Command Injection in Echo Go with Api Keys

Command Injection occurs when an attacker can manipulate a command executed by the operating system through unsanitized input. In an Echo Go service that relies on API keys for access control, combining external input with system command execution creates a dangerous path for attackers.

Consider an endpoint that accepts an API key as a query parameter and uses it to invoke a system command, such as retrieving service metadata or performing an administrative action. If the API key value is passed directly to a command construction function without validation or escaping, an attacker can inject additional shell commands. For example, an API key like valid_key; cat /etc/passwd could cause the server to execute both the intended command and the injected cat command, exposing sensitive files.

In Echo Go, this often manifests in handlers where the API key is used to build shell commands using string concatenation or formatting. The framework does not inherently sanitize these values, so the developer must ensure that any user-influenced data—especially API keys used for routing or authorization—is treated as untrusted input. Attackers may also probe for unauthenticated endpoints where API keys are optional, increasing the likelihood of successful injection.

Real-world attack patterns include attempts to leverage common operating system utilities to read configuration files, chain commands with logical operators, or attempt privilege escalation. Because API keys are often logged or reflected in responses, improperly handled values can also contribute to information disclosure, compounding the impact of a successful injection.

Using middleBrick to scan an Echo Go service can detect endpoints where API key inputs are reflected in command execution, highlighting risky patterns in the unauthenticated attack surface. The scan checks for input validation weaknesses and traces how external data flows into system-level operations.

Remediation focuses on eliminating direct concatenation of API keys into shell commands and enforcing strict input validation. The safest approach is to avoid invoking shell commands with external data entirely. If system operations are required, use internal Go functions or isolated execution environments rather than shell commands.

Below are examples demonstrating insecure patterns and their secure counterparts in an Echo Go handler.

Insecure Example: Using an API key directly in a shell command.

package main

import (
    "github.com/labstack/echo/v4"
    "os/exec"
    "net/http"
)

func insecureHandler(c echo.Context) error {
    apiKey := c.QueryParam("api_key")
    cmd := exec.Command("sh", "-c", "echo "+apiKey)
    out, _ := cmd.Output()
    return c.String(http.StatusOK, string(out))
}

In this example, the API key is concatenated into a shell command, enabling command injection if the key contains shell metacharacters.

Secure Example: Validating the API key and avoiding shell execution.

package main

import (
    "github.com/labstack/echo/v4"
    "net/http"
    "regexp"
)

var apiKeyPattern = regexp.MustCompile(`^[A-Za-z0-9\-_=]+\.[A-Za-z0-9\-_=]+\.?[A-Za-z0-9\-_=]*$`)

func secureHandler(c echo.Context) error {
    apiKey := c.QueryParam("api_key")
    if apiKey == "" || !apiKeyPattern.MatchString(apiKey) {
        return c.String(http.StatusBadRequest, "invalid api key")
    }
    // Use internal logic instead of shell commands
    return c.String(http.StatusOK, "key validated: "+apiKey)
}

This approach validates the API key against a strict allowlist pattern and avoids invoking a shell, effectively neutralizing command injection risks. When system-level operations are unavoidable, prefer Go’s standard library functions that do not involve a shell, and never pass concatenated user input to command arguments.

middleBrick’s scans include checks for input validation and runtime reflection of user-controlled data into command execution contexts, helping identify such patterns in your API. The tool’s LLM/AI Security checks can also detect whether API key handling logic might be inadvertently exposed in model-related endpoints.