CVE-2026-78683
NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
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.
- Affected
- nltk
- CVSS v4.0 VULNCHECK
- 9.4 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - CVSS v4.0 GitHub
- 9.4 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H - CVSS v3.1 VULNCHECK
- 9.6 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H - EPSS
- 0.51% chance of exploitation in the next 30 days, 42nd percentile
- Published
- 2026-08-25
Proof-of-concept exploits (2)
- advisories/GHSA-rhp5-r9x4-f5g2
- kinryulabs/research-pocs0★ · 2026-10-01
Security advisories
- nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2
- https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-…