日历归档 |
|
<< < 2024 - 12 > >> | Su | Mo | Tu | We | Th | Fr | Sa | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 |
|
|
|
About Me |
|
|
ZhangSichu |
|
Male |
|
32 |
|
ZhangSichu@gmail.com |
|
ZhangSichu@hotmail.com |
|
ZhangSichu.com |
|
weibo.com/zhangsichu |
|
|
|
个人推荐 |
|
|
|
|
分类归档 |
|
|
|
|
My Friends |
|
|
|
|
浅谈javascript函数劫持[转载]
|
一篇非常好的javascript Function应用文章。 原文地址: http://www.xfocus.net/articles/200712/963.html
-----------------------------------------------------------------------------------------------
一、概述
javascript函数劫持,也就是老外提到的javascript hijacking技术。最早还是和剑心同学讨论问题时偶然看到的一段代码,大概这样写的: window.alert = function(s) {}; 觉得这种用法很巧妙新颖,和API Hook异曲同工,索性称之为javascript function hook,也就是函数劫持。通过替换js函数的实现来达到劫持这个函数调用的目的,一个完整的hook alert函数例子如下:
<!--1.htm--> <script type="text/javascript"> <!-- var _alert = alert; window.alert = function(s) { if (confirm("是否要弹框框,内容是\"" + s + "\"?")) { _alert(s); } } //--> </script> <html> <body> <input type="button" onclick="javascript: alert(Hello World!)" value="test" /> </body> </html>
|
搞过API Hook的同学们看到这个代码一定会心的一笑,先保存原函数实现,然后替换为我们自己的函数实现,添加我们自己的处理逻辑后最终再调用原来的函数实现,这样这个alert函数就被我们劫持了。原理非常简单,下面举些典型的应用来看看我们能利用它来做些什么。
二、应用举例
1. 实现一个简易的javascript debugger,这里说是debugger比较标题党,其实只是有点类似于debugger的功能,主要利用js函数劫持来实现函数的break point,来看看个简单的例子:
<script type="text/javascript"> <!-- var _eval = eval; eval = function(s) { if (confirm("eval被调用\n\n调用函数\n" + eval.caller + "\n\n调用参数\n" + s)) { _eval(s); } } //--> </script> <html> <head> </head> <body> <script type="text/javascript"> <!-- function test() { var a = "alert(1)"; eval(a); }
function t() { test(); }
t(); //--> </script> </body> </html>
|
通过js函数劫持中断函数执行,并显示参数和函数调用者代码,来看一个完整例子的效果:
>help debug commands:
bp <function name> - set a breakpoint on a function, e.g. "bp window.alert". bl - list all breakpoints. bc <breakpoint number> - remove a breakpoint by specified number, e.g. "bc 0". help - help information.
>bp window.alert * breakpoint on function "window.alert" added successfully.
>bl * 1 breakpoints: 0 - window.alert
>bc 0 * breakpoint on function "window.alert" deleted successfully.
