Shellshock in Chi with Api Keys

Shellshock is a family of command injection vulnerabilities in Bash that can be triggered when untrusted data is passed into function exports and then used in shell commands. When API keys are handled in Chi applications without careful sanitization, they can become an attack vector if the runtime environment invokes system shells to process headers, environment variables, or logging routines.

In a Chi application, route handlers often read API keys from headers (e.g., api-key or authorization) and pass them to external utilities or system commands for validation, enrichment, or logging. If these values are interpolated into shell commands via functions like sh or bash, an attacker-supplied API key containing shell metacharacters can execute arbitrary code. For example, an API key such as abc; id # could cause the handler to run unintended commands if the input is not properly sanitized or if the code uses unsafe command construction patterns.

The risk is compounded when environment variables are used to propagate API keys to subprocesses. In Chi, it is common to read configuration and credentials from the environment; if an API key is stored in an environment variable and later used in a shell command without escaping, the Shellshock vector can be triggered through crafted environment exports. Attackers may send requests with specially crafted headers that manipulate the runtime environment to execute injected payloads during key validation or logging.

Because middleBrick scans unauthenticated attack surfaces, it can detect endpoints where API keys are accepted and identify risky patterns such as shell command construction with external data. Findings will highlight command injection risks tied to input validation and data exposure checks, emphasizing the need to avoid shell interactions with untrusted API key values.

To mitigate Shellshock risks when handling API keys in Chi, avoid invoking shell commands with untrusted input. Use pure F# functions for string manipulation and validation, and if external processes are required, pass arguments directly without shell interpretation.

Unsafe pattern with shell command interpolation

open System

let validateKeyUnsafe (apiKey: string) =
    // UNSAFE: interpolating user-controlled API key into a shell command
    let cmd = sprintf "echo Validating key: %s" apiKey
    let result = cmd |> Shell.Command.run
    result

Safe alternative: avoid shell and use built-in validation

open System

let isValidKeyFormat (apiKey: string) =
    // Validate key format without shell involvement
    System.Text.RegularExpressions.Regex.IsMatch(apiKey, "^[A-Za-z0-9\-_]{20,40}$")

let validateKeySafe (apiKey: string) =
    if isValidKeyFormat apiKey then
        // Perform validation using pure F# logic or HTTP client calls
        printfn "Key format valid"
    else
        printfn "Invalid key format"

If external commands are unavoidable, use argument arrays and avoid shell metacharacters

open System.Diagnostics

let runValidatorWithKey (apiKey: string) =
    // SAFE: passing arguments directly without shell interpolation
    let startInfo = ProcessStartInfo(
        FileName = "/usr/bin/validator",
        Arguments = sprintf "--key %s" apiKey // Ensure apiKey is sanitized
    )
    // Note: further sanitize apiKey by removing characters like ; & | $ ( ) `
    use process = Process.Start(startInfo)
    process.WaitForExit()
    process.ExitCode

Sanitization helper to remove dangerous characters

let sanitizeApiKey (apiKey: string) : string =
    // Remove characters that can enable command injection
    apiKey.Replace(";", "").Replace("|", "").Replace("&", "").Replace("`", "").Trim()

Environment variable handling

When API keys come from environment variables used in Chi configuration, avoid exporting them into shell contexts. Prefer in-memory validation and restrict environment variable usage to trusted configuration sources. If logging is required, ensure values are masked and not passed to shell-based logging utilities.

How middleBrick supports remediation

Using the CLI tool, you can run middlebrick scan <url> to identify endpoints that accept API keys and highlight command injection findings. The dashboard and GitHub Action integrations allow you to track these findings over time and fail builds when risk scores degrade, supporting continuous monitoring for Chi services.