fix(security): Kritische Sicherheitslücken beheben (SEC-01/02/03/05/08/17/22/26/28)

- SEC-01: Privilege Escalation verhindert — Rollenhierarchie in Create/Update/DeleteUser
- SEC-02: Tenant-Isolation in Update/DeleteUser — domain_admin nur eigene Nutzer
- SEC-03: IMAP/POP3 Owner-Check via auth.HasRole statt direktem String-Vergleich
- SEC-05: Export PDF/ZIP prüft Tenant-Zugehörigkeit vor Dateiausgabe
- SEC-08: HKDF-SHA256 trennt JWT-Secret von AES-Key (archivmail-jwt-v1 / archivmail-aes-v1)
- SEC-17: handleSecurityFix erfordert requireRole(superadmin)
- SEC-22: Mail-ID Regex [0-9a-f]{64} in allen Handlern (Path-Traversal-Schutz)
- SEC-26: SMTP Fail-Closed — leere AllowedIPs blockiert alles statt zu erlauben
- SEC-28: handleGetRaw — Parse-Fehler bricht ab statt Fallthrough zu Dateizugriff

BREAKING: IMAP/POP3/LDAP-Passwörter müssen nach Deploy einmalig neu eingegeben
werden (neuer AES-Key). JWT-Sessions laufen ab (einmaliges Re-Login nötig).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/archivmail/main.go

@@ -3,9 +3,11 @@ package main
 import (
 	"context"
 	"crypto/rand"
+	"crypto/sha256"
 	"encoding/hex"
 	"flag"
 	"fmt"
+	"io"
 	"log/slog"
 	"net/http"
 	"os"
@@ -14,6 +16,8 @@ import (
 	"syscall"
 	"time"
 
+	"golang.org/x/crypto/hkdf"
+
 	"github.com/archivmail/config"
 	"github.com/archivmail/internal/api"
 	"github.com/archivmail/internal/audit"
@@ -67,6 +71,26 @@ func main() {
 		os.Exit(1)
 	}
 
+	// SEC-08: Derive separate keys from the master secret to prevent key reuse.
+	// jwtSecret is used for JWT token signing only.
+	// aesKey is used for AES-256-GCM encryption of stored passwords (IMAP, POP3, LDAP).
+	// HKDF is deterministic: same cfg.API.Secret always produces the same derived keys.
+	// NOTE: After this change, existing stored IMAP/POP3/LDAP passwords must be
+	// re-entered once, as they were encrypted with the old undivided key.
+	masterKey := []byte(cfg.API.Secret)
+	jwtKeyRaw := make([]byte, 32)
+	if _, err := io.ReadFull(hkdf.New(sha256.New, masterKey, []byte("archivmail-jwt-v1"), nil), jwtKeyRaw); err != nil {
+		logger.Error("key derivation failed", "err", err)
+		os.Exit(1)
+	}
+	aesKeyRaw := make([]byte, 32)
+	if _, err := io.ReadFull(hkdf.New(sha256.New, masterKey, []byte("archivmail-aes-v1"), nil), aesKeyRaw); err != nil {
+		logger.Error("key derivation failed", "err", err)
+		os.Exit(1)
+	}
+	jwtSecret := hex.EncodeToString(jwtKeyRaw)
+	aesKey := hex.EncodeToString(aesKeyRaw)
+
 	// Storage with encryption + DB metadata
 	storeCfg := storage.Config{
 		Dir:     cfg.Storage.StorePath,
@@ -127,7 +151,7 @@ func main() {
 	}
 
 	// LDAP config store
-	ldapSt, err := ldapcfg.New(cfg.Database.DSN(), cfg.API.Secret)
+	ldapSt, err := ldapcfg.New(cfg.Database.DSN(), aesKey)
 	if err != nil {
 		logger.Error("ldap config store init failed", "err", err)
 		os.Exit(1)
@@ -135,12 +159,12 @@ func main() {
 	defer ldapSt.Close()
 
 	// Auth manager (with LDAP fallback)
-	authMgr := auth.New(users, ldapSt, cfg.API.Secret)
+	authMgr := auth.New(users, ldapSt, jwtSecret)
 
