Command Injection in Chi with Api Keys

Command Injection occurs when an application passes untrusted data directly to a system shell or to an API call that executes commands. In the Go web framework Chi, this often arises when route handlers construct command arguments or shell strings using values from headers, query parameters, or request bodies. Api Keys are commonly passed in HTTP headers (e.g., Authorization: ApiKey ) and may be used to gate access or to select tenant-specific configurations. If an Api Key value or a value derived from it is forwarded to a command executor without validation or escaping, the key itself or its surrounding context can become the vector for injection.

For example, suppose a handler reads an Api Key from a header and uses it to build a command line for a backend tool that performs tenant isolation, such as a lookup script or a report generator. If the code uses Go’s exec.Command with concatenated strings or passes arguments via a shell, an attacker who can influence the Api Key (e.g., through a compromised token, a misconfigured client, or a parameter that ends up in the key) may inject additional shell operators or arguments. A payload like validkey; cat /etc/passwd or validkey && id could cause the process to execute unintended commands, leading to information disclosure or further compromise.

The risk is not in how middleBrick handles keys, but in how the application uses them. middleBrick’s scans include Input Validation and Unsafe Consumption checks that can flag endpoints where Api Key values appear in command-related parameters or logs, and the LLM/AI Security tests verify whether key-like values can influence tool calls or prompt execution paths. Because middleBrick tests unauthenticated attack surfaces, it can surface endpoints where an Api Key is accepted in an unusual or unsafe context, such as a query parameter that is later forwarded to a subprocess.

In Chi, developers should avoid building commands from request-derived values, especially from headers like Authorization. If command execution is required, use Go’s exec.Command with explicit arguments and no shell involvement, and treat Api Key values as opaque strings that must not be parsed or concatenated into command text. middleBrick’s findings can help identify endpoints where key-like inputs reach command-building code, enabling targeted remediation that keeps keys and commands strictly separate.

To prevent Command Injection when using Api Keys in Chi, ensure that Api Key values are never interpolated into shell commands and that any external process invocation uses safe argument-based APIs. Below are concrete examples showing insecure patterns and their secure alternatives.

Insecure pattern: building a command via string concatenation

// DO NOT DO THIS
func handler(w http.ResponseWriter, r *http.Request) {
    apiKey := r.Header.Get("X-API-Key")
    cmd := exec.Command("sh", "-c", fmt.Sprintf("./report.sh %s", apiKey))
    out, _ := cmd.Output()
    fmt.Fprint(w, string(out))
}

Secure pattern: explicit arguments without a shell

func handler(w http.ResponseWriter, r *http.Request) {
    apiKey := r.Header.Get("X-API-Key")
    // Pass the key as a dedicated argument; the script must read it as an argument or env var
    cmd := exec.Command("./report.sh", apiKey)
    out, err := cmd.Output()
    if err != nil {
        http.Error(w, "report failed", http.StatusInternalServerError)
        return
    }
    fmt.Fprint(w, string(out))
}

Even better, avoid passing sensitive keys as command arguments, as they may appear in process listings. Instead, use environment variables set explicitly on the command’s Env field:

func handler(w http.ResponseWriter, r *http.Request) {
    apiKey := r.Header.Get("X-API-Key")
    cmd := exec.Command("./report.sh")
    cmd.Env = append(os.Environ(), fmt.Sprintf("API_KEY=%s", apiKey))
    out, err := cmd.Output()
    if err != nil {
        http.Error(w, "report failed", http.StatusInternalServerError)
        return
    }
    fmt.Fprint(w, string(out))
}

If you must use a shell (e.g., for pipes or redirects), rigorously validate and sanitize the key, but the preferred approach is to keep keys out of shell invocations entirely. middleBrick’s Input Validation and Unsafe Consumption checks can highlight endpoints where key-like values reach command-building logic, and the LLM/AI Security probes confirm whether such values could influence tool calls or generated prompts.

For continuous assurance, use the middleBrick CLI to scan your Chi endpoints from the terminal (middlebrick scan <url>) or integrate the GitHub Action to fail builds if risky patterns are detected. The Dashboard lets you track how findings evolve over time, and the Pro plan adds continuous monitoring so that new routes or changes to key handling are assessed on a configurable schedule.