diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 605e5dc..70d9659 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2478,6 +2478,12 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg,
 		goto out;
 	}
 
+	/* RTF_CACHE is an internal flag; can not be set by userspace */
+	if (cfg->fc_flags & RTF_CACHE) {
+		NL_SET_ERR_MSG(extack, "Userspace can not set RTF_CACHE");
+		goto out;
+	}
+
 	if (cfg->fc_dst_len > 128) {
 		NL_SET_ERR_MSG(extack, "Invalid prefix length");
 		goto out;