diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7b3e92c..5208b22 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,26 @@
 ## Changelog
 
+### v0.76.0 — campaign-#3 hardening: settings recovery, restore-name validation, quiesce-marker quarantine (2026-06-22)
+
+Three controller findings from chaos campaign #3, all small, all controller-side.
+
+- **S1 [MEDIUM] — no more crash-loop on a corrupt `settings.json`.** `internal/settings/settings.go`:
+  `save()` now writes a last-known-good `<path>.bak` **after** the primary rename succeeds (best-effort);
+  `Load()` on a JSON-parse error recovers from `.bak` (re-promotes it to primary) and, failing that,
+  **preserves** the corrupt file as `*.corrupt-<ts>` and starts on safe defaults — never returns the
+  error that made `main.go` `Fatalf`/crash-loop. New `Settings.LoadWarning` surfaced as a dashboard
+  banner. (`main.go`'s `Fatalf` stays — now only the genuine IO-unreadable path is fatal.) Recovery is
+  safe: an empty `PasswordHash` falls back to `controller.yaml`, the storage registry re-discovers.
+- **F2 [MEDIUM, defense-in-depth] — validate `stack_name` against path traversal.** New
+  `web/validate.go` `validStackName` (single segment; rejects `/`, `\`, `..`, NUL). Gated in
+  `backupRestoreHandler` (`handlers.go`) and `apiExportStart` (`handler_export.go`) before any
+  restore/export work. (Storage `where=` was already validated by `gateWhere`.)
+- **S3 [LOW] — quarantine a corrupt quiesce marker.** `quiesce/quiesce.go` `readMarker` now logs a
+  `[WARN]` + renames a bad-JSON marker to `*.corrupt-<ts>` instead of silently dropping it (still
+  returns "no marker" → no recovery, the correct contract).
+- Tests: T-S1a-d (settings recovery), T-F2a-c (validation + both handlers), T-S3a/b (quarantine), all
+  red-proofed against the pre-fix code. Agent/hub untouched.
+
 ### v0.75.0 — gate userdata MkdirAll on a live mountpoint (no writes into an absent drive) (2026-06-22)
 
