    • 3.2.5-1ubuntu0.1+esm4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Ubuntu:Pro:20.04:LTS

    Versions
    • 3.4.5-1
    • 3.4.5-2
    • 3.4.5-2ubuntu0.1~esm1
    • 3.4.5-2ubuntu0.1~esm2
    • 3.4.5-2ubuntu0.1~esm3
    • 3.4.5-2ubuntu0.1~esm4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Ubuntu:Pro:22.04:LTS

    Versions
    • 3.5-1
    • 3.6.5-1
    • 3.6.7-1
    • 3.7-1
    • 3.7-1ubuntu0.1~esm1
    • 3.7-1ubuntu0.1~esm2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Ubuntu:Pro:24.04:LTS

    Versions
    • 3.8.1-1
    • 3.8.1-1ubuntu0.1~esm1
    • 3.8.1-1ubuntu0.1~esm2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • nltk Ubuntu:Pro:26.04:LTS

    Versions
    • 3.9.1-2
    • 3.9.1-2build1
    • 3.9.2-1
    • 3.9.2-1ubuntu0.1~esm1
    • 3.9.2-1ubuntu0.1~esm2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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