alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"GPL WEB_CLIENT libpng tRNS overflow attempt"; flow:to_client,established; content:"|89|PNG|0D 0A 1A 0A|"; content:"IHDR"; within:4; distance:4; content:"tRNS"; distance:0; byte_test:4,>,256,-8,relative,big; pcre:"/IHDR(?!.*?PLTE).*?tRNS/s"; reference:bugtraq,10872; reference:cve,2004-0597; classtype:attempted-user; sid:2102673; rev:6; metadata:affected_product Web_Browsers, affected_product Web_Browser_Plugins, attack_target Client_Endpoint, created_at 2010_09_23, deployment Perimeter, confidence Medium, signature_severity Major, tag Web_Client_Attacks, updated_at 2019_07_26;)