Injection Flaws in Chi with Basic Auth

Injection flaws in the Chi web framework become more nuanced when Basic Authentication is used for endpoint protection. Basic Auth transmits credentials in an encoded but easily reversible header, which can encourage developers to assume the endpoint is sufficiently secured. This assumption may lead to relaxed input validation, where user-controlled data such as query parameters, path segments, or headers are directly interpolated into system commands, SQL statements, or dynamic configuration values. An attacker who does not yet have credentials can still probe the unauthenticated attack surface; middleBrick scans this surface and flags injection risks independently of authentication mechanisms.

Consider a Chi endpoint that reads an SQL query parameter and passes it to a database query without sanitization:

let getUser (ctx: HttpContext) =
    let userId = ctx.Request.Query.["id"] // user-controlled
    // Unsafe: direct string interpolation into SQL
    sql"SELECT * FROM users WHERE id = {userId}" // potential SQL injection
    |> db.query

Even if this route is guarded by Basic Auth, the injection vector remains. middleBrick tests unauthenticated attack surfaces and highlights such patterns, noting that authentication does not prevent malicious payloads from being processed by the application logic. Attack patterns like SQL injection (CWE-89) and command injection (CWE-78) remain relevant when authentication is used as a thin perimeter without sanitization.

Chi encourages route composition and parameter binding, yet developers might inadvertently expose injection risks when mixing authenticated routes with dynamic data. For example, using route values directly in file system operations:

let downloadFile (ctx: HttpContext) =
    let fileName = ctx.GetRouteValue("fileName") // user-controlled
    let path = Path.Combine("/var/data", fileName) // potential path traversal
    File.ReadAllText(path)

An authenticated request can traverse directories if fileName contains sequences like ../../etc/passwd. middleBrick’s checks for Property Authorization and Input Validation highlight these issues, even when Basic Auth is present. The scanner does not assume authentication equates to safe data handling; it tests how endpoints process untrusted input after authentication has been satisfied.

Another scenario involves header-based injection when Basic Auth is used. Developers might misuse the Authorization header value in logs or downstream requests without validation:

let proxyRequest (ctx: HttpContext) =
    let authHeader = ctx.Request.Headers.["Authorization"]
    // Unsafe: using raw header in outgoing call or log
    log.Information("Proxying request with auth: {Auth}", authHeader)

If the header contains newline characters, it can facilitate HTTP response splitting or log injection. middleBrick’s Data Exposure and Input Validation checks flag unsafe consumption patterns, emphasizing that headers should be parsed and constrained before use. The scanner’s LLM/AI Security probes also check for prompt injection risks in any AI-assisted components, ensuring that injected content does not manipulate model behavior.

Remediation focuses on strict validation, parameterization, and separation of concerns. Do not rely on Basic Auth to sanitize inputs; treat authenticated requests as one layer in a defense-in-depth strategy. Use model binding, type-safe parameters, and allowlists for known-good values. middleBrick’s findings map relevant checks to OWASP API Top 10 and provide prioritized remediation guidance to reduce injection risk without implying automatic fixes.

Remediation for injection flaws in Chi with Basic Auth centers on validating and sanitizing all user-influenced data, regardless of authentication. Basic Auth should be treated as an access control mechanism, not an input sanitizer. Use explicit parsing, type conversion, and strict constraints before data is used in sensitive operations.

For the SQL example, switch from interpolated strings to parameterized queries:

let getUser (ctx: HttpContext) =
    let userId = ctx.Request.Query.["id"]
    // Safe: parameterized query
    sql"SELECT * FROM users WHERE id = @userId"
        .WithParameter("userId", userId)
        |> db.query

This ensures the userId value is treated as data, not executable SQL, mitigating SQL injection. Use system types such as Guid or int with model binding to enforce structure:

let getUser (ctx: HttpContext) =
    let! userId = ctx.BindModelAsync<Guid>("id")
    sql"SELECT * FROM users WHERE id = @userId"
        .WithParameter("userId", userId)
        |> db.query // type-safe binding

For file operations, validate and sanitize path components to prevent traversal. Use allowlists for file extensions and restrict to a base directory:

let allowedExtensions = [ ".pdf"; ".txt" ]
let downloadFile (ctx: HttpContext) =
    let fileName = ctx.GetRouteValue("fileName")
    let ext = Path.GetExtension(fileName)
    if not (List.contains ext allowedExtensions) then
        Results.BadRequest("Invalid file type")
    else
        let safeName = Path.GetFileName(fileName) // removes path segments
        let path = Path.Combine("/var/data", safeName)
        if not (path.StartsWith("/var/data")) then // additional guard
            Results.Forbidden()
        else
            File.ReadAllText(path)

When handling headers, parse and sanitize before use. Avoid logging raw Authorization headers; extract only necessary components and redact sensitive data:

let proxyRequest (ctx: HttpContext) =
    let authHeader = ctx.Request.Headers.["Authorization"]
    // Validate format and avoid raw logging
    match authHeader.ToString().Split(" ", 2) with
    | [|"Basic"; token|] ->
        // Process token safely, do not forward raw header
        Results.Ok("Authenticated")
    | _ -
> Results.BadRequest("Invalid authorization header")

middleBrick scans for these patterns in its Input Validation, Property Authorization, and Data Exposure checks, providing findings with severity and remediation guidance. The scanner helps teams identify where authentication coexists with unsafe data handling, but it does not alter code or block requests. Combine these coding practices with CI/CD integration using the middleBrick GitHub Action to fail builds if risk scores exceed your chosen threshold, and use the CLI to automate scans from the terminal.