Integer Overflow in Buffalo with Dynamodb

An integer overflow in a Buffalo application that interacts with DynamoDB can occur when user-supplied numeric input is used to calculate capacity, batch sizes, or pagination limits without proper validation. In Go, integers have fixed widths; for example, using int (architecture-dependent) or int32 can wrap around when values exceed their max (e.g., 2,147,483,647 for int32). If an attacker sends a crafted query parameter such as limit=2147483647 and the server adds a large offset, the sum can overflow, resulting in a small or zero value after wrapping. Because DynamoDB operations often use these integers for Limit, ExclusiveStartKey pagination, or batch request sizes, the overflow can cause unexpected behavior: skipped items, repeated reads, or even enumeration of unintended data when combined with misaligned pagination logic.

In a Buffalo app, routes that accept numeric pagination parameters (e.g., /api/users?limit=100&offset=0) may pass these values directly to DynamoDB via the AWS SDK. If input is not validated, an overflowed limit can produce a zero effective limit; DynamoDB may then apply its own service-side limits, or the SDK may generate a large request that stresses backend capacity. Because DynamoDB does not inherently detect application-level integer semantics, it will process the wrapped integer, potentially enabling data exposure through excessive reads or bypassing intended throttling controls. This pattern is especially risky when combined with unbounded item sizes or non-validated filter expressions, as attackers can probe how wrapped values affect result sets.

Consider an endpoint that computes a page token using integer arithmetic. If the token is derived from an overflowed counter, two different logical pages may map to the same token, causing duplicate or missing records. An attacker can exploit this to enumerate user records beyond intended access boundaries, especially if authorization checks rely on the same integer values. Since DynamoDB streams and point-in-time recovery rely on sequence numbers, unexpected wraps can also complicate auditability. The combination of Buffalo’s rapid prototyping style and DynamoDB’s flexible query patterns increases the chance that unchecked numeric inputs propagate into unsafe API behavior.

To mitigate integer overflow risks, validate and sanitize all numeric inputs before they reach DynamoDB operations. Use fixed-width, unsigned types where appropriate and enforce server-side limits. In Buffalo, apply validation in the controller or via a dedicated form object, and cap values to a safe range that is well below DynamoDB service limits. For pagination, prefer cursor-based tokens that are opaque and verified rather than raw integers.

// forms/user_list.go
package forms
type UserListForm struct {
  Limit  int `valid:"required,min=1,max=100"`
  Offset int `valid:"required,min=0,max=10000"`
}

// controllers/users_controller.go
func UsersList(c buffalo.Context) error {
  f := &forms.UserListForm{}
  if err := c.Bind(f); err != nil {
    return c.Render(400, r.JSON(map[string]string{"error": err.Error()}))
  }
  if err := c.Validate(f); err != nil {
    return c.Render(422, r.JSON(map[string]string{"error": "validation failed"}))
  }
  // Safe to use f.Limit and f.Offset
  return renderUsers(c, f.Limit, f.Offset)
}

// controllers/users_controller.go
import (
  "github.com/gobuffalo/buffalo"
  "github.com/golang-jwt/jwt/v5"
  "github.com/aws/aws-sdk-go/service/dynamodb"
)

func generateCursor(lastKey map[string]*dynamodb.AttributeValue) (string, error) {
  token := jwt.NewWithClaims(jwt.SigningMethodHS256, jwt.MapClaims{
    "last_key": base64.StdEncoding.EncodeToString([]byte(marshalAttr(lastKey))),
    "exp":      time.Now().Add(time.Hour).Unix(),
  })
  return token.SignedString([]byte(os.Getenv("JWT_SECRET")))
}

func parseCursor(cursor string) (map[string]*dynamodb.AttributeValue, error) {
  token, err := jwt.Parse(cursor, func(t *jwt.Token) (interface{}, error) {
    return []byte(os.Getenv("JWT_SECRET")), nil
  })
  if err != nil || !token.Valid {
    return nil, err
  }
  claims := token.Claims.(jwt.MapClaims)
  raw, _ := base64.StdEncoding.DecodeToString(claims["last_key"].(string))
  return unmarshalAttr(raw)
}

// utils/safeint.go
package utils
import "math/big"

func SafeLimit(requested int64) (int64, bool) {
  max := big.NewInt(1000) // safe cap aligned with DynamoDB best practices
  limit := big.NewInt(requested)
  if limit.Cmp(max) > 0 || limit.Sign() < 1 {
    return 0, false
  }
  return limit.Int64(), true
}

// controllers/reports_controller.go
func ReportsList(c buffalo.Context) error {
  raw := c.Params.Get("batch_size")
  if n, err := strconv.ParseInt(raw, 10, 64); err != nil {
    return c.Render(400, r.JSON(map[string]string{"error": "invalid batch_size"}))
  } else if safe, ok := utils.SafeLimit(n); !ok {
    return c.Render(422, r.JSON(map[string]string{"error": "batch_size out of range"}))
  } else {
    out, err := fetchFromDynamo(safe)
    // handle error and render
  }
  return nil
}

When integrating with DynamoDB, also ensure that request sizes and batch operations respect service quotas. Use the AWS SDK’s built-in pagination with safe integer checks rather than client-side arithmetic that is prone to overflow. For continuous monitoring, the Pro plan’s GitHub Action can enforce that numeric parameters remain within verified bounds and fail builds if unsafe patterns are introduced.