Last week, one of my site received a bruteforce attack. When I check log/reports, I see this in my report:

a:5:{i:0;s:313:"SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (DB_Name.catalog_compare_item, CONSTRAINT FK_CAT_CMP_ITEM_PRD_ID_CAT_PRD_ENTT_ENTT_ID FOREIGN KEY (product_id) REFERENCES catalog_product_entity (entity_id) ON DELETE CA)";i:1;s:2627:"#0 /lib/Varien/Db/Statement/Pdo/Mysql.php(110): Zend_Db_Statement_Pdo->_execute(Array)

{main}";s:3:"url";s:451:"/catalog/product_compare/index/items/495,543,1957,1960,1963,2192,2195,2593,2643,5656,5659,5663,5667,5670,6913,6914,6915,6916,6917,6918,6919,6920,6964,6965,6966,6967,6968,6969,6970,6971,6975,6978,6979,6980,6986,8319,9386,9397,9467,9470,9473,9476,9895,..%c0%af..%c0%af..%c0%af..%c0%af..%c0%af..%c0%af..%c0%af..%c0%afetc/passwd/uenc/aHR0cHM6Ly93d3cuZGlnaXRhbGNpbmVtYS5jb20uYXUvY2xlYXJhbmNlP3Bvd2VyX2FtcF9zcGVha2VyX2NoYW5uZWw9MzAxJmFtcDtwcmljZT0xNTAwLQ,,/";s:11:"script_name";s:10:"/index.php";s:4:"skin";s:7:"default";}

Interestingly, these lines are different for each report:

/%5c../%5c../%5c../%5c../%5c../%5c../%5c../etc/passwd/uenc/

..%c0%af..%c0%af..%c0%af..%c0%af..%c0%af..%c0%af..%c0%af..%c0%afetc/passwd/uenc

Are there any known vulnerability in compare function? How can we deal with this?