Is This vulnerability exploited in the wild?

No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

How severe is This vulnerability?

High severity, with a CVSS score of 7, published 27 August 2026.

Is there a fix for This vulnerability?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is This vulnerability attacked?

It is attacked over the network, in a software library.

Check whether you run nltk (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

NLTK path traversal in model-artifact APIs via pathsec bypass

Severity: high · CVSS 7 · Published 2026-08-27

NLTK is a natural language processing library that includes a path security (pathsec) mechanism to confine file access to approved sandbox directories. However, model loading and saving APIs for several components (TransitionParser, AveragedPerceptron, PerceptronTagger) bypass this enforcement and use raw file operations, allowing attackers to read sensitive files or write malicious files anywhere on the system if an application trusts user-supplied model paths.

Technologies: nltk (PyPI). Vendors: PyPI.

Quick answers

Is This vulnerability exploited in the wild?: No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?: High severity, with a CVSS score of 7, published 27 August 2026.
Which products and versions are affected?: nltk (PyPI) <= 3.10.3.
Is there a fix for This vulnerability?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is This vulnerability attacked?: It is attacked over the network, in a software library.
Am I affected?: Check whether you run nltk (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is a sandbox bypass (CWE-73: External Control of File Name or Path) in NLTK's model persistence APIs. Root cause: TransitionParser.train(), TransitionParser.parse(), AveragedPerceptron.save(), AveragedPerceptron.load(), PerceptronTagger.save_to_json(), and save_maxent_params() use built-in Python open() instead of nltk.pathsec.open() for file access, even when pathsec.ENFORCE=True is set. Sibling functions like PerceptronTagger.load_from_json() and load_maxent_params() correctly use pathsec-aware helpers and reject outside-root paths. Attack preconditions: the application must enable pathsec enforcement and allow untrusted workflows to specify model paths. An attacker can then supply a path with traversal sequences (e.g., ../../../etc/passwd) that bypass the sandbox. Impact: read/write of arbitrary files. No patch is currently available.

Affected products

NLTK Project NLTK <= 3.10.3

Timeline

2026-08-27: disclosed: Published by GHSA-hqj7-phwp-c3fp and associated with CVE-2026-81726
2026-08-27: advisory: Original advisory published
2026-09-02: other: GHSA-hqj7-phwp-c3fp marked as duplicate and withdrawn in favor of GHSA-8mgp-746c-j5xp

References

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