Stack Overflow in Buffalo

Stack Overflow vulnerabilities in Buffalo applications typically emerge through recursive template rendering and deeply nested context structures. Buffalo's template engine, Plush, can inadvertently create conditions where templates recursively include themselves through context variables, leading to stack exhaustion.

A common Buffalo-specific manifestation occurs when using f:yield with dynamic content sections. Consider this pattern:

// actions/posts.go
func PostsCreate(c buffalo.Context) error {
    // Recursive context injection
    c.Set("content", 
        fmt.Sprintf("<div>%s</div>", 
            c.Value("content")))
    return c.Render(200, r.HTML("posts/create.plush.html"))
}

When the template renders <%= f:yield :content %>, it creates an infinite recursion loop. Each render call adds to the Go call stack until the application crashes with a runtime: goroutine stack exceeds 1000000000 byte(s) error.

Another Buffalo-specific scenario involves context chaining in middleware. Buffalo's middleware chain processes requests sequentially, and if a middleware recursively calls c.Render() without breaking the chain, it can trigger stack overflow:

// middleware/recursive.go
func RecursiveMiddleware(next buffalo.Handler) buffalo.Handler {
    return func(c buffalo.Context) error {
        // Dangerous recursive call
        return next(c)
    }
}

When combined with route handlers that also call next or render templates, this creates deep call stacks that exceed Go's default limits.

Detecting Stack Overflow vulnerabilities in Buffalo requires both static analysis and runtime monitoring. middleBrick's black-box scanning approach is particularly effective for Buffalo applications because it tests the unauthenticated attack surface without requiring source code access.

For template recursion detection, middleBrick's Input Validation scanner specifically looks for Plush template patterns that could lead to infinite recursion. The scanner tests for:

• Dynamic f:yield content with self-referential variables
• Nested template includes with variable interpolation
• Context variable chains that could create loops
• Recursive middleware chains in the request pipeline

Runtime detection in Buffalo applications should include stack depth monitoring. You can implement middleware that tracks call stack depth:

// middleware/stackmonitor.go
import (
    "github.com/gobuffalo/buffalo"
    "runtime/debug"
)

func StackMonitor() buffalo.MiddlewareFunc {
    return func(next buffalo.Handler) buffalo.Handler {
        return func(c buffalo.Context) error {
            // Capture initial stack depth
            initial := len(debug.Stack())
            
            err := next(c)
            
            // Calculate stack growth
            final := len(debug.Stack())
            growth := final - initial
            
            if growth > 10000 { // Arbitrary threshold
                c.Logger().Warn("High stack growth detected",
                    "growth", growth)
            }
            
            return err
        }
    }
}

middleBrick's continuous monitoring (Pro plan) can automatically scan your Buffalo API endpoints on a schedule, alerting you when stack-related vulnerabilities are detected or when security scores drop due to recursion issues.

Buffalo provides several native approaches to prevent Stack Overflow vulnerabilities. The most effective strategy combines template safeguards, context management, and middleware controls.

For template recursion prevention, implement depth-limited rendering in your templates:

// templates/components/recursive.plush.html
<% depth := 0 %>
<% maxDepth := 10 %>
<% func safeRender(content string, current int) string { %>
    <% if current >= maxDepth { %>
        <% return "<div>Max recursion depth reached</div>" %>
    <% } %>
    <% return content %>
<% } %>

<% content := safeRender("<div>" + .content + "</div>", depth + 1) %>
<%= content %>

For context management, use Buffalo's context validation middleware to prevent recursive context setting:

// middleware/contextguard.go
import (
    "github.com/gobuffalo/buffalo"
    "strings"
)

type contextGuard struct {
    visited map[string]bool
}

func ContextGuard() buffalo.MiddlewareFunc {
    return func(next buffalo.Handler) buffalo.Handler {
        return func(c buffalo.Context) error {
            // Check for recursive context keys
            for _, key := range c.Keys() {
                if strings.Contains(key, "recursive") {
                    return fmt.Errorf("recursive context detected")
                }
            }
            return next(c)
        }
    }
}

For middleware chain protection, implement a depth counter:

// middleware/depthguard.go
import (
    "github.com/gobuffalo/buffalo"
)

var depthCounter = make(map[string]int)

func DepthGuard() buffalo.MiddlewareFunc {
    return func(next buffalo.Handler) buffalo.Handler {
        return func(c buffalo.Context) error {
            key := c.Request().URL.Path
            depthCounter[key]++
            
            if depthCounter[key] > 50 { // Arbitrary limit
                return fmt.Errorf("middleware depth limit exceeded")
            }
            
            defer func() {
                depthCounter[key]--
            }()
            
            return next(c)
        }
    }
}

middleBrick's GitHub Action integration can automatically scan your Buffalo application during CI/CD pipelines, ensuring these protections are in place before deployment. The action can be configured to fail builds if stack-related vulnerabilities are detected:

# .github/workflows/security.yml
name: Security Scan
on: [push, pull_request]

jobs:
  security:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Run middleBrick Scan
        run: |
          npm install -g middlebrick
          middlebrick scan https://your-buffalo-app.com/api/v1 --fail-on-severity=medium