diff --git a/src/core/socket.c b/src/core/socket.c
index 891276fd508..0fd1ad144b0 100644
--- a/src/core/socket.c
+++ b/src/core/socket.c
@@ -2597,6 +2597,7 @@ static int socket_serialize(Unit *u, FILE *f, FDSet *fds) {
 
 static int socket_deserialize_item(Unit *u, const char *key, const char *value, FDSet *fds) {
         Socket *s = SOCKET(u);
+        int r;
 
         assert(u);
         assert(key);
@@ -2651,124 +2652,183 @@ static int socket_deserialize_item(Unit *u, const char *key, const char *value,
                         s->control_command = s->exec_command[id];
                 }
         } else if (streq(key, "fifo")) {
-                int fd, skip = 0;
+                _cleanup_free_ char *fdv = NULL;
+                bool found = false;
+                int fd;
 
-                if (sscanf(value, "%i %n", &fd, &skip) < 1 || fd < 0 || !fdset_contains(fds, fd))
+                r = extract_first_word(&value, &fdv, NULL, 0);
+                if (r <= 0) {
                         log_unit_debug(u, "Failed to parse fifo value: %s", value);
-                else {
-                        bool found = false;
-
-                        LIST_FOREACH(port, p, s->ports)
-                                if (p->fd < 0 &&
-                                    p->type == SOCKET_FIFO &&
-                                    path_equal_or_files_same(p->path, value+skip, 0)) {
-                                        p->fd = fdset_remove(fds, fd);
-                                        found = true;
-                                        break;
-                                }
-                        if (!found)
-                                log_unit_debug(u, "No matching fifo socket found: %s", value+skip);
+                        return 0;
                 }
 
+                fd = parse_fd(fdv);
+                if (fd < 0 || !fdset_contains(fds, fd)) {
+                        log_unit_debug(u, "Invalid fifo value: %s", fdv);
+                        return 0;
+                }
+
+                LIST_FOREACH(port, p, s->ports)
+                        if (p->fd < 0 &&
+                            p->type == SOCKET_FIFO &&
+                            path_equal_or_files_same(p->path, value, 0)) {
+                                p->fd = fdset_remove(fds, fd);
+                                found = true;
+                                break;
+                        }
+                if (!found)
+                        log_unit_debug(u, "No matching fifo socket found: %s", value);
+
         } else if (streq(key, "special")) {
-                int fd, skip = 0;
+                _cleanup_free_ char *fdv = NULL;
+                bool found = false;
+                int fd;
 
-                if (sscanf(value, "%i %n", &fd, &skip) < 1 || fd < 0 || !fdset_contains(fds, fd))
+                r = extract_first_word(&value, &fdv, NULL, 0);
+                if (r <= 0) {
                         log_unit_debug(u, "Failed to parse special value: %s", value);
-                else {
-                        bool found = false;
-
-                        LIST_FOREACH(port, p, s->ports)
-                                if (p->fd < 0 &&
-                                    p->type == SOCKET_SPECIAL &&
-                                    path_equal_or_files_same(p->path, value+skip, 0)) {
-                                        p->fd = fdset_remove(fds, fd);
-                                        found = true;
-                                        break;
-                                }
-                        if (!found)
-                                log_unit_debug(u, "No matching special socket found: %s", value+skip);
+                        return 0;
                 }
 
+                fd = parse_fd(fdv);
+                if (fd < 0 || !fdset_contains(fds, fd)) {
+                        log_unit_debug(u, "Invalid special value: %s", fdv);
+                        return 0;
+                }
+
+                LIST_FOREACH(port, p, s->ports)
+                        if (p->fd < 0 &&
+                            p->type == SOCKET_SPECIAL &&
+                            path_equal_or_files_same(p->path, value, 0)) {
+                                p->fd = fdset_remove(fds, fd);
+                                found = true;
+                                break;
+                        }
+                if (!found)
+                        log_unit_debug(u, "No matching special socket found: %s", value);
+
         } else if (streq(key, "mqueue")) {
-                int fd, skip = 0;
+                _cleanup_free_ char *fdv = NULL;
+                bool found = false;
+                int fd;
 
-                if (sscanf(value, "%i %n", &fd, &skip) < 1 || fd < 0 || !fdset_contains(fds, fd))
+                r = extract_first_word(&value, &fdv, NULL, 0);
+                if (r <= 0) {
                         log_unit_debug(u, "Failed to parse mqueue value: %s", value);
-                else {
-                        bool found = false;
-
-                        LIST_FOREACH(port, p, s->ports)
-                                if (p->fd < 0 &&
-                                    p->type == SOCKET_MQUEUE &&
-                                    streq(p->path, value+skip)) {
-                                        p->fd = fdset_remove(fds, fd);
-                                        found = true;
-                                        break;
-                                }
-                        if (!found)
-                                log_unit_debug(u, "No matching mqueue socket found: %s", value+skip);
+                        return 0;
                 }
 