 	// API server
 	apiCfg := config.APIConfig{
 		Bind:   cfg.API.Bind,
-		Secret: cfg.API.Secret,
+		Secret: jwtSecret,
 	}
 	srv := api.New(apiCfg, mailStore, idx, authMgr, users, audlog, logger)
 
@@ -200,7 +224,7 @@ func main() {
 	srv.SetSMTPDaemon(smtpDaemon)
 
 	// IMAP store + importer + scheduler (wired to use async worker)
-	imapSt, err := imapstore.New(cfg.Database.DSN(), cfg.API.Secret)
+	imapSt, err := imapstore.New(cfg.Database.DSN(), aesKey)
 	if err != nil {
 		logger.Error("imap store init failed", "err", err)
 		os.Exit(1)
@@ -213,7 +237,7 @@ func main() {
 	srv.SetImap(imapSt, imapImp, imapSched)
 
 	// POP3 store + importer
-	pop3St, err := pop3store.New(cfg.Database.DSN(), cfg.API.Secret)
+	pop3St, err := pop3store.New(cfg.Database.DSN(), aesKey)
 	if err != nil {
 		logger.Error("pop3 store init failed", "err", err)
 		os.Exit(1)

config/config.go

@@ -56,6 +56,9 @@ func (d DatabaseConfig) DSN() string {
 }
 
 // SMTPConfig holds settings for the embedded SMTP server.
+// SEC-26: AllowedIPs uses fail-closed logic. An empty list means NO IP is
+// allowed to connect. To accept from any IP, explicitly set:
+//   allowed_ips: ["0.0.0.0/0", "::/0"]
 type SMTPConfig struct {
 	Enabled         bool     `yaml:"enabled"`
 	Bind            string   `yaml:"bind"`

features/INDEX.md

@@ -35,7 +35,8 @@
 | PROJ-20 | Nutzer-Löschung & E-Mail-Verbleib (GoBD-konform) | Deployed | [PROJ-20](PROJ-20-nutzer-loeschung.md) | 2026-03-17 |
 | PROJ-21 | Multi-Mandanten-Fähigkeit (Multi-Tenancy) | In Progress | [PROJ-21](PROJ-21-multi-tenancy.md) | 2026-03-17 |
 | PROJ-22 | LDAP / AD – Web-GUI Konfiguration & Test | Deployed | [PROJ-22](PROJ-22-ldap-webgui.md) | 2026-03-17 |
+| PROJ-23 | Pro-Mandant LDAP / Active Directory (Multi-Tenant Phase B) | Planned | [PROJ-23](PROJ-23-tenant-ldap-pro-mandant.md) | 2026-03-17 |
 
 <!-- Add features above this line -->
 
-## Next Available ID: PROJ-23
+## Next Available ID: PROJ-24

internal/api/export.go

@@ -327,6 +327,11 @@ func buildMailPDF(id string, pm *mailparser.ParsedMail, rawSize int) []byte {
 
 func (s *Server) handleExportPDF(w http.ResponseWriter, r *http.Request) {
 	id := r.PathValue("id")
+	// SEC-22: Validate mail ID format to prevent path traversal.
+	if !isValidMailID(id) {
+		writeError(w, http.StatusBadRequest, "invalid mail id")
+		return
+	}
 
 	raw, err := s.store.Load(id)
 	if err != nil {
@@ -340,8 +345,18 @@ func (s *Server) handleExportPDF(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// User role: only own mailbox
 	sess := sessionFromCtx(r.Context())
+
+	// SEC-05: Tenant isolation for PDF export.
+	if sess.TenantID != nil {
+		mailTenant, _ := s.store.GetTenantForMail(r.Context(), id)
+		if mailTenant == nil || *mailTenant != *sess.TenantID {
+			writeError(w, http.StatusForbidden, "access denied")
+			return
+		}
+	}
+
+	// User role: only own mailbox
 	if sess.Role == userstore.RoleUser {
 		u, err := s.users.GetByUsername(sess.Username)
 		if err != nil || !mailBelongsToUser(pm, u.Email) {
@@ -394,8 +409,35 @@ func (s *Server) handleExportZIP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// SEC-22: Validate all mail IDs before processing.
+	for _, id := range req.IDs {
+		if !isValidMailID(id) {
+			writeError(w, http.StatusBadRequest, "invalid mail id")
+			return
+		}
+	}
+
 	sess := sessionFromCtx(r.Context())
 
