fix(security): 会话密钥改为随机生成，修复硬编码密钥可伪造管理员会话

安全审计 P0 修复：旧版会话签名密钥硬编码在源码中（源码公开即泄露），任何人可据此伪造 isAdmin 会话接管后台。 - config: 新增 [web].secret_key，首启/升级时用 crypto/rand 自动生成 32 字节随机密钥并持久化；旧硬编码值自动替换 - config: 支持 MAILGO_SECRET_KEY 环境变量覆盖（覆盖值不落盘） - config: 配置文件权限收紧为 0600（同时保护 relay_password 等敏感字段） - web: NewWebServer 校验密钥（空/旧默认值/短于16字节拒绝启动） - test: 伪造会话拒绝、密钥生命周期（生成/持久化/重启稳定/env不落盘）等 9 个测试 - docs: README 配置参考、security_todo.md 安全修复清单部署注意：升级重启后所有用户需重新登录。
2026-08-19 16:21:28 +08:00
parent 6484af7e63
commit 551ed981de
8 changed files with 680 additions and 10 deletions
@@ -1,7 +1,10 @@
 package config

 import (
+	"crypto/rand"
+	"encoding/hex"
 	"fmt"
+	"log"
 	"os"
 	"path/filepath"
 	"runtime"
@@ -25,8 +28,25 @@ type StorageConfig struct {
 // WebConfig holds web server settings.
 type WebConfig struct {
 	Addr string `toml:"addr"`
+	// SecretKey 是 Web 会话 cookie 的签名密钥。留空时首次启动自动生成
+	// 随机密钥并持久化到配置文件；也可通过环境变量 MAILGO_SECRET_KEY
+	// 覆盖（覆盖值不落盘，适合容器部署）。
+	SecretKey string `toml:"secret_key"`
 }

+// SecretKeyEnvVar 是覆盖会话签名密钥的环境变量名。
+const SecretKeyEnvVar = "MAILGO_SECRET_KEY"
+
+// InsecureLegacySecretKey 是旧版本硬编码在源码中的会话签名密钥。
+// 源码公开意味着该密钥完全不可信，任何出现都必须替换。
+const InsecureLegacySecretKey = "mail-go-secret-key-change-in-production"
+
+// MinSecretKeyLen 是允许的最短会话密钥长度（字节）。
+const MinSecretKeyLen = 16
+
+// secretKeyRandomBytes 是自动生成密钥的随机字节数（hex 编码后 64 字符）。
+const secretKeyRandomBytes = 32
+
 // SMTPConfig holds SMTP server settings.
 type SMTPConfig struct {
 	Addr           string `toml:"addr"`
@@ -298,6 +318,63 @@ func mergeDefaults(cfg *Config, defaults *Config) *Config {
 	return cfg
 }

+// generateSecretKey generates a cryptographically random session key,
+// hex-encoded (64 characters for 32 random bytes).
+func generateSecretKey() (string, error) {
+	buf := make([]byte, secretKeyRandomBytes)
+	if _, err := rand.Read(buf); err != nil {
+		return "", fmt.Errorf("生成随机会话密钥失败: %w", err)
+	}
+	return hex.EncodeToString(buf), nil
+}
+
+// ensureSecretKey guarantees that cfg holds a trustworthy session key:
+// an empty value or the known insecure legacy default is replaced with a
+// freshly generated random key. The caller is responsible for persisting
+// the updated config.
+func ensureSecretKey(cfg *Config) error {
+	if cfg.Web.SecretKey != "" && cfg.Web.SecretKey != InsecureLegacySecretKey {
+		return nil
+	}
+	key, err := generateSecretKey()
+	if err != nil {
+		return err
+	}
+	if cfg.Web.SecretKey == InsecureLegacySecretKey {
+		log.Printf("检测到不安全的旧默认会话密钥，已自动更换为随机密钥（所有已登录会话将失效）")
+	} else {
+		log.Printf("已生成随机会话密钥并写入配置文件（Web 会话签名密钥，请妥善备份）")
+	}
+	cfg.Web.SecretKey = key
+	return nil
+}
+
+// applySecretKeyEnv lets the MAILGO_SECRET_KEY environment variable
+// override the key loaded from the config file. The override value is
+// never persisted to disk.
+func applySecretKeyEnv(cfg *Config) *Config {
+	if env := os.Getenv(SecretKeyEnvVar); env != "" {
+		cfg.Web.SecretKey = env
+	}
+	return cfg
+}
+
+// ValidateSecretKey rejects session signing keys that are missing, too
+// short, or the known insecure legacy default hardcoded in old versions.
+func ValidateSecretKey(key string) error {
+	if key == "" {
+		return fmt.Errorf("Web 会话密钥为空，拒绝启动：请检查配置文件 [web].secret_key 或环境变量 %s", SecretKeyEnvVar)
+	}
+	if key == InsecureLegacySecretKey {
+		return fmt.Errorf("Web 会话密钥为已知不安全的旧默认值，拒绝启动：请删除配置文件 [web].secret_key 后重启以自动生成随机密钥")
+	}
+	if len(key) < MinSecretKeyLen {
+		return fmt.Errorf("Web 会话密钥过短（%d 字节，最少 %d）：请检查 %s 或 [web].secret_key",
+			len(key), MinSecretKeyLen, SecretKeyEnvVar)
+	}
+	return nil
+}
+
 // writeConfig writes the configuration to the given file path.
 // It creates the parent directories if they don't exist.
 func writeConfig(path string, cfg *Config) error {
@@ -316,6 +393,11 @@ func writeConfig(path string, cfg *Config) error {
 	if err := enc.Encode(cfg); err != nil {
 		return fmt.Errorf("写入配置文件失败: %w", err)
 	}
+
+	// 配置文件包含会话密钥、中继密码等敏感信息，收紧为仅属主可读写
+	if err := os.Chmod(path, 0600); err != nil {
+		return fmt.Errorf("设置配置文件权限失败 %s: %w", path, err)
+	}
 	return nil
 }

