Index: shim-0.7.318.81ee561d/MokManager.c
===================================================================
--- shim-0.7.318.81ee561d.orig/MokManager.c
+++ shim-0.7.318.81ee561d/MokManager.c
@@ -163,8 +163,18 @@ static UINT32 count_keys(void *Data, UIN
 	EFI_SIGNATURE_LIST *CertList = Data;
 	UINTN dbsize = DataSize;
 	UINT32 MokNum = 0;
+	void *end = Data + DataSize;
 
 	while ((dbsize > 0) && (dbsize >= CertList->SignatureListSize)) {
+
+		/* Use ptr arithmetics to ensure bounded access. Do not allow 0
+		 * SignatureListSize that will cause endless loop.
+		 */
+		if ((void *)(CertList + 1) > end || CertList->SignatureListSize == 0) {
+			console_notify(L"Invalid MOK detected! Ignoring MOK List.");
+			return 0;
+		}
+
 		if (CertList->SignatureListSize == 0 ||
 		    CertList->SignatureListSize <= CertList->SignatureSize) {
 			console_errorbox(L"Corrupted signature list");
@@ -192,6 +202,7 @@ static MokListNode *build_mok_list(UINT3
 	EFI_GUID CertType = X509_GUID;
 	UINTN dbsize = DataSize;
 	UINTN count = 0;
+	void *end = Data + DataSize;
 
 	list = AllocatePool(sizeof(MokListNode) * num);
 
@@ -201,12 +212,24 @@ static MokListNode *build_mok_list(UINT3
 	}
 
 	while ((dbsize > 0) && (dbsize >= CertList->SignatureListSize)) {
+		/* CertList out of bounds? */
+		if ((void *)(CertList + 1) > end || CertList->SignatureListSize == 0) {
+			FreePool(list);
+			return NULL;
+		}
+
 		/* Omit the signature check here since we already did it
 		   in count_keys() */
 
 		Cert = (EFI_SIGNATURE_DATA *) (((UINT8 *) CertList) +
 		  sizeof (EFI_SIGNATURE_LIST) + CertList->SignatureHeaderSize);
 
+		/* Cert out of bounds? */
+		if ((void *)(Cert + 1) > end || CertList->SignatureSize <= sizeof(EFI_GUID)) {
+			FreePool(list);
+			return NULL;
+		}
+
 		list[count].Type = CertList->SignatureType;
 		if (CompareGuid (&CertList->SignatureType, &CertType) == 0) {
 			list[count].MokSize = CertList->SignatureSize -
@@ -218,6 +241,12 @@ static MokListNode *build_mok_list(UINT3
 			list[count].Mok = (void *)Cert;
 		}
 
+		/* MOK out of bounds? */
+		if (list[count].MokSize > end - (void *)list[count].Mok) {
+			FreePool(list);
+			return NULL;
+		}
+
 		count++;
 		dbsize -= CertList->SignatureListSize;
 		CertList = (EFI_SIGNATURE_LIST *) ((UINT8 *) CertList +