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  3. Stored XSS in Post Body
EasyVDP10 min

Stored XSS in Post Body

By @gorka

Red social donde el cuerpo de los posts se renderiza con dangerouslySetInnerHTML, permitiendo XSS persistente que afecta a todos los usuarios que ven el post.

748 views64 completedUpdated Aug 2026
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Hunters who solved it· 8

diseo1
@diseo7 hours ago
PA2
@pa_8822 hours ago
msantiagogil183
@msantiagogil182 days ago
ER
@err0x4203 days ago
kuldeepgangwar9006
@kuldeepgangwar90064 days ago
guidoiriarte1
@guidoiriarte15 days ago
telecasacasa45
@telecasacasa455 days ago
danielmijan11
@danielmijan116 days ago

Objectives

1
Crear un post con HTML en el cuerpo
2
Verificar que el HTML se renderiza sin escapar
3
Inyectar JavaScript que se ejecuta para todos los visitantes

Information

Difficulty
Easy
Duration
10 min
Bounty
VDP
Completed
64
Creator
gorka@gorka
Updated
Aug 2026

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Tools

Navegador

Prerequisites

  • XSS stored basico
  • HTML basico

Tags

XSS

Achievement you'll earn

Solve this lab to unlock this shareable achievement

BBLABS.ESLab Solved
EasyVDP
// achievement_unlocked

Stored XSS in Post Body

XSS
Aug 2026
gorka
solved_by@gorkaMember since Mar 2026
bblabs.es// real bug bounty practice

Community writeups

Despliegue

# Opcion 1: autodeploy
./autodeploy.sh

# Opcion 2: manual
docker compose up --build

# Acceder
http://localhost:1000

Compatible con macOS, Linux y Windows (Docker Desktop / WSL).

Para parar:

./autodeploy.sh destroy
# o: docker compose down -v

Contenido del Lab

La aplicacion

Chirp con posts que soportan HTML en el cuerpo.

La vulnerabilidad

El cuerpo del post se renderiza con dangerouslySetInnerHTML sin sanitizacion. Cualquier HTML/JavaScript inyectado se ejecuta para todos los usuarios.

Cadena de ataque

1. Crear post con body: <img src=x onerror=alert('XSS')>
2. Publicar
3. Todos los que ven el post → XSS ejecutado

Solucion interactiva

Accede a /writeup dentro de la aplicacion para una guia paso a paso con botones interactivos.

Flag

(XSS persistente ejecutado)

Remediacion

  1. Sanitizar HTML con DOMPurify antes de renderizar
  2. Usar textContent o React JSX nativo
  3. CSP estricto

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