@@ -323,15 +405,23 @@ func writeConfig(path string, cfg *Config) error {
 // If the configuration file does not exist, it creates one with default values.
 // If the file exists but has missing fields, they are filled with defaults and the file is updated.
 func LoadConfig() (*Config, error) {
-	path := configFilePath()
+	return loadConfigFrom(configFilePath())
+}
+
+// loadConfigFrom implements LoadConfig against an explicit file path so it
+// can be unit-tested with temporary directories.
+func loadConfigFrom(path string) (*Config, error) {
 	defaults := defaultConfig()

 	// If config file doesn't exist, create it with defaults
 	if _, err := os.Stat(path); os.IsNotExist(err) {
+		if err := ensureSecretKey(defaults); err != nil {
+			return nil, err
+		}
 		if mkErr := writeConfig(path, defaults); mkErr != nil {
 			return nil, mkErr
 		}
-		return defaults, nil
+		return applySecretKeyEnv(defaults), nil
 	}

 	// Read existing config file
@@ -351,6 +441,11 @@ func LoadConfig() (*Config, error) {
 		cfg.Outbound.RelayStartTLS = defaults.Outbound.RelayStartTLS
 	}

+	// 会话密钥缺失或不安全时补发随机密钥（随下面的写回一并落盘）
+	if err := ensureSecretKey(cfg); err != nil {
+		return nil, err
+	}
+
 	// Merge defaults for any missing fields
 	merged := mergeDefaults(cfg, defaults)

@@ -360,5 +455,5 @@ func LoadConfig() (*Config, error) {
 		return nil, writeErr
 	}

