diff --git a/src/network/netdev/macsec.c b/src/network/netdev/macsec.c
index 6d17d45059a..98927b168da 100644
--- a/src/network/netdev/macsec.c
+++ b/src/network/netdev/macsec.c
@@ -959,15 +959,19 @@ static int macsec_read_key_file(NetDev *netdev, SecurityAssociation *sa) {
                 return 0;
 
         r = read_full_file_full(
-                        AT_FDCWD, sa->key_file, UINT64_MAX, SIZE_MAX,
-                        READ_FULL_FILE_SECURE | READ_FULL_FILE_UNHEX | READ_FULL_FILE_WARN_WORLD_READABLE | READ_FULL_FILE_CONNECT_SOCKET,
+                        AT_FDCWD, sa->key_file, UINT64_MAX, MACSEC_KEYID_LEN,
+                        READ_FULL_FILE_SECURE |
+                        READ_FULL_FILE_UNHEX |
+                        READ_FULL_FILE_WARN_WORLD_READABLE |
+                        READ_FULL_FILE_CONNECT_SOCKET |
+                        READ_FULL_FILE_FAIL_WHEN_LARGER,
                         NULL, (char **) &key, &key_len);
         if (r < 0)
                 return log_netdev_error_errno(netdev, r,
                                               "Failed to read key from '%s', ignoring: %m",
                                               sa->key_file);
 
-        if (key_len != 16)
+        if (key_len != MACSEC_KEYID_LEN)
                 return log_netdev_error_errno(netdev, SYNTHETIC_ERRNO(EINVAL),
                                               "Invalid key length (%zu bytes), ignoring: %m", key_len);
 
diff --git a/src/network/netdev/wireguard.c b/src/network/netdev/wireguard.c
index c89577609d4..4c7d837c412 100644
--- a/src/network/netdev/wireguard.c
+++ b/src/network/netdev/wireguard.c
@@ -1037,8 +1037,12 @@ static int wireguard_read_key_file(const char *filename, uint8_t dest[static WG_
         assert(dest);
 
         r = read_full_file_full(
-                        AT_FDCWD, filename, UINT64_MAX, SIZE_MAX,
-                        READ_FULL_FILE_SECURE | READ_FULL_FILE_UNBASE64 | READ_FULL_FILE_WARN_WORLD_READABLE | READ_FULL_FILE_CONNECT_SOCKET,
+                        AT_FDCWD, filename, UINT64_MAX, WG_KEY_LEN,
+                        READ_FULL_FILE_SECURE |
+                        READ_FULL_FILE_UNBASE64 |
+                        READ_FULL_FILE_WARN_WORLD_READABLE |
+                        READ_FULL_FILE_CONNECT_SOCKET |
+                        READ_FULL_FILE_FAIL_WHEN_LARGER,
                         NULL, &key, &key_len);
         if (r < 0)
                 return r;
diff --git a/test/fuzz/fuzz-netdev-parser/oss-fuzz-62556 b/test/fuzz/fuzz-netdev-parser/oss-fuzz-62556
new file mode 100644
index 00000000000..e2418f9e5f8
Binary files /dev/null and b/test/fuzz/fuzz-netdev-parser/oss-fuzz-62556 differ