What is CVE-2026-79657?

CVE-2026-79657 is a critical-severity vulnerability in Nltk, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2026-08-25.

How severe is CVE-2026-79657?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Deserialization in Nltk

CVE-2026-79657

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.

Vulnerability class: Insecure Deserialization

Published 2026-08-25 · last modified 2026-10-08.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.013 (68.9th percentile), scored 2026-10-10.

Low probability of exploitation in the next 30 days, but still tracked. 69th percentile — 68.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.012 · newest: 0.013 · change: +0.001

Affected products

Nltk

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

github.com/nltk/nltk/security/advisories/GHSA-x99w-6fgc-pmfw (Exploit, vendor-advisory, Vendor Advisory)
www.vulncheck.com/advisories/nltk-before-3.10.3-remote-code-execution-via-unsaf… (Third Party Advisory, third-party-advisory)

Frequently asked questions

What is CVE-2026-79657?: CVE-2026-79657 is a critical-severity vulnerability in Nltk, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2026-08-25.
How severe is CVE-2026-79657?: Critical severity. CVSS v3 base score is 9.8 out of 10.