Command Injection in Gorilla Mux with Dynamodb

Command Injection occurs when untrusted input is passed to system-level commands without validation or escaping. In a Go service using Gorilla Mux for routing and the AWS SDK for DynamoDB, the risk arises at the intersection: user-controlled path or query parameters intended to identify DynamoDB items are incorrectly used to construct shell commands, scripts, or helper processes. Even though the AWS SDK for DynamoDB does not execute shell commands, an application layer that builds OS commands from request data—such as constructing a aws dynamodb get-item invocation via exec.Command or a similar subprocess—introduces a classic injection vector.

With Gorilla Mux, route variables (e.g., {id}) and query parameters are extracted and passed to handlers. If a handler uses these values directly in a command string, an attacker can inject additional shell operators (e.g., &&, ||, ;, $()) to execute arbitrary OS commands. For example, an ID like value; cat /etc/passwd could lead to unauthorized file reads if the application builds a shell command. DynamoDB itself is not vulnerable to command injection; the exposure comes from insecure coding patterns around input used to invoke external processes that interact with DynamoDB.

Another scenario involves data retrieved from DynamoDB being concatenated into shell commands downstream. If a scan or query returns user-controlled content that is later used in a script or CLI call without proper sanitization, injection can occur at execution time. Because Gorilla Mux makes it straightforward to bind parameters, developers may mistakenly assume the framework handles sanitization, when in fact input validation and output encoding remain the developer’s responsibility.

The combination emphasizes the need to treat all inputs from Gorilla Mux route and query parameters as untrusted, especially when they flow into any subprocess or command construction, even if the ultimate target is a managed service like DynamoDB. Security therefore depends on avoiding shell invocation for DynamoDB operations and, if shell usage is unavoidable, applying strict allowlisting and escaping.

Remediation centers on avoiding shell command construction entirely when working with DynamoDB. Use the AWS SDK directly with parameterized API calls rather than building shell commands. Validate and type-check all Gorilla Mux variables before use, and apply principle of least privilege to the IAM role used by the service.

Example of vulnerable code that should be avoided:

import (
    "os/exec"
    "github.com/gorilla/mux"
)

func getItemHandler(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    id := vars["id"]
    // Dangerous: injecting user input into a shell command
    cmd := exec.Command("aws", "dynamodb", "get-item", "--table-name", "MyTable", "--key", id)
    out, _ := cmd.Output()
    w.Write(out)
}

Replace it with SDK-based, parameterized calls:

import (
    "context"
    "github.com/aws/aws-sdk-go-v2/aws"
    "github.com/aws/aws-sdk-go-v2/config"
    "github.com/aws/aws-sdk-go-v2/service/dynamodb"
    "github.com/gorilla/mux"
)

func getItemHandler(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    id := vars["id"]
    cfg, err := config.LoadDefaultConfig(context.TODO())
    if err != nil {
        http.Error(w, "unable to load SDK config", 500)
        return
    }
    svc := dynamodb.NewFromConfig(cfg)
    // Safe: using SDK types; id is passed as a string attribute value, not shell input
    key := map[string]types.AttributeValue{
        "Id": &types.AttributeValueMemberS{Value: id},
    }
    out, err := svc.GetItem(r.Context(), &dynamodb.GetItemInput{
        TableName: aws.String("MyTable"),
        Key:       key,
    })
    if err != nil {
        http.Error(w, err.Error(), 500)
        return
    }
    // Serialize out.Item safely for the response
    w.Header().Set("Content-Type", "application/json")
    json.NewEncoder(w).Encode(out.Item)
}

If you must invoke external tooling for legacy reasons, enforce strict allowlisting on the ID and avoid the shell:

import (
    "os/exec"
    "regexp"
    "github.com/gorilla/mux"
)

var safeID = regexp.MustCompile(`^[a-zA-Z0-9_-]{1,64}$`)

func getItemWithTooling(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)
    id := vars["id"]
    if !safeID.MatchString(id) {
        http.Error(w, "invalid id", 400)
        return
    }
    // No shell; arguments are passed directly, not concatenated
    cmd := exec.Command("aws", "dynamodb", "get-item",
        "--table-name", "MyTable",
        "--key", fmt.Sprintf(`{"Id":{"S":"%s"}}`, id))
    out, err := cmd.Output()
    if err != nil {
        http.Error(w, err.Error(), 500)
        return
    }
    w.Write(out)
}

Additional remediation steps include auditing all routes that accept parameters used in subprocesses, enabling structured logging for request context, and applying middleware to reject requests containing shell metacharacters when they are not expected. For continuous assurance, integrate the middleBrick CLI to scan from terminal and validate that no dangerous patterns remain in route handlers.