Reference page — cumulative record through Sunday, October 4, 2026 UTC. Reference pages update as the archive grows; only dated daily editions are immutable pages of record.

CVE-2026-78683

CVE-2026-78683CRITICAL

NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization

  AV  AC  AT  PR  UI  VC  VI  VA   CVSS    EPSS   %ile   KEV
   N   L   N   N   P   H   H   H    9.4   .0051   41.4     —

AFFECTED
  Product  Versions     Fixed
  nltk     unspecified  3.10.0

TIMELINE
  Aug 25  Reserved by VulnCheck
  Aug 25  Published (CNA: VulnCheck)
  Aug 31  EXPLOIT PUBLISHED — CVE-2026-78683 (nltk). Public exploit reference added.

CWE-502 · CNA: VulnCheck · CVSS v4.0 · 2 references · NVD status: Analyzed

Description

NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization vulnerability in the TransitionParser.parse() method (nltk/parse/transitionparser.py). The method calls pickle_load() with the default restricted=False, routing deserialization through WarningUnpickler, which does not override find_class() and therefore permits arbitrary class resolution. When an application loads an attacker-crafted model file, embedded pickle gadget chains execute arbitrary Python code with the privileges of the user running the application. NLTK provides a RestrictedUnpickler for safe deserialization, but it is not used by production code paths. Fixed in 3.10.0.

Lifecycle

Complete event history — 3 events, chronological
Date	Event	Detail
August 25, 2026	Reserved	Reserved by VulnCheck
August 25, 2026	Published	Published (CNA: VulnCheck)
August 31, 2026	EXPLOIT PUBLISHED	EXPLOIT PUBLISHED — CVE-2026-78683 (nltk). Public exploit reference added.

Affected

Affected products and packages — 1 row
Vendor	Product / Package	Ecosystem	Version introduced	Fixed
nltk	nltk	—	—	3.10.0

Weaknesses

CWE-502

References (2)

https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2 [Exploit, Vendor Advisory]
https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization [Third Party Advisory]

Authoritative record: CVE-2026-78683 at cve.org

Vendors: nltk

Weaknesses: CWE-502

About this page

This is a reference page, not a dated page of record. It assembles the complete lifecycle of CVE-2026-78683 from the CVE Program record, NVD enrichment, the CISA KEV catalog, EPSS, and OSV advisories. The box score's numbers (CVSS, EPSS, KEV status) are current as of Sunday, October 4, 2026 UTC and are re-derived as the archive grows; only dated daily editions are immutable pages of record. The authoritative source for this identifier is cve.org.