CVE-2025-14009: NLTK has a Zip Slip Vulnerability

Should you act?

Normal patch cycle

No exploitation signal; fix it in your next routine update if you are affected. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 1.0%, percentile 64: FIRST’s model estimates a 1.0% chance of exploitation activity in the next 30 days, higher than 64% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Needs an account (low (any account)). Exposure depends on who can log in.
• Only applies if your dependency tree includes nltk (PyPI) <= 3.9.2, fixed in 3.9.3. Check your lockfile, including transitive dependencies.

What it is

A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The unzipiter 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.

From the GitHub advisory

A critical vulnerability exists in the NLTK downloader component of nltk/nltk, affecting all versions. The unzipiter 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.

Weakness type: CWE-94.

Product: nltk (PyPI) · Assigned by: @huntr_ai · Published: 2026-02-18

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: low (any account)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.04% probability of exploitation activity in the next 30 days; percentile 64.

Timeline

• 2026-02-18 — CVE record published by @huntr_ai
• 2026-02-18 — GitHub-reviewed advisory GHSA-7p94-766c-hgjp published (critical)
• 2026-07-15 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. access.redhat.com access.redhat.com

Vulnerability records

1. GitHub Advisory GHSA-7p94-766c-hgjp github.com
2. CVE.org record CVE-2025-14009 cve.org
3. NVD entry CVE-2025-14009 nvd.nist.gov

Other references from the CVE record and advisory

1. huntr.com huntr.com
2. access.redhat.com access.redhat.com
3. RHBZ#2440724 bugzilla.redhat.com
4. security.access.redhat.com security.access.redhat.com
5. github.com github.com
6. github.com github.com
7. github.com github.com
8. github.com github.com

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