Dns Rebinding in Buffalo
How Dns Rebinding Manifests in Buffalo
DNS rebinding attacks exploit the browser's same-origin policy by tricking it into making requests to internal services via a malicious domain that resolves to both an external IP (attacker-controlled) and an internal IP (victim service). In Go-based Buffalo applications, this commonly occurs when services bind to localhost or 0.0.0.0 without proper host validation, allowing rebinding to bypass network segmentation.
Buffalo-specific vectors include:
- Dev mode servers (
buffalo dev) that listen on0.0.0.0:3000and lack Host header validation, enabling attackers to point a rebinding domain to internal services likehttp://localhost:3000. - Custom middleware or handlers that trust the
Hostheader for routing or redirect logic without whitelisting allowed domains (e.g., usingr.Hostdirectly inbuffalo.Context). - Asset pipelines or WebSocket endpoints (
github.com/gobuffalo/buffalo/websocket) that upgrade connections based on unverified origins, allowing rebinding to establish persistent channels to internal Buffalo services.
For example, a Buffalo handler using c.Request().Host to generate redirect URLs without validation could be abused: an attacker DNS-binds evil.com to 127.0.0.1, tricks a user into visiting http://evil.com, and the rebinding causes the browser to send requests to 127.0.0.1:3000 with the Host: evil.com header, which the Buffalo app might treat as trusted.
Buffalo-Specific Detection
Detecting DNS rebinding vulnerabilities in Buffalo applications requires checking for missing Host header validation and unsafe binding configurations. middleBrick identifies these risks during its unauthenticated black-box scan by:
- Testing for Host header injection: sending requests with arbitrary
Hostheaders (e.g.,Host: attacker.com) to endpoints and observing if the server reflects the header in responses (Location headers, body content, or WebSocket upgrade responses) without validation. - Checking service binding: identifying if the API is exposed on
0.0.0.0orlocalhostports without network-level restrictions, which increases rebinding risk in development or misconfigured production environments. - Analyzing WebSocket handshake responses for missing or improper
Origin validation — a common oversight in Buffalo WebSocket handlers that rebinding can exploit.
For instance, middleBrick flags a finding if a Buffalo endpoint returns a Set-Cookie or redirect URL containing the user-supplied Host header value, indicating potential rebinding susceptibility. It also checks for WebSocket endpoints that fail to validate the Origin against a trusted list, a pattern seen in apps using websocket.New without origin checks.
These findings appear in the Input Validation and Data Exposure categories, with severity based on whether the exposed internal service is sensitive (e.g., debug endpoints, admin APIs).
Buffalo-Specific Remediation
Mitigate DNS rebinding in Buffalo applications by enforcing strict Host and Origin header validation using Buffalo's built-in features. Avoid trusting user-supplied headers for security decisions.
Key fixes:
- Use
buffalo.HostMatchermiddleware to restrict allowed Host values. Example:
import (
"github.com/gobuffalo/buffalo"
"github.com/gobuffalo/buffalo/middleware"
)
func App() *buffalo.App {
app := buffalo.New(buffalo.Options{})
app.Use(middleware.HostMatcher("myapp.internal", "localhost"))
// ... routes
return app
}
This blocks requests with unexpected Host headers (like those from rebinding domains) before they reach handlers.
- For WebSocket endpoints, validate the
Origin using thewebsocket.Optionsstruct:
import (
"github.com/gobuffalo/buffalo/websocket"
"net/http"
)
func WsHandler(c buffalo.Context) error {
upgrader := websocket.New(websocket.Options{
HandshakeTimeout: 10 * time.Second,
CheckOrigin: func(r *http.Request) bool {
origin := r.Header.Get("Origin")
return origin == "https://myapp.internal" || origin == "http://localhost:3000"
},
})
return upgrader.Upgrade(c)
}
This ensures only trusted origins can establish WebSocket connections, preventing rebinding-based channel hijacking.
- In production, bind services to specific interfaces (not
0.0.0.0) and use reverse proxies (NGINX, Envoy) with strict Host validation — never rely solely on application-layer checks in exposed environments.
These fixes align with OWASP API4:2023 (Unrestricted Resource Access) by ensuring the API only processes requests from verified network contexts.