|
这里演示设置断点,察看断点和删除断点,完整代码在本文附录[1]给出。
2. 设置陷阱实时捕捉跨站测试者,搞跨站的人总习惯用alert来确认是否存在跨站,如果你要监控是否有人在测试你的网站xss的话,可以在你要监控的页面里hook alert函数,记录alert调用情况:
<script type="text/javascript"> <!-- function log(s) { var img = new Image(); img.style.width = img.style.height = 0; img.src = "http://yousite.com/log.php?caller=" + encodeURIComponent(s); }
var _alert = alert; window.alert = function(s) { log(alert.caller); _alert(s); } //--> </script>
|
当然,你这个函数要加到页面的最开始,而且还要比较隐蔽一些,赫赫,你甚至可以使alert不弹框或者弹个警告框,让测试者抓狂一把。
3. 实现DOM XSS自动化扫描,目前一般的XSS自动化扫描的方法是从http返回结果中搜索特征来确定是否存在漏洞,但是这种方法不适用于扫描DOM XSS,因为DOM XSS是由客户端脚本造成的,比如前段时间剑心发现的google的跨站(见附录[2])原理如下:
document.write(document.location.hash);
|
这样的跨站无法反映在http response里,所以传统扫描方法没法扫描出来。但是如果你从上个例子里受到启发的话,一定会想到设置陷阱的办法,DOM XSS最终导致alert被执行,所以我们hook alert函数设置陷阱,如果XSS成功则会去调用alert函数,触发我们的陷阱记录结果,这样就可以实现DOM XSS的自动化扫描,陷阱代码类似于上面。
4. 灵活的使用js劫持辅助你的页面代码分析工作,比如分析网页木马时,经常会有通过eval或者document.write来进行加密的情况,于是我们编写段hook eval和document.write的小工具,辅助解密:
<script type="text/javascript"> <!-- var _eval = eval; eval = window.execScript = window.document.write = window.document.writeln = function(s) { document.getElementById("output").value = s; } //--> </script> <html> <body> input: <!--<textarea id="input" cols="80" rows="10"></textarea>--> <input type="button" onclick="javascript: _eval(document.getElementById(input).value);" value="decode" /> <br /> output: <!--<textarea id="output" cols="80" rows="10"></textarea>--> </body> </html>
|
在input框里输入加密的代码:
eval(unescape("%61%6C%65%72%74%28%31%29%3B"));
|
在output框里输出解码后的代码:
当然你还能想到更多的灵活应用:)
三、反劫持
谈到劫持也就必然要谈谈反劫持的话题,假设你要写一个健壮的xss playload,就需要考虑反劫持,有两个问题要解决:
如何判断是否被劫持了? 如果发现被劫持了,如何反劫持?
1. 判断某个函数是否被劫持,这个好办,写个小程序对比一下一个函数被hook前后,有什么差别:
<!--<textarea id="tb1" cols="80" rows="8"></textarea>--> <script type="text/javascript"> <!-- document.getElementById("tb1").value = eval + "\n"; var _eval = eval; eval = function(s) { alert(s); _eval(s); } document.getElementById("tb1").value += eval; //--> </script>
|
结果:
function eval() { [native code] }
function(s) { alert(s); _eval(s); }
|
我们发现那些内置函数是[native code],而自定义的则是具体的函数定义,用这个特征就可以简单的检测函数是否被劫持:
function checkHook(proc) { if (proc.toString().indexOf("[native code]") > 0) { return false; } else { return true; } }
|
2. 如何反劫持,第一个想法就是恢复被劫持的函数,如果劫持的人把原函数保存在某个变量里那还好办,直接调用原函数就可以了,但是劫持者自己也没保存副本怎么办,只能自己创建个新的环境,然后用新环境里的干净的函数来恢复我们这里被hook了的,怎么创建新环境?整个新的iframe好了,里面就是个全新的环境。ok,动手吧:
function unHook(proc) { var f = document.createElement("iframe"); f.style.border = "0"; f.style.width = "0"; f.style.height = "0"; document.body.appendChild(f);
var d = f.contentWindow.document; d.write("<script type=\"text/javascript\">window.parent.escape = escape;<\/script>"); d.close(); }
|
综合1、2节,整个测试代码如下:
<!--antihook.htm--> <script type="text/javascript"> <!-- escape = function(s) { return s; } //--> </script> <html> <body> <input type="button" onclick="javascript: test();" value="test" /> <script type="text/javascript"> <!-- function test() { alert(escape("s y")); if (checkHook(escape)) { unHook(escape); }
alert(escape("s y")); }
function checkHook(proc) { if (proc.toString().indexOf("[native code]") > 0) { return false; } else { return true; } }
function unHook(proc) { var f = document.createElement("iframe"); f.style.border = "0"; f.style.width = "0"; f.style.height = "0"; document.body.appendChild(f);
