--- a/src/libsystemd/sd-bus/bus-internal.c
+++ b/src/libsystemd/sd-bus/bus-internal.c
@@ -45,7 +45,7 @@
         if (slash)
                 return false;

-        return true;
+        return (q - p) <= BUS_PATH_SIZE_MAX;
 }

 char* object_path_startswith(const char *a, const char *b) {
--- a/src/libsystemd/sd-bus/bus-internal.h
+++ b/src/libsystemd/sd-bus/bus-internal.h
@@ -333,6 +333,10 @@

 #define BUS_MESSAGE_SIZE_MAX (128*1024*1024)
 #define BUS_AUTH_SIZE_MAX (64*1024)
+/* Note that the D-Bus specification states that bus paths shall have no size limit. We enforce here one
+ * anyway, since truly unbounded strings are a security problem. The limit we pick is relatively large however,
+ * to not clash unnecessarily with real-life applications. */
+#define BUS_PATH_SIZE_MAX (64*1024)

 #define BUS_CONTAINER_DEPTH 128

--- a/src/libsystemd/sd-bus/bus-objects.c
+++ b/src/libsystemd/sd-bus/bus-objects.c
@@ -1134,7 +1134,8 @@
                 const char *path,
                 sd_bus_error *error) {

-        char *prefix;
+        _cleanup_free_ char *prefix = NULL;
+        size_t pl;
         int r;

         assert(bus);
@@ -1150,7 +1151,12 @@
                 return 0;

         /* Second, add fallback vtables registered for any of the prefixes */
-        prefix = alloca(strlen(path) + 1);
+        pl = strlen(path);
+        assert(pl <= BUS_PATH_SIZE_MAX);
+        prefix = new(char, pl + 1);
+        if (!prefix)
+                return -ENOMEM;
+
         OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
                 r = object_manager_serialize_path(bus, reply, prefix, path, true, error);
                 if (r < 0)
@@ -1346,6 +1352,7 @@
 }

 int bus_process_object(sd_bus *bus, sd_bus_message *m) {
+        _cleanup_free_ char *prefix = NULL;
         int r;
         size_t pl;
         bool found_object = false;
@@ -1370,9 +1377,12 @@
         assert(m->member);

         pl = strlen(m->path);
-        do {
-                char prefix[pl+1];
+        assert(pl <= BUS_PATH_SIZE_MAX);
+        prefix = new(char, pl + 1);
+        if (!prefix)
+                return -ENOMEM;

+        do {
                 bus->nodes_modified = false;

                 r = object_find_and_run(bus, m, m->path, false, &found_object);
@@ -1499,9 +1509,15 @@

         n = hashmap_get(bus->nodes, path);
         if (!n) {
-                char *prefix;
+                _cleanup_free_ char *prefix = NULL;
+                size_t pl;
+
+                pl = strlen(path);
+                assert(pl <= BUS_PATH_SIZE_MAX);
+                prefix = new(char, pl + 1);
+                if (!prefix)
+                        return -ENOMEM;

-                prefix = alloca(strlen(path) + 1);
                 OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
                         n = hashmap_get(bus->nodes, prefix);
                         if (n)
@@ -2091,8 +2107,9 @@
                 char **names) {

         BUS_DONT_DESTROY(bus);
+        _cleanup_free_ char *prefix = NULL;
         bool found_interface = false;
-        char *prefix;
+        size_t pl;
         int r;

         assert_return(bus, -EINVAL);
@@ -2111,6 +2128,12 @@
         if (names && names[0] == NULL)
                 return 0;

+        pl = strlen(path);
+        assert(pl <= BUS_PATH_SIZE_MAX);
+        prefix = new(char, pl + 1);
+        if (!prefix)
+                return -ENOMEM;
+
         do {
                 bus->nodes_modified = false;

@@ -2120,7 +2143,6 @@
                 if (bus->nodes_modified)
                         continue;

-                prefix = alloca(strlen(path) + 1);
                 OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
                         r = emit_properties_changed_on_interface(bus, prefix, path, interface, true, &found_interface, names);
                         if (r != 0)
@@ -2252,7 +2274,8 @@

 static int object_added_append_all(sd_bus *bus, sd_bus_message *m, const char *path) {
         _cleanup_set_free_ Set *s = NULL;
-        char *prefix;
+        _cleanup_free_ char *prefix = NULL;
+        size_t pl;
         int r;

         assert(bus);
@@ -2297,7 +2320,12 @@
         if (bus->nodes_modified)
                 return 0;

-        prefix = alloca(strlen(path) + 1);
+        pl = strlen(path);
+        assert(pl <= BUS_PATH_SIZE_MAX);
+        prefix = new(char, pl + 1);
+        if (!prefix)
+                return -ENOMEM;
+
         OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
                 r = object_added_append_all_prefix(bus, m, s, prefix, path, true);
                 if (r < 0)
@@ -2436,7 +2464,8 @@

 static int object_removed_append_all(sd_bus *bus, sd_bus_message *m, const char *path) {
         _cleanup_set_free_ Set *s = NULL;
-        char *prefix;
+        _cleanup_free_ char *prefix = NULL;
+        size_t pl;
         int r;

         assert(bus);
@@ -2468,7 +2497,12 @@
         if (bus->nodes_modified)
                 return 0;

-        prefix = alloca(strlen(path) + 1);
+        pl = strlen(path);
+        assert(pl <= BUS_PATH_SIZE_MAX);
+        prefix = new(char, pl + 1);
+        if (!prefix)
+                return -ENOMEM;
+
         OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
                 r = object_removed_append_all_prefix(bus, m, s, prefix, path, true);
                 if (r < 0)
@@ -2618,7 +2652,8 @@
                 const char *path,
                 const char *interface) {

-        char *prefix;
+        _cleanup_free_ char *prefix = NULL;
+        size_t pl;
         int r;

         assert(bus);
@@ -2632,7 +2667,12 @@
         if (bus->nodes_modified)
                 return 0;

-        prefix = alloca(strlen(path) + 1);
+        pl = strlen(path);
+        assert(pl <= BUS_PATH_SIZE_MAX);
+        prefix = new(char, pl + 1);
+        if (!prefix)
+                return -ENOMEM;
+
         OBJECT_PATH_FOREACH_PREFIX(prefix, path) {
                 r = interfaces_added_append_one_prefix(bus, m, prefix, path, interface, true);
                 if (r != 0)