+                fd = parse_fd(fdv);
+                if (fd < 0 || !fdset_contains(fds, fd)) {
+                        log_unit_debug(u, "Invalid mqueue value: %s", fdv);
+                        return 0;
+                }
+
+                LIST_FOREACH(port, p, s->ports)
+                        if (p->fd < 0 &&
+                            p->type == SOCKET_MQUEUE &&
+                            streq(p->path, value)) {
+                                p->fd = fdset_remove(fds, fd);
+                                found = true;
+                                break;
+                        }
+                if (!found)
+                        log_unit_debug(u, "No matching mqueue socket found: %s", value);
+
         } else if (streq(key, "socket")) {
-                int fd, type, skip = 0;
+                _cleanup_free_ char *fdv = NULL, *typev = NULL;
+                bool found = false;
+                int fd, type;
 
-                if (sscanf(value, "%i %i %n", &fd, &type, &skip) < 2 || fd < 0 || type < 0 || !fdset_contains(fds, fd))
-                        log_unit_debug(u, "Failed to parse socket value: %s", value);
-                else {
-                        bool found = false;
-
-                        LIST_FOREACH(port, p, s->ports)
-                                if (p->fd < 0 &&
-                                    socket_address_is(&p->address, value+skip, type)) {
-                                        p->fd = fdset_remove(fds, fd);
-                                        found = true;
-                                        break;
-                                }
-                        if (!found)
-                                log_unit_debug(u, "No matching %s socket found: %s",
-                                               socket_address_type_to_string(type), value+skip);
+                r = extract_first_word(&value, &fdv, NULL, 0);
+                if (r <= 0) {
+                        log_unit_debug(u, "Failed to parse socket fd from value: %s", value);
+                        return 0;
                 }
 
+                fd = parse_fd(fdv);
+                if (fd < 0 || !fdset_contains(fds, fd)) {
+                        log_unit_debug(u, "Invalid socket fd: %s", fdv);
+                        return 0;
+                }
+
+                r = extract_first_word(&value, &typev, NULL, 0);
+                if (r <= 0) {
+                        log_unit_debug(u, "Failed to parse socket type from value: %s", value);
+                        return 0;
+                }
+
+                if (safe_atoi(typev, &type) < 0 || type < 0) {
+                        log_unit_debug(u, "Invalid socket type: %s", typev);
+                        return 0;
+                }
+
+                LIST_FOREACH(port, p, s->ports)
+                        if (p->fd < 0 &&
+                            socket_address_is(&p->address, value, type)) {
+                                p->fd = fdset_remove(fds, fd);
+                                found = true;
+                                break;
+                        }
+                if (!found)
+                        log_unit_debug(u, "No matching %s socket found: %s",
+                                       socket_address_type_to_string(type), value);
+
         } else if (streq(key, "netlink")) {
-                int fd, skip = 0;
+                _cleanup_free_ char *fdv = NULL;
+                bool found = false;
+                int fd;
 
-                if (sscanf(value, "%i %n", &fd, &skip) < 1 || fd < 0 || !fdset_contains(fds, fd))
+                r = extract_first_word(&value, &fdv, NULL, 0);
+                if (r <= 0) {
                         log_unit_debug(u, "Failed to parse socket value: %s", value);
-                else {
-                        bool found = false;
-
-                        LIST_FOREACH(port, p, s->ports)
-                                if (p->fd < 0 &&
-                                    socket_address_is_netlink(&p->address, value+skip)) {
-                                        p->fd = fdset_remove(fds, fd);
-                                        found = true;
-                                        break;
-                                }
-                        if (!found)
-                                log_unit_debug(u, "No matching netlink socket found: %s", value+skip);
+                        return 0;
                 }
 
+                fd = parse_fd(fdv);
+                if (fd < 0 || !fdset_contains(fds, fd)) {
+                        log_unit_debug(u, "Invalid socket value: %s", fdv);
+                        return 0;
+                }
+
+                LIST_FOREACH(port, p, s->ports)
+                        if (p->fd < 0 &&
+                            socket_address_is_netlink(&p->address, value)) {
+                                p->fd = fdset_remove(fds, fd);
+                                found = true;
+                                break;
+                        }
+                if (!found)
+                        log_unit_debug(u, "No matching netlink socket found: %s", value);
+
         } else if (streq(key, "ffs")) {
-                int fd, skip = 0;
+                _cleanup_free_ char *fdv = NULL;
+                bool found = false;
+                int fd;
 
