Vulnerability · Published Aug 25, 2026 · Assigned by VulnCheck

CVE-2026-79657NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization

Critical 9.8

In plain English

A critical-severity unsafe deserialization in nltk from nltk. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.3% (higher than 70% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.8Critical

Exploit odds (30 days)1.3%top 30.1% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

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 & fixed versions

Ecosystem	Package	Fixed in	Advisory
Debian:12	nltk	no fix listed	DEBIAN-CVE-2026-79657
Debian:13	nltk	no fix listed	DEBIAN-CVE-2026-79657
Debian:14	nltk	3.10.3-1	DEBIAN-CVE-2026-79657
PyPI	nltk	3.10.3	GHSA-x99w-6fgc-pmfw
PyPI	nltk	3.10.3	PYSEC-2026-3735

Affected products (as reported)

Vendor	Product	Versions
nltk	nltk	0 – before 3.10.3

Weakness: CWE-502 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References

GitHub Security Advisory (GHSA-x99w-6fgc-pmfw) vendor-advisory
VulnCheck Advisory: NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization third-party-advisory