FlaskBB: SSRF in get_image_info() via unrestricted avatar URL

###Summary A Server-Side Request Forgery (SSRF) vulnerability in get_image_info() allows any authenticated user to force the server to send HTTP requests to arbitrary internal endpoints, including cloud metadata services (e.g., AWS 169.254.169.254). This is a blind SSRF with confirmed internal port scanning and internal API triggering capabilities. CVSS 6.5 Medium.

###Details In flaskbb/utils/helpers.py (line 571), the url parameter is passed directly to requests.get(url, stream=True) without any validation of scheme, host, or IP address.

python# flaskbb/utils/helpers.py:571
def get_image_info(url: str):
    r = requests.get(url, timeout=(3.05, 27), stream=True)

Attack chain:

POST /user/settings/user-details (avatar URL)
→ ValidateAvatarURL.validate()    # validators.py:103
→ check_image(avatar)             # helpers.py:628
→ get_image_info(url)             # helpers.py:571
→ requests.get(url)               # No domain/IP restriction
Entry points:

/user/settings/user-details (any authenticated user)
/admin/users/<id>/edit (admin only)

###PoC submit.zip

Log in to FlaskBB as any user Navigate to Settings → User Details Enter http://169.254.169.254/latest/meta-data/ as the avatar URL Submit the form The server sends a GET request to the internal metadata endpoint

Three exploitation channels confirmed:

Server-side request: Captured on mock metadata server Internal port scan: check_image() returns distinct errors (CONN_REFUSED, NO_CONTENT_LENGTH, TYPE_NOT_ALLOWED, SUCCESS) that map internal network topology Internal API triggering: Mock APIs on 127.0.0.1:9200 triggered via SSRF (deploy, shutdown, key dump endpoints)

###Impact Any authenticated user is impacted. Attackers can force the server to request internal services, cloud metadata endpoints, or private network resources. On cloud deployments (AWS/GCP/Azure), IAM credentials can be leaked. In production, any GET-triggered internal service is reachable: CI/CD webhooks, Elasticsearch, etcd, Consul, etc.