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High

NLTK Vulnerable to REDoS

  • Disclosed: 04.01.2022
  • Updated: 11.10.2026 11:20

NLTK is vulnerable to REDoS in some RegexpTaggers used in the functions get_pos_tagger and malt_regex_tagger.

Affected software

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PlatformPackageVulnerable versionsFixed in
Python (PyPI) nltk < 3.6.6 3.6.6

References

CVSS score 7.5/10
CVSS vector
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Weakness (CWE)
CWE-1333
Platform
Python (PyPI)
Package
nltk
Disclosed
04.01.2022
Updated
11.10.2026 11:20

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2022-5 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-rqjh-jp2r-59cj - CC BY 4.0

Vulnerability history: nltk

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (52) in the archive
Total entries
52
First → latest
08.2019 09.2026
Without a fix
6
Exploited in attacks
0

Severity breakdown

  • Critical 5
  • High 32
  • Medium 13
  • Low 2

Disclosures per year

Severity:
  1. NLTK Vulnerable to REDoS this entry
    High · 7.5 CVE-2021-3842 < 3.6.6 3.6.6
  2. NLTK: Uncontrolled search path when invoking the Graphviz 'dot' binary
    High · 7.8 CVE-2026-78680 < 3.10.3 3.10.3
  3. NLTK: Model-artifact APIs bypass pathsec and touch files outside allowed roots
    High · 7.0 CVE-2026-81726 <= 3.10.3 no fix
  4. NLTK: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions
    High CVE-2026-80206 < 3.10.3 3.10.3
  5. NLTK: ReDoS in nltk.text.Text.findall() via unvalidated user-supplied regular expressions
    High · 7.5 CVE-2026-80205 < 3.10.0 3.10.0
  6. NLTK: JVM argument injection bypass via per-call options in the NLTK Stanford wrappers (incomplete fix of CVE-2026-12841)
    Critical · 9.8 CVE-2026-79675 < 3.10.3 3.10.3
  7. NLTK: Corpus readers follow symlinks outside trusted roots despite pathsec enforcement
    High CVE-2026-79676 < 3.10.3 3.10.3
  8. NLTK: Corpus Reader Sandbox Bypass
    High CVE-2026-79674 < 3.10.3 3.10.3
  9. NLTK: Allowlisted pickle loaders still permit code execution in current source
    Critical CVE-2026-79657 < 3.10.3 3.10.3
  10. NLTK: Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution
    Critical CVE-2026-78683 < 3.10.0 3.10.0
  11. NLTK: Entity-expansion DoS (billion laughs) via remaining raw ElementTree parses
    High CVE-2026-78681 < 3.10.3 3.10.3
  12. NLTK: pathsec SSRF protection can be bypassed when a proxy is configured
    High CVE-2026-78682 < 3.10.3 3.10.3
  13. NLTK AllowlistUnpickler dotted-name validation bypass allows remote code execution
    High · 8.8 CVE-2026-71513 >= 3.10.0, < 3.10.3 3.10.3
  14. NLTK: Symlink escape in CorpusReader allows arbitrary local file read outside the corpus root
    High · 6.2 CVE-2026-70626 < 3.9.4 3.9.4
  15. NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read
    High CVE-2026-63312 < 3.10.0 3.10.0
  16. NLTK: Symlink-based sandbox bypass in FramenetCorpusReader (bypasses the fix for CVE-2026-54292)
    High · 7.5 CVE-2026-62384 >= 3.10.0, < 3.10.2 3.10.2
  17. NLTK: Stable FrameNet and NKJP readers parse outside-root XML
    High · 5.9 CVE-2026-62385 < 3.10.0 3.10.0
  18. NLTK: Default ENFORCE=False Disables All pathsec Security Controls
    High CVE-2026-62388 < 3.10.0 3.10.0
  19. NLTK TweetTokenizer vulnerable to denial of service through catastrophic regex backtracking
    High · 7.5 CVE-2026-72818 < 3.10.1 3.10.1
  20. Natural Language Toolkit (NLTK): DNS-rebinding SSRF filter bypass in nltk.pathsec.urlopen (nltk.download / nltk.data.load) defeats ENFORCE mode
    High · 8.6 CVE-2026-12075 < 3.10.0 3.10.0
  21. Natural Language Toolkit (NLTK): ReDoS in NLTK ReviewsCorpusReader FEATURES regex
    High · 7.5 CVE-2026-12061 < 3.10.0 3.10.0
Show more (16) Showing 21 of 37

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