Zip Slip in Echo Go with Dynamodb

Zip Slip is a path traversal vulnerability that occurs when an application constructs file paths from user-supplied input without proper validation. In the context of an Echo Go application that interacts with Amazon DynamoDB, the risk emerges not from DynamoDB itself—since DynamoDB does not store files—but from how the application uses data retrieved from DynamoDB to build local filesystem paths. If a DynamoDB item contains a user-controlled field such as a file name or key, and that field is directly concatenated into a local path, an attacker can provide crafted input like ../../../etc/passwd to traverse directories and access or overwrite sensitive files.

Consider an Echo Go handler that retrieves an object identifier from DynamoDB and uses it to build a local file path. The handler might fetch an item with a key such as userFileKey, then join it to a base directory. If the key is untrusted and not sanitized, the resulting path can escape the intended directory. This becomes a full compromise vector when the application serves files to users or writes logs, because the malicious path can point outside the application’s intended scope. Even though DynamoDB only stores structured data, the lack of input validation on fields used in path construction turns a NoSQL data store into a component of a path traversal vulnerability.

In practice, this means an attacker could send a request that causes the Echo Go service to read arbitrary files, depending on the web server’s filesystem permissions. Because the vulnerability is in path handling rather than in DynamoDB’s API, scanning with middleBrick—which tests input validation and property authorization—can surface the issue by detecting unsafe use of user-influenced data in path logic. The scanner does not need to understand DynamoDB internals; it flags the concatenation of unchecked input into filesystem paths as a high-severity finding aligned with the OWASP API Top 10 category for path traversal and input validation weaknesses.

To remediate Zip Slip in an Echo Go service that uses DynamoDB, you must validate and sanitize any data from DynamoDB before using it in filesystem operations. Never trust values stored in DynamoDB, as they may reflect earlier unsafe client input. Use Go’s standard library functions to clean paths and enforce a strict base directory.

Below is a safe pattern using the path/filepath package to clean and restrict paths. The example shows an Echo Go handler that retrieves an item from DynamoDB, extracts a filename field, and builds a safe local path.

import (
    "fmt"
    "net/http"
    "path/filepath"
    "strings"

    "github.com/labstack/echo/v4"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb"
)

func getFileHandler(c echo.Context) error {
    // Assume we have a DynamoDB client and retrieved an item with a key field
    key := c.Param("key")
    // Example: fetch item from DynamoDB (pseudocode)
    // output, err := client.GetItem(context.TODO(), &dynamodb.GetItemInput{
    //     TableName: aws.String("Files"),
    //     Key: map[string]types.AttributeValue{
    //         "FileKey": &types.AttributeValueMemberS{Value: key},
    //     },
    // })
    // For this example, simulate a filename retrieved from DynamoDB
    filenameFromDynamoDB := "user_uploads/report.txt" // Replace with actual attribute value

    // Validate and sanitize the filename
    cleaned := filepath.Clean(filenameFromDynamoDB)
    if strings.Contains(cleaned, "..") {
        return c.String(http.StatusBadRequest, "invalid path")
    }

    // Enforce a base directory to prevent traversal
    base := "/safe/files"
    finalPath := filepath.Join(base, cleaned)
    finalPath = filepath.Clean(finalPath)
    if !strings.HasPrefix(finalPath, filepath.Clean(base)+string(filepath.Separator)) && finalPath != filepath.Clean(base) {
        return c.String(http.StatusBadRequest, "path traversal blocked")
    }

    // Proceed to read finalPath safely
    fmt.Fprintf(c.Response(), "Serving: %s", finalPath)
    return c.NoContent(http.StatusOK)
}

In this example, filepath.Clean removes redundant separators and . or .. elements, and an explicit prefix check ensures the resolved path remains within the allowed directory. You should apply similar validation to any field used in paths, including those retrieved from DynamoDB, and avoid using raw user input in filesystem operations.

Additionally, consider restricting file extensions and using a mapping from logical keys to physical files rather than direct passthrough. By treating all data from DynamoDB as untrusted and applying strict path hygiene, you eliminate the Zip Slip vector while preserving the integration between Echo Go and DynamoDB.