-	return merged, nil
+	return applySecretKeyEnv(merged), nil
 }
@@ -0,0 +1,191 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestGenerateSecretKey(t *testing.T) {
+	key, err := generateSecretKey()
+	if err != nil {
+		t.Fatalf("generateSecretKey() error: %v", err)
+	}
+	// 32 随机字节 hex 编码 = 64 字符
+	if len(key) != secretKeyRandomBytes*2 {
+		t.Fatalf("key length = %d, want %d", len(key), secretKeyRandomBytes*2)
+	}
+
+	// 两次生成必须不同
+	key2, err := generateSecretKey()
+	if err != nil {
+		t.Fatalf("generateSecretKey() error: %v", err)
+	}
+	if key == key2 {
+		t.Fatal("generated keys must be unique")
+	}
+
+	if key == InsecureLegacySecretKey {
+		t.Fatal("generated key must never equal the legacy insecure default")
+	}
+}
+
+func TestLoadConfigFirstBootGeneratesSecretKey(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "mail_go.toml")
+
+	cfg, err := loadConfigFrom(path)
+	if err != nil {
+		t.Fatalf("loadConfigFrom() error: %v", err)
+	}
+	if cfg.Web.SecretKey == "" {
+		t.Fatal("secret key should be generated on first boot")
+	}
+
+	// 密钥必须落盘，保证重启后会话不失效
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("read config file: %v", err)
+	}
+	if !strings.Contains(string(data), "secret_key = \""+cfg.Web.SecretKey+"\"") {
+		t.Fatalf("generated secret key should be persisted, file content:\n%s", data)
+	}
+
+	// 第二次加载返回相同密钥（会话保持）
+	cfg2, err := loadConfigFrom(path)
+	if err != nil {
+		t.Fatalf("second loadConfigFrom() error: %v", err)
+	}
+	if cfg2.Web.SecretKey != cfg.Web.SecretKey {
+		t.Fatalf("secret key must be stable across restarts: %q != %q", cfg2.Web.SecretKey, cfg.Web.SecretKey)
+	}
+
+	// 配置文件包含敏感信息，权限必须为 0600（Windows 无 POSIX 权限，跳过）
+	if runtime.GOOS != "windows" {
+		info, err := os.Stat(path)
+		if err != nil {
+			t.Fatalf("stat config file: %v", err)
+		}
+		if perm := info.Mode().Perm(); perm != 0600 {
+			t.Fatalf("config file mode = %o, want 0600", perm)
+		}
+	}
+}
+
+func TestLoadConfigBackfillsSecretKey(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "mail_go.toml")
+
+	// 模拟旧版本升级：配置文件中没有 secret_key 字段
+	old := "[web]\naddr = \":9090\"\n\n[smtp]\ndomain = \"example.com\"\n"
+	if err := os.WriteFile(path, []byte(old), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	cfg, err := loadConfigFrom(path)
+	if err != nil {
+		t.Fatalf("loadConfigFrom() error: %v", err)
+	}
+	if cfg.Web.SecretKey == "" {
+		t.Fatal("missing secret key should be backfilled")
+	}
+	// 原有字段保持不变
+	if cfg.Web.Addr != ":9090" {
+		t.Fatalf("existing field overwritten: addr = %q", cfg.Web.Addr)
+	}
+	if cfg.SMTP.Domain != "example.com" {
+		t.Fatalf("existing field overwritten: domain = %q", cfg.SMTP.Domain)
+	}
+}
+
+func TestLoadConfigReplacesLegacySecretKey(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "mail_go.toml")
+
+	content := "[web]\naddr = \":8080\"\nsecret_key = \"" + InsecureLegacySecretKey + "\"\n"
+	if err := os.WriteFile(path, []byte(content), 0644); err != nil {
+		t.Fatal(err)
+	}
+
+	cfg, err := loadConfigFrom(path)
+	if err != nil {
+		t.Fatalf("loadConfigFrom() error: %v", err)
+	}
+	if cfg.Web.SecretKey == InsecureLegacySecretKey {
+		t.Fatal("legacy insecure secret key must be replaced")
+	}
+	if cfg.Web.SecretKey == "" {
+		t.Fatal("replacement key must be non-empty")
+	}
+
+	// 替换后的密钥必须落盘
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(string(data), InsecureLegacySecretKey) {
+		t.Fatal("legacy key should be removed from the config file")
+	}
+	if !strings.Contains(string(data), cfg.Web.SecretKey) {
+		t.Fatal("replaced key should be persisted")
+	}
+}
+
+func TestSecretKeyEnvOverride(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "mail_go.toml")
+
+	// 先正常生成一个落盘密钥
+	cfg1, err := loadConfigFrom(path)
+	if err != nil {
+		t.Fatalf("first loadConfigFrom() error: %v", err)
+	}
+
+	// 环境变量覆盖运行时密钥
+	envKey := "env-override-secret-key-0123456789abcdef"
+	t.Setenv(SecretKeyEnvVar, envKey)
+
+	cfg2, err := loadConfigFrom(path)
+	if err != nil {
+		t.Fatalf("second loadConfigFrom() error: %v", err)
+	}
+	if cfg2.Web.SecretKey != envKey {
+		t.Fatalf("env var should override the file key: got %q", cfg2.Web.SecretKey)
+	}
+
+	// 环境变量的值不能落盘
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if strings.Contains(string(data), envKey) {
+		t.Fatal("env-provided secret must not be persisted to disk")
+	}
+	// 落盘密钥保持原值
+	if !strings.Contains(string(data), cfg1.Web.SecretKey) {
+		t.Fatal("file key should remain unchanged when env override is active")
+	}
+}
+
+func TestValidateSecretKey(t *testing.T) {
+	cases := []struct {
+		name    string
+		key     string
+		wantErr bool
+	}{
+		{"empty", "", true},
+		{"legacy default", InsecureLegacySecretKey, true},
+		{"too short", "short", true},
+		{"valid hex key", "0123456789abcdef0123456789abcdef", false},
+		{"valid env style", "env-override-secret-key-0123456789abcdef", false},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			err := ValidateSecretKey(tc.key)
+			if tc.wantErr && err == nil {
+				t.Fatalf("expected error for key %q", tc.key)
+			}
+			if !tc.wantErr && err != nil {
+				t.Fatalf("unexpected error for key %q: %v", tc.key, err)
+			}
+		})
+	}
+}