+	// SEC-05: Tenant isolation — verify all requested IDs belong to caller's tenant.
+	if sess.TenantID != nil {
+		allowedIDs, err := s.store.GetAllIDsByTenant(r.Context(), sess.TenantID)
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "tenant check failed")
+			return
+		}
+		allowed := make(map[string]struct{}, len(allowedIDs))
+		for _, aid := range allowedIDs {
+			allowed[aid] = struct{}{}
+		}
+		for _, id := range req.IDs {
+			if _, ok := allowed[id]; !ok {
+				writeError(w, http.StatusForbidden, "access denied")
+				return
+			}
+		}
+	}
+
 	// For RoleUser, look up user email once for access checks
 	var userEmail string
 	if sess.Role == userstore.RoleUser {

internal/api/server.go

@@ -17,6 +17,8 @@ import (
 	"syscall"
 	"time"
 
+	"regexp"
+
 	"github.com/archivmail/config"
 	"github.com/archivmail/internal/audit"
 	"github.com/archivmail/internal/auth"
@@ -31,6 +33,27 @@ import (
 	"github.com/archivmail/pkg/mailparser"
 )
 
+// SEC-22: Compiled regex for mail ID validation to prevent path traversal.
+var mailIDRegex = regexp.MustCompile(`^[0-9a-f]{64}$`)
+
+// isValidMailID validates that a mail ID matches the expected hex format.
+func isValidMailID(id string) bool {
+	return mailIDRegex.MatchString(id)
+}
+
+// roleLevel returns the privilege level for a role string.
+// Hierarchy: superadmin=5 > admin=4 > domain_admin=3 > auditor=2 > user=1
+func roleLevel(role string) int {
+	levels := map[string]int{
+		userstore.RoleUser:        1,
+		userstore.RoleAuditor:     2,
+		userstore.RoleDomainAdmin: 3,
+		userstore.RoleAdmin:       4,
+		userstore.RoleSuperAdmin:  5,
+	}
+	return levels[role]
+}
+
 type contextKey string
 
 const (
@@ -132,7 +155,8 @@ func (s *Server) routes() {
 
 	s.mux.HandleFunc("GET /api/admin/system/stats", s.authAdmin(s.handleSystemStats))
 	s.mux.HandleFunc("GET /api/admin/security/audit", s.authAdmin(s.handleSecurityAudit))
-	s.mux.HandleFunc("POST /api/admin/security/fix", s.authAdmin(s.handleSecurityFix))
+	// SEC-17: Security fix actions require superadmin, not just domain_admin.
+	s.mux.HandleFunc("POST /api/admin/security/fix", s.auth(s.requireRole(userstore.RoleSuperAdmin, s.handleSecurityFix)))
 
 	// Export routes
 	s.mux.HandleFunc("GET /api/export/pdf/{id}", s.auth(s.requireMailAccess(s.handleExportPDF)))
@@ -350,18 +374,33 @@ func (s *Server) handleCreateUser(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// SEC-01: Privilege escalation check — caller must not assign a role
+	// at or above their own level.
+	sess := sessionFromCtx(r.Context())
+	if roleLevel(req.Role) >= roleLevel(sess.Role) {
+		writeError(w, http.StatusForbidden, "insufficient privileges to assign this role")
+		return
+	}
+
+	// SEC-02: Tenant isolation — non-superadmin users can only create users
+	// within their own tenant.
+	var tenantID *int64
+	if sess.TenantID != nil {
+		tenantID = sess.TenantID
+	}
+
 	user, err := s.users.Create(userstore.CreateUserRequest{
 		Username: req.Username,
 		Email:    req.Email,
 		Password: req.Password,
 		Role:     req.Role,
+		TenantID: tenantID,
 	})
 	if err != nil {
 		writeError(w, http.StatusBadRequest, err.Error())
 		return
 	}
 
