Ssrf in Buffalo with Bearer Tokens

Server-Side Request Forgery (SSRF) in Buffalo occurs when an attacker can coerce the server into making HTTP requests to arbitrary internal or external endpoints. When Bearer Tokens are handled in Buffalo, the risk amplifies because requests often carry authentication credentials in headers. An SSRF vulnerability can expose these tokens if the application forwards requests to attacker-controlled destinations or internal metadata services, effectively leaking privileged tokens over outbound calls.

Buffalo applications that build HTTP clients dynamically and inject Authorization headers based on user input are particularly vulnerable. For example, if an endpoint accepts a URL parameter for proxying or webhook delivery, an attacker can supply an internal address like http://169.254.169.254/latest/meta-data/iam/security-credentials/ to harvest instance profile tokens. Because Bearer Tokens are often passed in headers, the SSRF-enabled outbound request will include them, granting the attacker access to cloud provider resources or internal services.

The interaction between SSRF and Bearer Tokens also matters in service-to-service communication. If your Buffalo app obtains a token from an internal identity provider and then uses that token to call downstream APIs, an SSRF vector can redirect those calls to malicious listeners. This can lead to token replay, privilege escalation, or data exfiltration. The unauthenticated attack surface scanned by middleBrick includes SSRF checks that look for endpoints that perform outbound HTTP calls with sensitive headers, including Authorization Bearer patterns.

During a scan, middleBrick’s 12 security checks run in parallel, including SSRF and Data Exposure, to detect whether endpoints with Bearer Token usage can be abused to reach internal or external destinations. The scanner cross-references OpenAPI specifications, looking for path parameters and headers that may propagate tokens into untrusted network calls. Findings include severity ratings and remediation guidance mapped to frameworks such as OWASP API Top 10 and PCI-DSS, helping you understand how SSRF with Bearer Tokens violates security boundaries.

To remediate SSRF when Bearer Tokens are involved in Buffalo, ensure that outbound HTTP requests never forward user-supplied URLs directly to the HTTP client, and never propagate Authorization headers to destinations that are not explicitly trusted. Use allowlists for hostnames and paths, avoid including tokens in outbound requests unless necessary, and isolate token handling to internal service-to-service flows that do not accept external input.

Example: Unsafe dynamic request with Bearer Token

// Unsafe: user-controlled URL and token propagation
app.Get("/proxy", func(c buffalo.Context) error {
    target := c.Param("url") // attacker-controlled
    token := c.Request().Header.Get("Authorization") // may contain Bearer token
    req, _ := http.NewRequest("GET", target, nil)
    if token != "" {
        req.Header.Set("Authorization", token)
    }
    resp, err := http.DefaultClient.Do(req)
    // ... handle response
    return c.Render(200, r.String(resp.Status))
})

Example: Safe host allowlist with selective token usage

// Safe: restrict destinations and avoid leaking tokens to untrusted hosts
var allowedHosts = map[string]bool{
    "api.example.com": true,
    "internal.service": true,
}

app.Get("/fetch", func(c buffalo.Context) error {
    target := c.Param("url")
    parsed, err := url.Parse(target)
    if err != nil {
        return c.Render(400, r.JSON(errorResponse{"invalid_url"}))
    }
    if !allowedHosts[parsed.Host] {
        return c.Render(403, r.JSON(errorResponse{"host_not_allowed"}))
    }
    // Do not reuse incoming Authorization header; use a scoped token or client certs
    req, _ := http.NewRequest("GET", parsed.String(), nil)
    req.Header.Set("Authorization", "Bearer INTERNAL_TOKEN") // fixed token for backend
    resp, err := http.DefaultClient.Do(req)
    // ... handle response
    return c.Render(200, r.String(resp.Status))
})

Example: Using environment-bound tokens without forwarding to user-supplied hosts

// Safe: token is sourced from environment and destination is constrained
func getBackendToken() string {
    return os.Getenv("BACKEND_BEARER_TOKEN")
}

app.Post("/webhook", func(c buffalo.Context) error {
    const expectedHost = "api.partner.com"
    if c.Request().Host != expectedHost {
        return c.Render(400, r.JSON(errorResponse{"host_mismatch"}))
    }
    payload, err := ioutil.ReadAll(c.Request().Body)
    if err != nil {
        return c.Render(400, r.JSON(errorResponse{"read_error"}))
    }
    req, _ := http.NewRequest("POST", "https://"+expectedHost+"/events", bytes.NewReader(payload))
    req.Header.Set("Authorization", "Bearer "+getBackendToken())
    resp, err := http.DefaultClient.Do(req)
    // ... handle response
    return c.Render(200, r.String(resp.Status))
})

These examples emphasize that SSRF remediation with Bearer Tokens in Buffalo is about strict destination allowlisting, avoiding the reflection of user input into network calls, and isolating sensitive credentials to internal or backend contexts. middleBrick’s scans can validate that such controls are present by checking for unsafe HTTP client usage and exposed Authorization headers in endpoints that accept external URLs.