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Critical

NLTK has a Zip Slip Vulnerability

  • Disclosed: 18.02.2026
  • Updated: 11.10.2026 15:17

A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The _unzip_iter function in nltk/downloader.py uses zipfile.extractall() without performing path validation or security checks. This allows attackers to craft malicious zip packages that, when downloaded and extracted by NLTK, can execute arbitrary code. The vulnerability arises because NLTK assumes all downloaded packages are trusted and extracts them without validation. If a malicious package contains Python files, such as init.py, these files are executed automatically upon import, leading to remote code execution. This issue can result in full system compromise, including file system access, network access, and potential persistence mechanisms.

Affected software

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PlatformPackageVulnerable versionsFixed in
Python (PyPI) nltk < 3.9.3 3.9.3

References

CVSS score 10/10
CVSS vector
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Weakness (CWE)
CWE-94
Platform
Python (PyPI)
Package
nltk
Disclosed
18.02.2026
Updated
11.10.2026 15:17

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2026-96 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-7p94-766c-hgjp - 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: Uncontrolled search path when invoking the Graphviz 'dot' binary
    High · 7.8 CVE-2026-78680 < 3.10.3 3.10.3
  2. NLTK: Model-artifact APIs bypass pathsec and touch files outside allowed roots
    High · 7.0 CVE-2026-81726 <= 3.10.3 no fix
  3. NLTK: ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions
    High CVE-2026-80206 < 3.10.3 3.10.3
  4. 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
  5. 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
  6. NLTK: Corpus readers follow symlinks outside trusted roots despite pathsec enforcement
    High CVE-2026-79676 < 3.10.3 3.10.3
  7. NLTK: Corpus Reader Sandbox Bypass
    High CVE-2026-79674 < 3.10.3 3.10.3
  8. NLTK: Allowlisted pickle loaders still permit code execution in current source
    Critical CVE-2026-79657 < 3.10.3 3.10.3
  9. NLTK: Unsafe Pickle Deserialization in TransitionParser Allows Remote Code Execution
    Critical CVE-2026-78683 < 3.10.0 3.10.0
  10. NLTK: Entity-expansion DoS (billion laughs) via remaining raw ElementTree parses
    High CVE-2026-78681 < 3.10.3 3.10.3
  11. NLTK: pathsec SSRF protection can be bypassed when a proxy is configured
    High CVE-2026-78682 < 3.10.3 3.10.3
  12. 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
  13. 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
  14. NLTK: StreamBackedCorpusView Bypasses pathsec.ENFORCE - Arbitrary Local File Read
    High CVE-2026-63312 < 3.10.0 3.10.0
  15. 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
  16. NLTK: Stable FrameNet and NKJP readers parse outside-root XML
    High · 5.9 CVE-2026-62385 < 3.10.0 3.10.0
  17. NLTK: Default ENFORCE=False Disables All pathsec Security Controls
    High CVE-2026-62388 < 3.10.0 3.10.0
  18. NLTK TweetTokenizer vulnerable to denial of service through catastrophic regex backtracking
    High · 7.5 CVE-2026-72818 < 3.10.1 3.10.1
  19. 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
  20. Natural Language Toolkit (NLTK): ReDoS in NLTK ReviewsCorpusReader FEATURES regex
    High · 7.5 CVE-2026-12061 < 3.10.0 3.10.0
  21. Natural Language Toolkit (NLTK): Path Traversal in NKJPCorpusReader leads to Arbitrary File Read and bypasses the nltk.pathsec sandbox (ENFORCE=True)
    High · 7.5 CVE-2026-12072 < 3.10.0 3.10.0
  22. Natural Language Toolkit (NLTK) has path traversal in FramenetCorpusReader.frame() that allows arbitrary XML file read, bypassing the nltk.pathsec sandbox (ENFORCE=True)
    High · 7.5 CVE-2026-12074 < 3.10.0 3.10.0
  23. NLTK (Natural Language Toolkit) before version 3.9.3 contains an eval injection vulnerability in the nltk.collocations module that allows an attacker who controls command-line arguments to execute arb
    High CVE-2025-71408 < 3.9.3 3.9.3
  24. In nltk/nltk versions 3.9.3 and earlier, five Stanford interface classes (StanfordPOSTagger, StanfordNERTagger, StanfordParser, StanfordDependencyParser, and StanfordNeuralDependencyParser) are vulner
    High · 7.8 CVE-2026-12252 < 3.9.4 3.9.4
  25. NLTK version 3.9.4 is vulnerable to a path traversal attack due to an incomplete fix for GitHub Issue #3504. The `_UNSAFE_NO_PROTOCOL_RE` regex in `nltk/data.py` checks for literal `../` sequences but
    High · 7.5 CVE-2026-12243 <= 3.9.4 no fix
  26. Natural Language Toolkit (NLTK): URL-Encoded Path Traversal in nltk.data.load() Allows Arbitrary Local File Read
    High · 7.5 CVE-2026-54293 < 3.10.0 3.10.0
  27. NLTK has a Downloader Path Traversal Vulnerability (AFO) - Arbitrary File Overwrite
    High · 8.1 CVE-2026-33236 <= 3.9.2 no fix
  28. Unauthenticated remote shutdown in nltk.app.wordnet_app
    High · 7.5 CVE-2026-33231 < 3.9.4 3.9.4
  29. A vulnerability in the `filestring()` function of the `nltk.util` module in nltk version 3.9.2 allows arbitrary file read due to improper validation of input paths. The function directly opens files s
    High · 7.5 CVE-2026-0846 <= 3.9.2 no fix
  30. NLTK versions <=3.9.2 are vulnerable to arbitrary code execution due to improper input validation in the StanfordSegmenter module. The module dynamically loads external Java .jar files without verific
    Critical · 10.0 CVE-2026-0848 < 3.9.3 3.9.3
  31. A vulnerability in NLTK versions up to and including 3.9.2 allows arbitrary file read via path traversal in multiple CorpusReader classes, including WordListCorpusReader, TaggedCorpusReader, and Brack
    High · 7.5 CVE-2026-0847 < 3.9.3 3.9.3
  32. NLTK has a Zip Slip Vulnerability this entry
    Critical · 10.0 CVE-2025-14009 < 3.9.3 3.9.3
  33. ntlk unsafe deserialization vulnerability
    High · 7.5 CVE-2024-39705 < 3.9 3.9
  34. NLTK Vulnerable to REDoS
    High · 7.5 CVE-2021-3842 < 3.6.6 3.6.6
  35. Inefficient Regular Expression Complexity in nltk (word_tokenize, sent_tokenize)
    High · 7.5 CVE-2021-43854 < 3.6.6 3.6.6
  36. NLTK Vulnerable to REDoS
    High · 7.5 CVE-2021-3828 < 3.6.4 3.6.4
  37. NLTK Vulnerable To Path Traversal
    High · 7.5 CVE-2019-14751 < 3.4.5 3.4.5

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