-	sess := sessionFromCtx(r.Context())
 	s.audlog.Log(audit.Entry{
 		EventType: audit.EventUserMgmt,
 		Username:  sess.Username,
@@ -397,6 +436,33 @@ func (s *Server) handleUpdateUser(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	sess := sessionFromCtx(r.Context())
+
+	// SEC-02: Tenant isolation — load target user and verify same tenant.
+	target, err := s.users.GetByID(id)
+	if err != nil {
+		writeError(w, http.StatusNotFound, "user not found")
+		return
+	}
+	if sess.TenantID != nil {
+		if target.TenantID == nil || *target.TenantID != *sess.TenantID {
+			writeError(w, http.StatusForbidden, "access denied")
+			return
+		}
+	}
+
+	// SEC-01: Privilege escalation check — caller must not assign a role
+	// at or above their own level, and must not modify users at or above
+	// their own level.
+	if roleLevel(target.Role) >= roleLevel(sess.Role) {
+		writeError(w, http.StatusForbidden, "insufficient privileges to modify this user")
+		return
+	}
+	if req.Role != nil && roleLevel(*req.Role) >= roleLevel(sess.Role) {
+		writeError(w, http.StatusForbidden, "insufficient privileges to assign this role")
+		return
+	}
+
 	updated, err := s.users.Update(id, userstore.UpdateUserRequest{
 		Email:    req.Email,
 		Role:     req.Role,
@@ -408,7 +474,6 @@ func (s *Server) handleUpdateUser(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	sess := sessionFromCtx(r.Context())
 	s.audlog.Log(audit.Entry{
 		EventType: audit.EventUserMgmt,
 		Username:  sess.Username,
@@ -440,6 +505,21 @@ func (s *Server) handleDeleteUser(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	// SEC-02: Tenant isolation — domain_admin can only delete users in their own tenant.
+	sess := sessionFromCtx(r.Context())
+	if sess.TenantID != nil {
+		if target.TenantID == nil || *target.TenantID != *sess.TenantID {
+			writeError(w, http.StatusForbidden, "access denied")
+			return
+		}
+	}
+
+	// SEC-01: Cannot delete users at or above own privilege level.
+	if roleLevel(target.Role) >= roleLevel(sess.Role) {
+		writeError(w, http.StatusForbidden, "insufficient privileges to delete this user")
+		return
+	}
+
 	if err := s.users.DeleteSafe(id); err != nil {
 		if err.Error() == "userstore: cannot delete last admin" {
 			writeError(w, http.StatusConflict, "cannot delete the last active admin")
@@ -459,7 +539,6 @@ func (s *Server) handleDeleteUser(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	sess := sessionFromCtx(r.Context())
 	s.audlog.Log(audit.Entry{
 		EventType: audit.EventUserMgmt,
 		Username:  sess.Username,
@@ -808,6 +887,11 @@ func (s *Server) requireMailAccess(next http.HandlerFunc) http.HandlerFunc {
 
 func (s *Server) handleGetMail(w http.ResponseWriter, r *http.Request) {
 	id := r.PathValue("id")
+	// SEC-22: Validate mail ID format to prevent path traversal.
+	if !isValidMailID(id) {
+		writeError(w, http.StatusBadRequest, "invalid mail id")
+		return
+	}
 
 	raw, err := s.store.Load(id)
 	if err != nil {
@@ -892,6 +976,11 @@ func (s *Server) handleGetMail(w http.ResponseWriter, r *http.Request) {
 
 func (s *Server) handleGetAttachment(w http.ResponseWriter, r *http.Request) {
 	id := r.PathValue("id")
+	// SEC-22: Validate mail ID format to prevent path traversal.
+	if !isValidMailID(id) {
+		writeError(w, http.StatusBadRequest, "invalid mail id")
+		return
+	}
 	indexStr := r.PathValue("index")
 	idx, err := strconv.Atoi(indexStr)
 	if err != nil {
@@ -950,6 +1039,11 @@ func (s *Server) handleGetAttachment(w http.ResponseWriter, r *http.Request) {
 
 func (s *Server) handleGetRaw(w http.ResponseWriter, r *http.Request) {
 	id := r.PathValue("id")
+	// SEC-22: Validate mail ID format to prevent path traversal.
+	if !isValidMailID(id) {
+		writeError(w, http.StatusBadRequest, "invalid mail id")
+		return
+	}
 
