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  3. Blind SSRF with Internal Headers
HardVDP30 min

Blind SSRF with Internal Headers

By @gorka

Plataforma de archivos con importacion remota que realiza peticiones server-side pero no devuelve la respuesta. Los headers internos (incluyendo la flag) se envian en la peticion y son visibles desde el servidor del atacante.

232 views18 completedUpdated Aug 2026
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Hunters who solved it· 8

CR1
@crash3 days ago
itrox2
@itrox5 days ago
flyingwhales3
@flyingwhales8 days ago
AL
@alex.burja.200029 days ago
SU
@suraxddqJun 2026
pl4nkton
@pl4nktonJun 2026
benjaminnocervigni
@benjaminnocervigniJun 2026
gorka
@gorkaJun 2026

Objectives

1
Usar la funcionalidad de Remote File Import
2
Notar que la respuesta no se devuelve (blind)
3
puntar a un servidor propio o al inspector integrado
4
Leer los headers internos de la peticion que contienen la flag

Information

Difficulty
Hard
Duration
30 min
Bounty
VDP
Completed
18
Creator
gorka@gorka
Updated
Aug 2026

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Tools

CurlWebhook

Prerequisites

  • SSRF blind
  • Servidor HTTP propio o webhook.site

Tags

SSRF

Achievement you'll earn

Solve this lab to unlock this shareable achievement

BBLABS.ESLab Solved
HardVDP
// achievement_unlocked

Blind SSRF with Internal Headers

SSRF
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:2000

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

Para parar:

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

Contenido del Lab

La aplicacion

FileForge con funcionalidad de importacion remota de archivos.

La vulnerabilidad

Remote File Import hace fetch server-side con headers internos incluyendo X-Internal-Flag. La respuesta del fetch no se devuelve al usuario (blind), pero los headers se envian al servidor destino.

Cadena de ataque

1. Usar Remote File Import con URL propia
2. Recibir peticion en el servidor
3. Leer headers: X-Internal-Flag contiene la flag
4. Alternativa: usar inspector integrado de la app

Solucion interactiva

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

Flag

5ebe2294ecd0e0f08eab7690d2a6ee69

Remediacion

  1. No incluir headers internos en peticiones a URLs de usuario
  2. Whitelist de dominios permitidos
  3. Bloquear localhost y rangos privados
  4. Proxy dedicado sin headers internos

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Email
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