Injection Flaws in Chi (Go)

Chi is a minimal, idiomatic Go router that relies on pattern matching and parameter extraction to dispatch requests. When user-controlled input from URLs, query strings, or headers is concatenated into handlers without validation or encoding, injection flaws can emerge. For example, building SQL or command-line arguments by string interpolation using values from chi.URLParam(r, "id") or r.URL.Query().Get("name") can lead to injection outcomes if the input is not rigorously validated.

Injection in Chi often surfaces through improper use of path parameters, query parameters, and header values. Consider an endpoint that constructs a file path or a system command using raw URL input: "reports/" + r.URL.Query().Get("file"). An attacker can traverse directories or inject shell metacharacters, leading to unauthorized file access or command execution. Chi does not sanitize inputs automatically; developers must explicitly enforce allowlists and encoding.

Another common pattern is dynamic construction of SQL queries by concatenating user input into strings. If a Chi handler builds queries like "SELECT * FROM users WHERE id = " + userID, it becomes vulnerable to SQL injection, even when using string-based parsing in Go. The same applies to NoSQL injections when constructing query filters as strings. Header-based injection is also possible when values are forwarded to logging or external systems without sanitization, enabling header smuggling or response splitting in certain gateway configurations.

Chi’s flexibility means developers are responsible for encoding outputs and validating inputs. Missing context-aware output encoding (e.g., HTML, JavaScript, URL) can lead to stored or reflected injection when data is later rendered in different contexts. Because Chi does not provide built-in sanitization, the framework can expose injection surfaces when developers assume safety without applying explicit escaping or strict schema validation.

Real-world examples align with common attack patterns such as SQL injection (CVE-2023-XXXXX-style payloads) and command injection. The OWASP API Top 10 lists injection among the most critical API risks, and Chi-based services are not immune when input handling is lax. Regular schema validation, type conversion with strict error handling, and avoiding string-based command construction are essential to reduce risk in Chi-based Go services.

Remediation focuses on strict input validation, context-aware encoding, and avoiding string concatenation for sensitive operations. Use Chi’s URL parameter extraction with explicit type conversion and validation, and prefer prepared statements or parameterized queries for database interactions.

Validate and encode URL parameters

Always validate path and query parameters against an allowlist and encode outputs based on the rendering context.

import (
    "net/http"
    "strconv"
    "strings"

    "github.com/go-chi/chi/v5"
)

func safeHandler(w http.ResponseWriter, r *http.Request) {
    idStr := chi.URLParam(r, "id")
    id, err := strconv.Atoi(idStr)
    if err != nil || id < 1 || id > 1000 {
        http.Error(w, "invalid id", http.StatusBadRequest)
        return
    }
    // Use id as integer; safe for SQL or internal logic
    _ = id
}

Use parameterized queries instead of string concatenation

For database access, use parameterized queries to eliminate SQL injection risk entirely.

import (
    "database/sql"
    "net/http"

    "github.com/go-chi/chi/v5"
)

func userHandler(db *sql.DB) http.HandlerFunc {
    return func(w http.ResponseWriter, r *http.Request) {
        userID := chi.URLParam(r, "userID")
        var name string
        err := db.QueryRow("SELECT name FROM users WHERE id = $1", userID).Scan(&name)
        if err != nil {
            http.Error(w, "not found", http.StatusNotFound)
            return
        }
        w.Write([]byte(name))
    }
}

Sanitize inputs used in commands or file paths

Never build commands or file paths by concatenating raw input. Use allowlists and the path.Clean function to prevent directory traversal.

import (
    "net/http"
    "path"
    "strings"
)

func reportHandler(w http.ResponseWriter, r *http.Request) {
    file := path.Clean("/safe/base/" + strings.TrimPrefix(chi.URLParam(r, "file"), "/"))
    if !strings.HasPrefix(file, "/safe/base/") {
        http.Error(w, "forbidden path", http.StatusBadRequest)
        return
    }
    // Proceed with safe, validated file path
    _ = file
}

Apply context-aware output encoding

When injecting data into HTML, JavaScript, or URLs, use appropriate encoding libraries to prevent injection in the target context.

import (
    "net/http"
    "github.com/microcosm-cc/bluemonday"
)

func htmlHandler(w http.ResponseWriter, r *http.Request) {
    raw := chi.URLParam(r, "comment")
    policy := bluemonday.UGCPolicy()
    safe := policy.Sanitize(raw)
    w.Write([]byte("<div>" + safe + "</div>"))
}

Leverage the CLI and continuous monitoring

Use the middlebrick CLI to scan your Chi endpoints regularly and integrate checks into your workflows. You can run middlebrick scan <url> from the terminal to detect injection-related findings and track changes over time with the Dashboard. For automated enforcement in pipelines, add the GitHub Action to fail builds when risk scores degrade, and consider the Pro plan for continuous monitoring and Slack/Teams alerts to stay ahead of regressions.