--- sys/fs/nfs/nfs_commonsubs.c	2021-11-30 15:04:30.022049000 -0800
+++ sys/fs/nfs/nfs_commonsubs.c	2021-11-30 16:24:39.205303000 -0800
@@ -1108,6 +1108,14 @@ nfsrv_dissectacl(struct nfsrv_descript *nd, NFSACL_T *
 	NFSM_DISSECT(tl, u_int32_t *, NFSX_UNSIGNED);
 	aclsize = NFSX_UNSIGNED;
 	acecnt = fxdr_unsigned(int, *tl);
+	/*
+	 * The RFCs do not define a fixed limit to the number of ACEs in
+	 * an ACL, but 10240 should be more than sufficient.
+	 */
+	if (acecnt < 0 || acecnt > 10240) {
+		error = NFSERR_BADXDR;
+		goto nfsmout;
+	}
 	if (acecnt > ACL_MAX_ENTRIES)
 		aceerr = NFSERR_ATTRNOTSUPP;
 	if (nfsrv_useacl == 0)
@@ -1493,6 +1501,8 @@ nfsv4_loadattr(struct nfsrv_descript *nd, vnode_t vp,
 			    } else {
 				error = nfsrv_dissectacl(nd, NULL, &aceerr,
 				    &cnt, p);
+				if (error)
+				    goto nfsmout;
 				*retcmpp = NFSERR_ATTRNOTSUPP;
 			    }
 			  }
--- sys/fs/nfs/nfs_commonacl.c	2021-11-30 15:48:22.026291000 -0800
+++ sys/fs/nfs/nfs_commonacl.c	2021-11-30 15:50:12.720713000 -0800
@@ -58,7 +58,11 @@ nfsrv_dissectace(struct nfsrv_descript *nd, struct acl
 	flag = fxdr_unsigned(u_int32_t, *tl++);
 	mask = fxdr_unsigned(u_int32_t, *tl++);
 	len = fxdr_unsigned(int, *tl);
-	if (len < 0) {
+	/*
+	 * The RFCs do not specify a limit to the length of the "who", but
+	 * NFSV4_OPAQUELIMIT (1024) should be sufficient.
+	 */
+	if (len < 0 || len > NFSV4_OPAQUELIMIT) {
 		error = NFSERR_BADXDR;
 		goto nfsmout;
 	} else if (len == 0) {