 **Bugfix — two `MkdirAll`-into-`<drive>/userdata` sites fired without checking the drive was mounted**,
diff --git a/controller/internal/quiesce/quiesce.go b/controller/internal/quiesce/quiesce.go
index 6eab642..92440f1 100644
--- a/controller/internal/quiesce/quiesce.go
+++ b/controller/internal/quiesce/quiesce.go
@@ -319,7 +319,12 @@ func (l *Loop) readMarker() (Marker, bool) {
 		return Marker{}, false
 	}
 	var m Marker
-	if json.Unmarshal(data, &m) != nil {
+	if err := json.Unmarshal(data, &m); err != nil {
+		// S3: a corrupt marker is NOT silently dropped — log it LOUD and quarantine the bad file (a real
+		// corrupted-mid-quiesce marker would otherwise skip stack-recovery with no trace). Still return
+		// false: "no usable marker" ⇒ no recovery is the correct contract.
+		l.logger.Printf("[WARN] [quiesce] marker at %s is corrupt (%v) — quarantining; stacks not auto-recovered from it", l.markerPath, err)
+		_ = os.Rename(l.markerPath, fmt.Sprintf("%s.corrupt-%d", l.markerPath, l.now().Unix()))
 		return Marker{}, false
 	}
 	return m, true
diff --git a/controller/internal/quiesce/quiesce_marker_test.go b/controller/internal/quiesce/quiesce_marker_test.go
new file mode 100644
index 0000000..dec671a
--- /dev/null
+++ b/controller/internal/quiesce/quiesce_marker_test.go
@@ -0,0 +1,56 @@
+package quiesce
+
+import (
+	"bytes"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+	"time"
+)
+
+// T-S3a: a corrupt marker is quarantined + logged (not silently dropped). Still returns false.
+// Companion: pre-fix readMarker (silent return false) → no *.corrupt-* + no log → this fails.
+func TestReadMarker_QuarantinesCorrupt(t *testing.T) {
+	mp := filepath.Join(t.TempDir(), "quiesce-state.json")
+	if err := os.WriteFile(mp, []byte(`{ "active": true, BROKEN not json`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	var buf bytes.Buffer
+	l := New(Options{
+		MarkerPath: mp, Poll: time.Hour, StatusPoll: time.Millisecond, MaxQuiesce: time.Second,
+		Logger: log.New(&buf, "", 0),
+	})
+	if _, ok := l.readMarker(); ok {
+		t.Fatal("corrupt marker must return ok=false")
+	}
+	if m, _ := filepath.Glob(mp + ".corrupt-*"); len(m) == 0 {
+		t.Error("corrupt marker must be quarantined as *.corrupt-*")
+	}
+	if !strings.Contains(buf.String(), "corrupt") {
+		t.Errorf("expected a WARN about the corrupt marker, got: %q", buf.String())
+	}
+}
+
+// T-S3b: valid marker → (marker, true), no quarantine (regression).
+func TestReadMarker_HappyPath(t *testing.T) {
+	mp := filepath.Join(t.TempDir(), "quiesce-state.json")
+	if err := os.WriteFile(mp, []byte(`{"active":true,"stopped_stacks":["romm","komga"]}`), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	l := New(Options{
+		MarkerPath: mp, Poll: time.Hour, StatusPoll: time.Millisecond, MaxQuiesce: time.Second,
+		Logger: log.New(&bytes.Buffer{}, "", 0),
+	})
+	m, ok := l.readMarker()
+	if !ok {
+		t.Fatal("valid marker must return ok=true")
+	}
+	if len(m.StoppedStacks) != 2 {
+		t.Errorf("expected 2 stopped stacks, got %d", len(m.StoppedStacks))
+	}
+	if g, _ := filepath.Glob(mp + ".corrupt-*"); len(g) != 0 {
+		t.Error("happy path must NOT quarantine")
+	}
+}
diff --git a/controller/internal/settings/settings.go b/controller/internal/settings/settings.go
index 81b0675..37ffd47 100644
--- a/controller/internal/settings/settings.go
+++ b/controller/internal/settings/settings.go
@@ -21,6 +21,10 @@ type Settings struct {
 	log   *log.Logger  `json:"-"`
 	debug bool         `json:"-"`
 
+	// LoadWarning is set (non-empty, Hungarian) when Load recovered from a corrupt settings.json —
+	// surfaced to the dashboard as a persistent banner. Not persisted.
+	LoadWarning string `json:"-"`
+
 	// Auth
 	PasswordHash string `json:"password_hash,omitempty"` // bcrypt hash, overrides controller.yaml
 
@@ -198,7 +202,24 @@ func Load(path string, logger *log.Logger) (*Settings, error) {
 	}
 
 	if err := json.Unmarshal(data, s); err != nil {
-		return nil, fmt.Errorf("parsing settings file: %w", err)
+		// CORRUPT primary — never crash-loop. Recover from the last-known-good .bak; failing that,
+		// preserve the corrupt file for forensics and start on safe defaults (recoverable: an empty
+		// PasswordHash falls back to controller.yaml; the storage registry re-discovers on startup).
+		logger.Printf("[ERROR] [settings] primary settings corrupt (%v) — attempting recovery from .bak", err)
+		if bak, berr := os.ReadFile(path + ".bak"); berr == nil {
+			s2 := &Settings{path: path, log: logger}
+			if json.Unmarshal(bak, s2) == nil {
+				logger.Printf("[WARN] [settings] recovered settings from .bak; re-promoting to primary")
+				_ = os.WriteFile(path, bak, 0644) // best-effort promote
+				s2.LoadWarning = "settings.json volt sérült — visszaállítva biztonsági másolatból"
+				s2.migrateResticToRsync()
+				return s2, nil
+			}
+		}
+		corrupt := fmt.Sprintf("%s.corrupt-%d", path, time.Now().Unix())
+		_ = os.Rename(path, corrupt)
+		logger.Printf("[ERROR] [settings] settings unrecoverable — preserved as %s; starting with safe defaults", corrupt)
+		return &Settings{path: path, log: logger, LoadWarning: "settings.json sérült és helyreállíthatatlan — alapértelmezett beállítások"}, nil
 	}
 
 	logger.Printf("[INFO] [settings] Loaded settings from %s", path)
@@ -266,6 +287,12 @@ func (s *Settings) save() error {
 		return fmt.Errorf("renaming settings file: %w", err)
 	}
 
