Imported from saisudhir14/claude-skills (skills/go-security/SKILL.md). Install upstream with npx skills add saisudhir14/claude-skills --skill go-security. Copyright stays with the author (MIT).

Go Security

Secure coding patterns for production Go. Covers OWASP top risks as they apply to Go.

SQL Injection Prevention

Always use parameterized queries. Never interpolate user input into SQL strings.

// Wrong: SQL injection
query := "SELECT * FROM users WHERE id = '" + id + "'"
db.Query(query)

// Correct: parameterized query
db.QueryContext(ctx, "SELECT * FROM users WHERE id = $1", id)

This applies to all database drivers. The placeholder syntax varies ($1 for postgres, ? for mysql).

Path Traversal Prevention

os.Root (Go 1.24+)

Use os.Root for scoped file access. Paths are resolved within the root directory and cannot escape it.

root, err := os.OpenRoot("/var/data/uploads")
if err != nil {
    return err
}
defer root.Close()

// Safe: "../etc/passwd" is rejected
f, err := root.Open(userProvidedFilename)
if err != nil {
    return err
}
defer f.Close()

Pre-Go 1.24

Use filepath.Clean and verify the result stays within the intended directory:

cleaned := filepath.Clean(userInput)
absPath := filepath.Join(baseDir, cleaned)

// Verify the path is still under baseDir
if !strings.HasPrefix(absPath, filepath.Clean(baseDir)+string(os.PathSeparator)) {
    return fmt.Errorf("path traversal: %s", userInput)
}

Input Validation

Validate all external input at system boundaries. Internal code can trust validated data.

func parseUserID(raw string) (int64, error) {
    id, err := strconv.ParseInt(raw, 10, 64)
    if err != nil {
        return 0, fmt.Errorf("invalid user ID %q: %w", raw, err)
    }
    if id <= 0 {
        return 0, fmt.Errorf("user ID must be positive, got %d", id)
    }
    return id, nil
}

For structured input, decode into typed structs and validate fields:

var req CreateUserRequest
if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
    http.Error(w, "invalid request body", http.StatusBadRequest)
    return
}
if err := req.Validate(); err != nil {
    http.Error(w, err.Error(), http.StatusBadRequest)
    return
}

Secrets Management

Never hardcode secrets. Never log them.

// Wrong: secret in source code
const apiKey = "do-not-hardcode-secrets"

// Wrong: secret in error message or log
slog.Info("connecting", "dsn", os.Getenv("DATABASE_URL"))

// Correct: read from environment, treat as opaque
dsn := os.Getenv("DATABASE_URL")
if dsn == "" {
    return errors.New("DATABASE_URL is required")
}
slog.Info("connecting to database") // no secret in log

Use type Secret string with a custom String() method to prevent accidental logging:

type Secret string

func (s Secret) String() string { return "[REDACTED]" }

func (s Secret) GoString() string { return "[REDACTED]" }

// The actual value is accessible via explicit conversion
dsn := string(cfg.DatabaseURL)

Cryptography

Use the standard library. Do not implement your own crypto.

import "crypto/rand"

// Generate random bytes (for tokens, nonces)
token := make([]byte, 32)
if _, err := rand.Read(token); err != nil {
    return err
}

// Do NOT use math/rand for security-sensitive values

Password Hashing

Use bcrypt or argon2. Never store passwords as plaintext or simple hashes.

import "golang.org/x/crypto/bcrypt"

// Hash a password
hash, err := bcrypt.GenerateFromPassword([]byte(password), bcrypt.DefaultCost)

// Verify a password
err := bcrypt.CompareHashAndPassword(hash, []byte(password))

HTTP Security

Timeouts

Always set timeouts on HTTP servers and clients. Default zero value means no timeout.

srv := &http.Server{
    Addr:         ":8080",
    Handler:      handler,
    ReadTimeout:  5 * time.Second,
    WriteTimeout: 10 * time.Second,
    IdleTimeout:  120 * time.Second,
}

client := &http.Client{
    Timeout: 10 * time.Second,
}

Response Headers

func securityHeaders(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("X-Content-Type-Options", "nosniff")
        w.Header().Set("X-Frame-Options", "DENY")
        w.Header().Set("Content-Security-Policy", "default-src 'self'")
        next.ServeHTTP(w, r)
    })
}

Close Response Bodies

Unclosed HTTP response bodies leak connections:

resp, err := client.Do(req)
if err != nil {
    return err
}
defer resp.Body.Close()

Dependency Scanning

Keep dependencies up to date and scan for known vulnerabilities:

# Check for known vulnerabilities (built into Go)
go install golang.org/x/vuln/cmd/govulncheck@latest
govulncheck ./...

# Update all dependencies
go get -u ./...
go mod tidy

Run govulncheck in CI. It checks your code against the Go vulnerability database and only reports vulnerabilities in functions you actually call.

Concurrency Safety

Shared mutable state without synchronization is a data race and a security risk. Use the race detector in tests:

go test -race ./...

Always run tests with -race in CI. Data races can cause memory corruption, which in certain contexts is exploitable.