Patch for https://github.com/relan/exfat/issues/5
See also:
https://blog.fuzzing-project.org/25-Heap-overflow-and-endless-loop-in-exfatfsck-exfat-utils.html
Index: exfat-utils/libexfat/mount.c
===================================================================
--- exfat-utils.orig/libexfat/mount.c
+++ exfat-utils/libexfat/mount.c
@@ -172,6 +172,24 @@ int exfat_mount(struct exfat* ef, const
 		exfat_error("exFAT file system is not found");
 		return -EIO;
 	}
+	/* sector cannot be smaller than 512 bytes */
+        if (ef->sb->sector_bits < 9)
+        {
+                exfat_close(ef->dev);
+                exfat_error("too small sector size: 2^%hhd", ef->sb->sector_bits);
+                free(ef->sb);
+                return -EIO;
+        }
+        /* officially exFAT supports cluster size up to 32 MB */
+        if ((int) ef->sb->sector_bits + (int) ef->sb->spc_bits > 25)
+        {
+                exfat_close(ef->dev);
+                exfat_error("too big cluster size: 2^(%hhd+%hhd)",
+                                ef->sb->sector_bits, ef->sb->spc_bits);
+                free(ef->sb);
+                return -EIO;
+        }
+
 	if (ef->sb->version.major != 1 || ef->sb->version.minor != 0)
 	{
 		exfat_close(ef->dev);
@@ -187,16 +205,6 @@ int exfat_mount(struct exfat* ef, const
 		exfat_error("unsupported FAT count: %hhu", ef->sb->fat_count);
 		return -EIO;
 	}
-	/* officially exFAT supports cluster size up to 32 MB */
-	if ((int) ef->sb->sector_bits + (int) ef->sb->spc_bits > 25)
-	{
-		exfat_close(ef->dev);
-		free(ef->sb);
-		exfat_error("too big cluster size: 2^%d",
-				(int) ef->sb->sector_bits + (int) ef->sb->spc_bits);
-		return -EIO;
-	}
-
 	ef->zero_cluster = malloc(CLUSTER_SIZE(*ef->sb));
 	if (ef->zero_cluster == NULL)
 	{