+	// last-known-good: written AFTER the primary rename succeeds, so .bak only ever holds settings that
+	// parsed + saved cleanly. Best-effort — a failed .bak must NOT fail the save.
+	if err := os.WriteFile(s.path+".bak", data, 0644); err != nil && s.log != nil {
+		s.log.Printf("[WARN] [settings] could not write .bak: %v", err)
+	}
+
 	if s.debug {
 		s.log.Printf("[DEBUG] [settings] saved to %s (%d bytes)", s.path, len(data))
 	}
diff --git a/controller/internal/settings/settings_recovery_test.go b/controller/internal/settings/settings_recovery_test.go
new file mode 100644
index 0000000..c3478b7
--- /dev/null
+++ b/controller/internal/settings/settings_recovery_test.go
@@ -0,0 +1,93 @@
+package settings
+
+import (
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+func discardLog() *log.Logger { return log.New(io.Discard, "", 0) }
+
+// T-S1a: a corrupt primary recovers from the last-known-good .bak (no error, no crash-loop).
+// Companion: pre-fix Load (return error on parse) → err != nil → this fails.
+func TestLoad_RecoversFromBak(t *testing.T) {
+	p := filepath.Join(t.TempDir(), "settings.json")
+	if err := os.WriteFile(p+".bak", []byte(`{"password_hash":"bak-hash"}`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(p, []byte(`{"password_hash": BROKEN not json`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	s, err := Load(p, discardLog())
+	if err != nil {
+		t.Fatalf("Load must not error (no crash-loop): %v", err)
+	}
+	if s.GetPasswordHash() != "bak-hash" {
+		t.Fatalf("want recovered hash bak-hash, got %q", s.GetPasswordHash())
+	}
+	if s.LoadWarning == "" {
+		t.Error("expected LoadWarning to be set after recovery")
+	}
+	if b, _ := os.ReadFile(p); !strings.Contains(string(b), "bak-hash") {
+		t.Error("primary should be re-promoted from .bak")
+	}
+}
+
+// T-S1b: unrecoverable (corrupt primary, no .bak) → safe defaults, NO error, corrupt file preserved.
+func TestLoad_UnrecoverableNoBak(t *testing.T) {
+	p := filepath.Join(t.TempDir(), "settings.json")
+	if err := os.WriteFile(p, []byte(`{ BROKEN not json`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	s, err := Load(p, discardLog())
+	if err != nil {
+		t.Fatalf("Load must not error (no crash-loop): %v", err)
+	}
+	if s == nil {
+		t.Fatal("expected non-nil safe-default settings")
+	}
+	if s.LoadWarning == "" {
+		t.Error("expected LoadWarning to be set")
+	}
+	if m, _ := filepath.Glob(p + ".corrupt-*"); len(m) == 0 {
+		t.Error("corrupt file must be preserved as *.corrupt-*")
+	}
+	if _, e := os.Stat(p); e == nil {
+		t.Error("original corrupt primary should have been renamed away")
+	}
+}
+
+// T-S1c: save() writes a .bak equal to the primary (last-known-good).
+func TestSave_WritesBak(t *testing.T) {
+	p := filepath.Join(t.TempDir(), "settings.json")
+	s, err := Load(p, discardLog()) // no file → defaults
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := s.SetPasswordHash("h1"); err != nil { // SetPasswordHash persists via save()
+		t.Fatal(err)
+	}
+	prim, _ := os.ReadFile(p)
+	bak, e := os.ReadFile(p + ".bak")
+	if e != nil {
+		t.Fatalf(".bak missing after save: %v", e)
+	}
+	if string(prim) != string(bak) {
+		t.Error(".bak must equal the primary after save")
+	}
+}
+
+// T-S1d: happy path — valid primary loads normally, no warning (regression).
+func TestLoad_HappyPath(t *testing.T) {
+	p := filepath.Join(t.TempDir(), "settings.json")
+	if err := os.WriteFile(p, []byte(`{"password_hash":"good"}`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	s, err := Load(p, discardLog())
+	if err != nil || s.GetPasswordHash() != "good" || s.LoadWarning != "" {
+		t.Fatalf("happy load failed: err=%v hash=%q warn=%q", err, s.GetPasswordHash(), s.LoadWarning)
+	}
+}
diff --git a/controller/internal/web/handler_export.go b/controller/internal/web/handler_export.go
index b1d8869..5928584 100644
--- a/controller/internal/web/handler_export.go
+++ b/controller/internal/web/handler_export.go
@@ -166,6 +166,11 @@ func (s *Server) apiExportStart(w http.ResponseWriter, r *http.Request) {
 		jsonError(w, "Missing stack_name or dest_drive", http.StatusBadRequest)
 		return
 	}
+	// F2 (defense-in-depth): reject a traversal/escape stack_name before any export work.
+	if !validStackName(req.StackName) {
+		jsonError(w, "Invalid stack_name", http.StatusBadRequest)
+		return
+	}
 
