high CVSS 8.8

CVE-2025-14009·Python vulnerability

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.

Severity
high
Software
Python
Fixed in
3.9.3
Published
2026-02-18

Affected versions

Until: 3.9.3

Fixed in: 3.9.3

How to fix this CVE

Update Python and NLTK to the latest patched versions immediately, as CVE-2025-14009 allows remote code execution through malicious package extraction. Upgrade to NLTK 3.9.3 or later, which validates zip file contents before extraction. Review your NLTK data directory for any suspicious files and consider reinstalling all NLTK data packages after patching.

sudo dnf update python3 python3-nltk

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Check your NLTK version with `python3 -c "import nltk; print(nltk.__version__)"`
  2. Step 2: Verify the downloader component is being used by checking if nltk.download() calls exist in your application code: `grep -r "nltk.download" /path/to/app`
  3. Step 3: Examine NLTK data directory for unexpected Python bytecode or .pyc files: `find ~/nltk_data -name '*.pyc' -o -name '__pycache__'` and note timestamps
  4. Step 4: Confirm the patch is installed by verifying NLTK version is 3.9.3 or later: `python3 -c "import nltk; assert nltk.__version__ >= '3.9.3', 'Vulnerable version'"`

FAQ

What is CVE-2025-14009?

CVE-2025-14009 is a remote code execution vulnerability in NLTK's package downloader that fails to validate zip file contents before extraction, allowing attackers to inject malicious Python modules that execute automatically when imported.

Is CVE-2025-14009 being actively exploited?

No, this vulnerability is not currently listed on CISA's Known Exploited Vulnerabilities catalog, and no public exploits are available, though the risk remains high due to the severity of the flaw.

What versions of Python are affected by CVE-2025-14009?

All NLTK versions up to and including 3.9.2 are affected. The vulnerability exists regardless of the Python version used, as the flaw is in the NLTK library itself, not the Python interpreter.

How do I check if my server is vulnerable to CVE-2025-14009?

Run `python3 -c "import nltk; print(nltk.__version__)"` and compare the version against 3.9.3—if your version is lower, you are vulnerable and should upgrade immediately.

Does Defensia detect CVE-2025-14009?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Python and NLTK are installed on a monitored server, CVE-2025-14009 will appear in your dashboard with remediation steps.

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References

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