-                if (sscanf(value, "%i %n", &fd, &skip) < 1 || fd < 0 || !fdset_contains(fds, fd))
+                r = extract_first_word(&value, &fdv, NULL, 0);
+                if (r <= 0) {
                         log_unit_debug(u, "Failed to parse ffs value: %s", value);
-                else {
-                        bool found = false;
-
-                        LIST_FOREACH(port, p, s->ports)
-                                if (p->fd < 0 &&
-                                    p->type == SOCKET_USB_FUNCTION &&
-                                    path_equal_or_files_same(p->path, value+skip, 0)) {
-                                        p->fd = fdset_remove(fds, fd);
-                                        found = true;
-                                        break;
-                                }
-                        if (!found)
-                                log_unit_debug(u, "No matching ffs socket found: %s", value+skip);
+                        return 0;
                 }
 
+                fd = parse_fd(fdv);
+                if (fd < 0 || !fdset_contains(fds, fd)) {
+                        log_unit_debug(u, "Invalid ffs value: %s", fdv);
+                        return 0;
+                }
+
+                LIST_FOREACH(port, p, s->ports)
+                        if (p->fd < 0 &&
+                            p->type == SOCKET_USB_FUNCTION &&
+                            path_equal_or_files_same(p->path, value, 0)) {
+                                p->fd = fdset_remove(fds, fd);
+                                found = true;
+                                break;
+                        }
+                if (!found)
+                        log_unit_debug(u, "No matching ffs socket found: %s", value);
+
         } else
                 log_unit_debug(UNIT(s), "Unknown serialization key: %s", key);
 
diff --git a/src/core/unit.c b/src/core/unit.c
index c7635a291c5..4e9ae6148f3 100644
--- a/src/core/unit.c
+++ b/src/core/unit.c
@@ -6162,7 +6162,9 @@ int activation_details_deserialize(const char *key, const char *value, Activatio
                         return -EINVAL;
 
                 t = unit_type_from_string(value);
-                if (t == _UNIT_TYPE_INVALID)
+                /* The activation details vtable has defined ops only for path
+                 * and timer units */
+                if (!IN_SET(t, UNIT_PATH, UNIT_TIMER))
                         return -EINVAL;
 
                 *details = malloc0(activation_details_vtable[t]->object_size);
diff --git a/src/shared/fdset.c b/src/shared/fdset.c
index d816a3e4efb..2138ffcdb92 100644
--- a/src/shared/fdset.c
+++ b/src/shared/fdset.c
@@ -77,6 +77,10 @@ int fdset_put(FDSet *s, int fd) {
         assert(s);
         assert(fd >= 0);
 
+        /* Avoid integer overflow in FD_TO_PTR() */
+        if (fd == INT_MAX)
+                return log_debug_errno(SYNTHETIC_ERRNO(EINVAL), "Refusing invalid fd: %d", fd);
+
         return set_put(MAKE_SET(s), FD_TO_PTR(fd));
 }
 
@@ -115,6 +119,12 @@ bool fdset_contains(FDSet *s, int fd) {
         assert(s);
         assert(fd >= 0);
 
+        /* Avoid integer overflow in FD_TO_PTR() */
+        if (fd == INT_MAX) {
+                log_debug("Refusing invalid fd: %d", fd);
+                return false;
+        }
+
         return !!set_get(MAKE_SET(s), FD_TO_PTR(fd));
 }
 
@@ -122,6 +132,10 @@ int fdset_remove(FDSet *s, int fd) {
         assert(s);
         assert(fd >= 0);
 
+        /* Avoid integer overflow in FD_TO_PTR() */
+        if (fd == INT_MAX)
+                return log_debug_errno(SYNTHETIC_ERRNO(ENOENT), "Refusing invalid fd: %d", fd);
+
         return set_remove(MAKE_SET(s), FD_TO_PTR(fd)) ? fd : -ENOENT;
 }
 
diff --git a/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-4847017160212480.fuzz b/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-4847017160212480.fuzz
new file mode 100644
index 00000000000..13ff22cf4dd
Binary files /dev/null and b/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-4847017160212480.fuzz differ
diff --git a/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-6018678331408384 b/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-6018678331408384
new file mode 100644
index 00000000000..d0dca3329c6
--- /dev/null
+++ b/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-6018678331408384
@@ -0,0 +1,3 @@
+
+l.socket
+socket=2147483647 5
\ No newline at end of file
diff --git a/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-6207619447259136.fuzz b/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-6207619447259136.fuzz
new file mode 100644
index 00000000000..b3f5c9bae32
--- /dev/null
+++ b/test/fuzz/fuzz-manager-serialize/clusterfuzz-testcase-minimized-fuzz-manager-serialize-6207619447259136.fuzz
@@ -0,0 +1,4 @@
+
+d.socket
+job
+activation-details-unit-type=service
\ No newline at end of file