CVE-2026-82404 — TOON is a compact, human-readable serialization of JSON data for LLM prompts.¶
Key facts
CVE-2026-82404 is a High (8.3) vulnerability: TOON is a compact, human-readable serialization of JSON data for LLM prompts.. This entry ships a detection-only PoC and a Docker test lab.
| CVE | CVE-2026-82404 |
| Severity | High (8.3) |
| Detection / prevention | — |
| PoC | poc.py |
| Source | 2026/CVE-2026-82404/ |
Details¶
English | 한국어
Description¶
TOON is a compact, human-readable serialization of JSON data for LLM prompts. Prior to 2.3.1, decoding attacker-controlled TOON with a proto, constructor, or prototype key wrote through the object prototype chain instead of creating an own property, polluting Object.prototype for the runtime. In packages/toon/src/decode/expand.ts, the expandPaths: 'safe' path and insertPathSafe function made dotted keys such as a.proto.x the strongest vector, while plain nested objects, tabular rows, quoted keys, and streaming decode were also affected. The encoder also dropped own proto properties and could invoke an inherited setter during normalization. Services that decode untrusted TOON could experience denial of service or, when a suitable downstream gadget is present, remote code execution. This issue is fixed in version 2.3.1.
Vulnerability Details¶
| Property | Value |
|---|---|
| CVE ID | CVE-2026-82404 |
| Type | RCE |
| CVSS Score | 8.3 |
Proof of Concept¶
Download¶
# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2026/CVE-2026-82404/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-2026-82404
# 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/toon-format/toon/commit/94a2b7560b2b5ed903a4d466a3bce8b13daa2660
- https://github.com/toon-format/toon/pull/316
- https://github.com/toon-format/toon/releases/tag/v2.3.1
- https://github.com/toon-format/toon/security/advisories/GHSA-p95v-992w-h6c3
Generated by PoC Generator on 2026-09-03T03:56:23.37578906
Frequently asked questions¶
What is CVE-2026-82404?¶
CVE-2026-82404 is a High (8.3) vulnerability: TOON is a compact, human-readable serialization of JSON data for LLM prompts.. This entry ships a detection-only PoC and a Docker test lab.
How do I detect CVE-2026-82404?¶
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-2026-82404?¶
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.