 	if !s.isValidDrivePath(req.DestDrive) {
 		s.logger.Printf("[DEBUG] [web] apiExportStart: invalid drive path %q", req.DestDrive)
diff --git a/controller/internal/web/handlers.go b/controller/internal/web/handlers.go
index 192f50a..c857113 100644
--- a/controller/internal/web/handlers.go
+++ b/controller/internal/web/handlers.go
@@ -151,6 +151,7 @@ func (s *Server) dashboardHandler(w http.ResponseWriter, r *http.Request) {
 	sysInfo := system.GetInfo(s.primaryHDDPath(), s.cpuCollector)
 
 	data := s.baseData("dashboard", "Vezérlőpult")
+	data["SettingsWarning"] = s.settings.LoadWarning // non-empty if settings.json was recovered from corruption
 	data["Stacks"] = deployedStacks
 	data["MissingStorage"] = s.missingStorageMap(deployedStacks)
 	data["RunningCount"] = running
@@ -795,6 +796,13 @@ func (s *Server) backupRestoreHandler(w http.ResponseWriter, r *http.Request) {
 		http.Redirect(w, r, "/backups?flash_error=Hi%C3%A1nyz%C3%B3+param%C3%A9terek", http.StatusFound)
 		return
 	}
+	// F2 (defense-in-depth): a stack name is a single segment, never a path. Reject traversal before any
+	// restore work — never let it reach RestoreFromRecoveryUnit.
+	if !validStackName(stackName) {
+		s.logger.Printf("[WARN] [web] restore rejected: invalid stack_name %q from %s", stackName, r.RemoteAddr)
+		http.Redirect(w, r, "/backups?flash_error=%C3%89rv%C3%A9nytelen+alkalmaz%C3%A1sn%C3%A9v", http.StatusFound)
+		return
+	}
 
