---
title: "CVE-2026-79657: NLTK: Allowlisted pickle loaders still permit code execution in current source"
url: https://erroneo.us/security/cve/CVE-2026-79657/
description: "CVE-2026-79657 (nltk (PyPI)): NLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that trust entire…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-08-25
date_modified: 2026-10-08
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-79657"
kev: false
cvss: 9.3
epss: 0.01267
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-79657: NLTK: Allowlisted pickle loaders still permit code execution in current source

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 1.3% , percentile 70: FIRST’s model estimates a 1.3% chance of exploitation activity in the next 30 days, higher than 70% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes nltk (PyPI) <= 3.10.2, fixed in 3.10.3 . Check your lockfile, including transitive dependencies.

## What it is

NLTK versions before 3.10.3 contain a remote code execution vulnerability in allowlisted pickle loaders that trust entire module namespaces instead of specific safe callables. Attackers can craft malicious pickle payloads invoking dangerous in-namespace functions like ReppTokenizer.execute and numpy.f2py.crackfortran.myeval through pickle REDUCE to execute arbitrary commands during model or tokenizer artifact loading.

## Affected packages

- PyPI `nltk` <= 3.10.2 → fixed: 3.10.3

## Affected products (CVE record)

- nltk nltk: < 3.10.3

## Severity

- VulnCheck CVSS 4.0: 9.3 `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`
- VulnCheck CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 4.0: 9.3 `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`

## Exploitation

- 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): 1.27% probability of exploitation activity in the next 30 days; percentile 70.

## Sources

- [GitHub Security Advisory (GHSA-x99w-6fgc-pmfw)](https://github.com/nltk/nltk/security/advisories/GHSA-x99w-6fgc-pmfw)
- [GitHub Advisory GHSA-x99w-6fgc-pmfw](https://github.com/advisories/GHSA-x99w-6fgc-pmfw)
- [CVE.org record CVE-2026-79657](https://www.cve.org/CVERecord?id=CVE-2026-79657)
- [NVD entry CVE-2026-79657](https://nvd.nist.gov/vuln/detail/CVE-2026-79657)
- [VulnCheck Advisory: NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization](https://www.vulncheck.com/advisories/nltk-before-3.10.3-remote-code-execution-via-unsafe-pickle-deserialization)
- [github.com](https://github.com/nltk/nltk/commit/c3e37113742a1ebeeb4f2ca58941f320f98805ea)
- [github.com](https://github.com/nltk/nltk/releases/tag/v3.10.3)
- [github.com](https://github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3735.yaml)

---
Source page: https://erroneo.us/security/cve/CVE-2026-79657/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt