diff --git a/apps/openant-cli/internal/config/config.go b/apps/openant-cli/internal/config/config.go
index 0af8f521..9171994c 100644
--- a/apps/openant-cli/internal/config/config.go
+++ b/apps/openant-cli/internal/config/config.go
@@ -107,6 +107,12 @@ func Save(cfg *Config) error {
 		return fmt.Errorf("failed to write config: %w", err)
 	}
 
+	// os.WriteFile only applies the mode when it CREATES the file; a pre-existing config
+	// may hold an API key under looser permissions, so enforce 0600 explicitly (CWE-732).
+	if err := os.Chmod(path, 0600); err != nil {
+		return fmt.Errorf("failed to restrict config permissions: %w", err)
+	}
+
 	return nil
 }
 
diff --git a/apps/openant-cli/internal/config/config_perms_test.go b/apps/openant-cli/internal/config/config_perms_test.go
new file mode 100644
index 00000000..f2bafa50
--- /dev/null
+++ b/apps/openant-cli/internal/config/config_perms_test.go
@@ -0,0 +1,46 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+// CWE-732: Save() does not enforce restrictive
+// permissions on a PRE-EXISTING config file. os.WriteFile only applies the mode argument
+// when it creates the file; if the config (which may hold an API key) already exists with
+// looser perms (e.g. 0644), the secret stays world-readable after Save().
+func TestSaveEnforcesRestrictivePermsOnPreexistingFile(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("POSIX file-mode bits not enforced on Windows")
+	}
+	tmp := t.TempDir()
+	t.Setenv("XDG_CONFIG_HOME", tmp)
+
+	dir := filepath.Join(tmp, "openant")
+	if err := os.MkdirAll(dir, 0700); err != nil {
+		t.Fatal(err)
+	}
+	path := filepath.Join(dir, "config.json")
+
+	// Pre-existing config file with loose (world/group-readable) permissions.
+	if err := os.WriteFile(path, []byte(`{"api_key":"old"}`), 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Chmod(path, 0644); err != nil { // defeat umask so the file is genuinely 0644
+		t.Fatal(err)
+	}
+
+	if err := Save(&Config{APIKey: "sk-secret-value"}); err != nil {
+		t.Fatalf("Save failed: %v", err)
+	}
+
+	info, err := os.Stat(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if perm := info.Mode().Perm(); perm != 0600 {
+		t.Fatalf("secret config perms = %#o, want 0600 (CWE-732: pre-existing loose perms not enforced)", perm)
+	}
+}