 	if s.backupMgr == nil {
 		http.Redirect(w, r, "/backups?flash_error=Ment%C3%A9s+nincs+be%C3%A1ll%C3%ADtva", http.StatusFound)
diff --git a/controller/internal/web/templates/dashboard.html b/controller/internal/web/templates/dashboard.html
index e6b45c3..7a87afb 100644
--- a/controller/internal/web/templates/dashboard.html
+++ b/controller/internal/web/templates/dashboard.html
@@ -87,6 +87,14 @@
         {{end}}
         {{end}}
     </div>
+    {{if .SettingsWarning}}
+    <div class="inline-warnings">
+        <div class="inline-warning inline-warning-error">
+            <span class="inline-warning-dot">●</span>
+            <span class="inline-warning-text">{{.SettingsWarning}}</span>
+        </div>
+    </div>
+    {{end}}
     {{if .DiskWarnings}}
     <div class="inline-warnings">
         {{range .DiskWarnings}}
diff --git a/controller/internal/web/validate.go b/controller/internal/web/validate.go
new file mode 100644
index 0000000..88feeec
--- /dev/null
+++ b/controller/internal/web/validate.go
@@ -0,0 +1,19 @@
+package web
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// validStackName reports whether name is a safe stack identifier: a single path segment, never a path.
+// Rejects traversal/escape (`..`, `/`, `\`, NUL) so a stack_name can never be turned into a filesystem
+// path that escapes the stacks/userdata tree. (Storage `where=` is validated separately by gateWhere.)
+func validStackName(name string) bool {
+	if name == "" || name == "." || name == ".." {
+		return false
+	}
+	if strings.ContainsAny(name, "/\\\x00") {
+		return false
+	}
+	return name == filepath.Clean(name)
+}
diff --git a/controller/internal/web/validate_test.go b/controller/internal/web/validate_test.go
new file mode 100644
index 0000000..9af8a92
--- /dev/null
+++ b/controller/internal/web/validate_test.go
@@ -0,0 +1,61 @@
+package web
+
+import (
+	"io"
+	"log"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"gitea.dooplex.hu/admin/felhom-controller/internal/appexport"
+	"gitea.dooplex.hu/admin/felhom-controller/internal/config"
+)
+
+// T-F2a: validStackName rejects traversal/escape, accepts real single-segment names. (pure)
+func TestValidStackName(t *testing.T) {
+	for _, bad := range []string{"../../etc", "a/b", "..", ".", "", "a\x00b", "a\\b", "../x", "/etc"} {
+		if validStackName(bad) {
+			t.Errorf("validStackName(%q) = true, want false", bad)
+		}
+	}
+	for _, good := range []string{"paperless-ngx", "immich", "romm", "uptime-kuma"} {
+		if !validStackName(good) {
+			t.Errorf("validStackName(%q) = false, want true", good)
+		}
+	}
+}
+
+// T-F2b: the restore handler rejects a traversal stack_name with the flash-error redirect and never
+// reaches RestoreFromRecoveryUnit (backupMgr is nil — if the gate failed to fire, it would nil-panic
+// or fall through to the "Mentés nincs beállítva" path, not the "Érvénytelen" one).
+// Companion: drop the gate → traversal falls through to the nil-backupMgr path → different redirect → fails.
+func TestBackupRestoreHandler_RejectsTraversal(t *testing.T) {
+	s := &Server{cfg: &config.Config{}, logger: log.New(io.Discard, "", 0)} // backupMgr == nil
+	form := "stack_name=../../../etc&snapshot_id=x"
+	req := httptest.NewRequest("POST", "/backup/restore", strings.NewReader(form))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	rec := httptest.NewRecorder()
+
+	s.backupRestoreHandler(rec, req) // must not panic
+
+	loc := rec.Header().Get("Location")
+	if !strings.Contains(loc, "rv%C3%A9nytelen") { // "Érvénytelen" (invalid name) — the gate's redirect
+		t.Fatalf("expected traversal rejection redirect, got Location=%q", loc)
+	}
+}
+
+// T-F2c: the export handler rejects a traversal stack_name with 400 (before any export work).
+func TestExportStart_RejectsTraversal(t *testing.T) {
+	// non-nil exporter so we pass the "not available" guard and reach the stack_name gate (the gate
+	// returns before the exporter is ever used).
+	s := &Server{cfg: &config.Config{}, logger: log.New(io.Discard, "", 0), appExporter: &appexport.Exporter{}}
+	body := `{"stack_name":"../../etc","dest_drive":"/mnt/x"}`
+	req := httptest.NewRequest("POST", "/api/export/start", strings.NewReader(body))
+	rec := httptest.NewRecorder()
+
+	s.apiExportStart(rec, req) // must not panic
+
+	if rec.Code != 400 {
+		t.Fatalf("expected 400 for traversal stack_name, got %d", rec.Code)
+	}
+}