Out Of Bounds Write in Buffalo with Basic Auth

An Out Of Bounds Write in Buffalo with Basic Auth occurs when user-controlled data is used to compute a memory destination without proper bounds checking, and the endpoint is protected only by HTTP Basic Authentication. Because authentication happens at the HTTP layer, the application may parse and use headers such as Authorization before applying business-level validation. If the request body or parameters are not validated for size and type, an authenticated attacker can supply crafted input that writes beyond allocated memory structures. This combination does not inherently prevent unsafe memory operations; it only restricts access to the endpoint. The vulnerability manifests when the handler deserializes input into fixed-size buffers or structs, and the attacker sends a payload that overruns those buffers. Because Basic Auth is often perceived as sufficient protection, developers may skip deeper input validation, increasing the risk of unchecked writes. The scanner checks for missing length validation and unsafe use of buffers in request-handling code. Attack patterns include oversized JSON strings, large form fields, or unexpected content-length values that overflow stack or heap variables. Because the scan runs unauthenticated, it can still detect endpoints that accept requests with malformed or oversized bodies even when Basic Auth credentials are required, by observing how the service responds to invalid input. Remediation focuses on validating input sizes, using safe abstractions, and ensuring that authorization does not replace correctness checks.

Remediation in Buffalo centers on strict validation of request payloads regardless of the presence of Basic Auth. Always treat the Authorization header as an access control signal, not a correctness mechanism. Validate content length, enforce strict type checks, and use bounded data structures. Prefer strongly typed forms or JSON unmarshaling with explicit field constraints. The following code examples illustrate secure handling with Basic Auth in a Buffalo application.

Example 1: Validating Content Length and Types with Basic Auth

// handlers/app.go
package handlers

import (
    "net/http"
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/buffalo/middleware"
    "github.com/gobuffalo/packr/v2"
    "github.com/pkg/errors"
)

func SafeEndpoint(c buffalo.Context) error {
    const maxBodySize = 1024
    // Enforce a maximum request body size before parsing
    lr := &io.LimitedReader{R: c.Request().Body, N: maxBodySize}
    defer c.Request().Body.Close()
    body, err := ioutil.ReadAll(lr)
    if err != nil {
        return c.Render(413, r.JSON(map[string]string{"error": "request too large"}))
    }
    if int64(len(body)) > maxBodySize {
        return c.Render(413, r.JSON(map[string]string{"error": "request exceeds size limit"}))
    }

    // Basic Auth check (access control)
    user, pass, ok := c.Request().BasicAuth()
    if !ok || !isValidUser(user, pass) {
        return c.Render(401, r.JSON(map[string]string{"error": "unauthorized"}))
    }

    // Parse and validate business data
    var payload struct {
        Name  string `json:"name" validate:"required,max=64"`
        Value int    `json:"value" validate:"min=0,max=1000"`
    }
    if err := json.Unmarshal(body, &payload); err != nil {
        return c.Render(400, r.JSON(map[string]string{"error": "invalid json"}))
    }
    c.Set(&payload)
    return c.Render(200, r.JSON(c.Params()))
}

func isValidUser(user, pass string) bool {
    // Replace with secure credential store check
    return user == "admin" && pass == "correct-hash"
}

Example 2: Using Form Validation to Prevent Bounds Overflow

// handlers/profile.go
package handlers

import (
    "github.com/gobuffalo/buffalo"
    "github.com/gobuffalo/buffalo/middleware/paramdecoder"
    "github.com/gobuffalo/validate/v3"
)

type ProfileUpdate struct {
    Email string `validate:"required,email,max=254"`
    Bio   string `validate:"max=500"`
}

func UpdateProfile(c buffalo.Context) error {
    decoder := paramdecoder.New(paramdecoder.WithDecoder(¶mdecoder.JSONDecoder{}))
    profile := &ProfileUpdate{}
    if err := decoder.Decode(profile, c.Params()); err != nil {
        return c.Render(400, r.JSON(map[string]string{"error": "invalid payload"}))
    }

    // Enforce strict size limits on strings
    if len(profile.Email) > 254 {
        return c.Render(400, r.JSON(map[string]string{"error": "email too long"}))
    }
    if len(profile.Bio) > 500 {
        return c.Render(400, r.JSON(map[string]string{"error": "bio too long"}))
    }

    // Optional: Basic Auth for admin operations
    user, pass, ok := c.Request().BasicAuth()
    if !ok || !isValidUser(user, pass) {
        return c.Render(401, r.JSON(map[string]string{"error": "unauthorized"}))
    }

    // Safe processing
    return c.Render(200, r.JSON(map[string]string{"status": "updated"}))
}

Key remediation steps include setting explicit size limits on request bodies, validating field lengths and types before use, and avoiding direct copying of user input into fixed-size buffers. Basic Auth should be treated as an access control layer, not a safeguard against malformed input. The scanner can detect missing bounds checks and unsafe memory operations even when Basic Auth is in use.