 	raw, err := s.store.Load(id)
 	if err != nil {
@@ -968,17 +1062,19 @@ func (s *Server) handleGetRaw(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	// Access check for user role
+	// SEC-28: Access check for user role — parse failure must NOT grant access.
 	if sess.Role == userstore.RoleUser {
 		pm, err := mailparser.Parse(raw)
-		if err == nil {
+		if err != nil {
+			writeError(w, http.StatusInternalServerError, "failed to parse mail")
+			return
+		}
 		u, err := s.users.GetByUsername(sess.Username)
 		if err != nil || !mailBelongsToUser(pm, u.Email) {
 			writeError(w, http.StatusForbidden, "access denied")
 			return
 		}
 	}
-	}
 
 	w.Header().Set("Content-Type", "message/rfc822")
 	w.Header().Set("Content-Disposition", fmt.Sprintf(`attachment; filename="%s.eml"`, id[:16]))
@@ -1182,7 +1278,8 @@ func (s *Server) handleListImap(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	sess := sessionFromCtx(r.Context())
-	isAdmin := sess.Role == userstore.RoleAdmin
+	// SEC-03: Use HasRole to correctly check admin privileges (domain_admin, admin, superadmin).
+	isAdmin := auth.HasRole(sess.Role, userstore.RoleDomainAdmin)
 	accounts, err := s.imapStore.List(r.Context(), sess.Username, isAdmin)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "failed to list IMAP accounts")
@@ -1265,7 +1362,7 @@ func (s *Server) handleDeleteImap(w http.ResponseWriter, r *http.Request) {
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}
@@ -1353,7 +1450,7 @@ func (s *Server) handleStartImport(w http.ResponseWriter, r *http.Request) {
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}
@@ -1389,7 +1486,7 @@ func (s *Server) handleImapProgress(w http.ResponseWriter, r *http.Request) {
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}
@@ -1417,7 +1514,7 @@ func (s *Server) handleSyncNow(w http.ResponseWriter, r *http.Request) {
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}
@@ -1452,7 +1549,7 @@ func (s *Server) handleUpdateImapInterval(w http.ResponseWriter, r *http.Request
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}
@@ -1860,7 +1957,8 @@ func (s *Server) handleListPop3(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	sess := sessionFromCtx(r.Context())
-	isAdmin := sess.Role == userstore.RoleAdmin
+	// SEC-03: Use HasRole to correctly check admin privileges (domain_admin, admin, superadmin).
+	isAdmin := auth.HasRole(sess.Role, userstore.RoleDomainAdmin)
 	accounts, err := s.pop3Store.List(r.Context(), sess.Username, isAdmin)
 	if err != nil {
 		writeError(w, http.StatusInternalServerError, "failed to list POP3 accounts")
@@ -1940,7 +2038,7 @@ func (s *Server) handleDeletePop3(w http.ResponseWriter, r *http.Request) {
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}
@@ -2032,7 +2130,7 @@ func (s *Server) handleStartPop3Import(w http.ResponseWriter, r *http.Request) {
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}
@@ -2068,7 +2166,7 @@ func (s *Server) handlePop3Progress(w http.ResponseWriter, r *http.Request) {
 	}
 
 	sess := sessionFromCtx(r.Context())
-	if acc.Owner != sess.Username && sess.Role != userstore.RoleAdmin {
+	if acc.Owner != sess.Username && !auth.HasRole(sess.Role, userstore.RoleDomainAdmin) {
 		writeError(w, http.StatusForbidden, "access denied")
 		return
 	}

internal/smtpd/smtpd.go

@@ -310,11 +310,12 @@ func (s *session) Logout() error {
 
 // ── Helpers ───────────────────────────────────────────────────────────────
 
-// isAllowed returns true if the IP is in the allowlist, or if the allowlist
+// isAllowed returns true if the IP is in the allowlist.
-// is empty (allow-all mode for development).
+// SEC-26: Fail-closed — empty allowlist means NO IP is allowed (was fail-open before).
+// To allow all IPs, set allowed_ips: ["0.0.0.0/0", "::/0"] explicitly in config.
 func (d *Daemon) isAllowed(ip string) bool {
 	if len(d.cfg.AllowedIPs) == 0 {
-		return true // no restriction configured
+		return false // fail-closed: no IPs configured = block everything
 	}
 	for _, allowed := range d.cfg.AllowedIPs {
 		// Support CIDR notation (e.g. 192.168.1.0/24)