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CVE-2026-33236: NLTK has a Downloader Path Traversal Vulnerability (AFO) - Arbitrary File Overwrite

• Severity: high (CVSS 8.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-03-20 · updated 2026-07-21
• Weakness: CWE-22

Description

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, the NLTK downloader does not validate the `subdir` and `id` attributes when processing remote XML index files. Attackers can control a remote XML index server to provide malicious values containing path traversal sequences (such as `../`), which can lead to arbitrary directory creation, arbitrary file creation, and arbitrary file overwrite. Commit 89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a patches the issue.

Affected products

• nltk: through 3.9.3

References

• https://github.com/nltk/nltk/commit/89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a
• https://github.com/nltk/nltk/security/advisories/GHSA-469j-vmhf-r6v7
• https://access.redhat.com/errata/RHSA-2026:10184
• https://access.redhat.com/errata/RHSA-2026:19712
• https://access.redhat.com/errata/RHSA-2026:37275
• https://access.redhat.com/errata/RHSA-2026:42644
• https://access.redhat.com/security/cve/CVE-2026-33236
• https://bugzilla.redhat.com/show_bug.cgi?id=2449824
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33236.json

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