# NLTK: Allowlisted pickle loaders still permit code execution in current source

Advisory record · `GHSA-x99w-6fgc-pmfw`

- **Identifiers:** `GHSA-x99w-6fgc-pmfw` · `CVE-2026-79657` · `PYSEC-2026-3735`
- **State:** Confirmed
- **Severity:** CVSS 9.3 Critical
- **Critical:** Yes: CVSS 9+
- **Weakness (CWE):** [CWE-502](https://cwe.mitre.org/data/definitions/502.html) · [CWE-693](https://cwe.mitre.org/data/definitions/693.html)
- **Tags:** [Insecure deserialization](https://agentprime.io/advisories/tag/deserialization.md) · [CWE-693](https://agentprime.io/advisories/tag/cwe-693.md)
- **Published:** 8 Sept 2026
- **Updated:** 8 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 8 Sept 2026, 16:42 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Critical

Critical, because:

- CVSS score 9.3: 9.0 or more.

How we decide what’s critical: <https://agentprime.io/advisories/critical.md>

## Affected packages

- `nltk` (PyPI): affected `<3.10.3`; fixed in `3.10.3`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 9.3 Critical, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`, from CNA (VulnCheck)

- **CISA KEV:** Not listed.
- **EPSS:** 0.013, the 69th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:38 UTC: First seen by agentprime
- 31 Oct 2026, 14:38 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-x99w-6fgc-pmfw)

## Sources

- [GitHub Advisory Database: GHSA-x99w-6fgc-pmfw](https://github.com/advisories/GHSA-x99w-6fgc-pmfw)
- [OSV: GHSA-x99w-6fgc-pmfw](https://osv.dev/vulnerability/GHSA-x99w-6fgc-pmfw)
- <https://github.com/nltk/nltk/security/advisories/GHSA-x99w-6fgc-pmfw>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-79657>
- <https://github.com/nltk/nltk/commit/c3e37113742a1ebeeb4f2ca58941f320f98805ea>
- <https://github.com/nltk/nltk>
- <https://github.com/nltk/nltk/releases/tag/v3.10.3>
- <https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3735.yaml>
- <https://www.vulncheck.com/advisories/nltk-before-3.10.3-remote-code-execution-via-unsafe-pickle-deserialization>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-x99w-6fgc-pmfw>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

---

The web page: <https://agentprime.io/advisories/GHSA-x99w-6fgc-pmfw/>. Everything for agents: <https://agentprime.io/llms.txt>.