CVE-2026-78683 — NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization…¶
Key facts
CVE-2026-78683 is a Critical (9.6) vulnerability: NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization…. This entry ships a detection-only PoC and a Docker test lab.
| CVE | CVE-2026-78683 |
| Severity | Critical (9.6) |
| Detection / prevention | — |
| PoC | poc.py |
| Source | 2026/CVE-2026-78683/ |
Details¶
English | 한국어
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.
Vulnerability Details¶
| Property | Value |
|---|---|
| CVE ID | CVE-2026-78683 |
| CVSS Score | 9.6 |
Proof of Concept¶
Download¶
# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-78683/poc.py
Usage¶
# Run PoC against target
python3 poc.py --target <TARGET_URL>
# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>
⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.
Test Lab¶
This repository includes a Docker-based test environment with both vulnerable and patched applications.
Quick Start¶
# Clone and navigate to CVE directory
cd CVE-2026-78683
# Start both applications
docker-compose up -d
# Run tests
./run-tests.sh # Linux/Mac
./run-tests.ps1 # Windows PowerShell
Application Endpoints¶
| Application | URL | Status |
|---|---|---|
| Vulnerable App | http://localhost:8080 | Shows vulnerability |
| Patched App | http://localhost:8081 | Demonstrates fix |
Directory Structure¶
├── README.md # English documentation
├── README_KO.md # Korean documentation
├── poc.py # PoC detection script
├── docker-compose.yml # Container orchestration
├── run-tests.sh # Linux/Mac test runner
├── run-tests.ps1 # Windows test runner
├── vulnerable-app/ # Vulnerable version
│ ├── app.py
│ ├── Dockerfile
│ └── requirements.txt
└── patched-app/ # Fixed version
├── app.py
├── Dockerfile
└── requirements.txt
References¶
- https://github.com/nltk/nltk/security/advisories/GHSA-rhp5-r9x4-f5g2
- https://www.vulncheck.com/advisories/nltk-before-remote-code-execution-via-unsafe-pickle-deserialization
Generated by PoC Generator on 2026-08-25T12:30:48.041450157
Frequently asked questions¶
What is CVE-2026-78683?¶
CVE-2026-78683 is a Critical (9.6) vulnerability: NLTK before 3.10.0 (affected versions <=3.9.4) contains an unsafe pickle deserialization…. This entry ships a detection-only PoC and a Docker test lab.
How do I detect CVE-2026-78683?¶
Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.
How do I block or mitigate CVE-2026-78683?¶
Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.
For authorized security testing and research only. See the full source and NVD record.