var d = f.contentWindow.document; d.write("<script type=\"text/javascript\">window.parent.escape = escape;<\/script>"); d.close(); } //--> </script> </body> </html>
|
3. 不是上面两个问题都解决了么,为什么要有第3节?因为那不是个最好的解决办法,既然我们可以创建全新的iframe,何不把代码直接放到全新iframe 里执行呢,这样做的话绿色环保,既不用考虑当前context里的hook问题,也不用改动当前context,不会影响本身的程序执行。给出两个比较通用点的函数:
function createIframe(w) { var d = w.document; var newIframe = d.createElement("iframe"); newIframe.style.width = 0; newIframe.style.height = 0; d.body.appendChild(newIframe); newIframe.contentWindow.document.write("<html><body></body></html>"); return newIframe; }
function injectScriptIntoIframe(f, proc) { var d = f.contentWindow.document; var s = "<script>\n(" + proc.toString() + ")();\n</script>"; d.write(s); }
把你的payload封装进一个函数,然后调用这两个方法来在iframe里执行:
function payload() { // your code goes here }
var f = createIframe(top); injectScriptIntoIframe(f, payload);
|
四、最后
由于国内很少有见文章提及这个东西,所以才草成这篇,希望能够抛砖引玉。由于本人水平有限,难免有错误或者疏漏之处请谅解,没有说清楚的地方,欢迎和我交流。
还有就是一些不得不感谢的人,感谢剑心一直以来毫无保留的交流,感谢黑锅多次鼓励我把自己的心得体会写成文字,感谢幻影所有的朋友们、B.C.T的朋友们以及群里那帮经常一起扯淡的朋友们。
广告一下,没法幻影blog的朋友,可以添加hosts来突破: 72.14.219.190 pstgroup.blogspot.com
五、附录
[1] 简易的javascript inline debugger代码
<!--test.htm--> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head><title>Javascript Inline Debugger</title></head> <body> <script language="javascript" type="text/javascript" src="js_inline_debugger.js"></script> <input type="button" value="hahaha" onclick="javascript: alert(this.value);" style="margin-left: 300px;" /> </body> </html>
/* FileName: js_inline_debugger.js Author: luoluo Contact: luoluonet_at_yahoo.cn Date: 2007-6-27 Version: 0.1 Usage: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> </head> <body> <script language="javascript" type="text/javascript" src="js_inline_debugger.js"></script> </body> </html> Instruction: It is a simple javascript inline debugger. You must add xhtml1-transitional dtd to your html document if you wanna to use the script. */
//--------------------------------------------------------------------------// // 公用的函数 //--------------------------------------------------------------------------// // 判断是否是IE function isIE() { return document.all && window.external; }
// 去除字符串两边的空格 String.prototype.trim = function() { var re = /(^\s*)|(\s*)$/g; return this.replace(re, ""); }
// 删除数组中某个元素 Array.prototype.remove = function(i) { var o = this[i]; for (var j = i; j < this.length - 1; j ++) { this[j] = this[j + 1]; } -- this.length; return o; }
// 判断一个数组中是否存在相同的元素 Array.prototype.search = function(o) { for (var i = 0; i < this.length; i ++) { if (this[i] == o) { return i; } }
return -1; }
// html编码 function htmlEncode(s) { s = s.replace(/&/g, "&"); s = s.replace(/</g, "<"); s = s.replace(/>/g, ">"); s = s.replace(/\"/g, """); s = s.replace(/\/g, """);
return s; }
// js编码 function jsEncode(s) { s = s.replace(/\\/g, "\\\\"); s = s.replace(/\n/g, "\\n"); s = s.replace(/\"/g, "\\\""); s = s.replace(/\/g, "\\\"); return s; }
//--------------------------------------------------------------// // 命令行窗口工具 //--------------------------------------------------------------// function Console(parentNode, processInputProc) { // 窗口 var panel = document.createElement("div"); panel.style.width = "250px"; panel.style.height = "250px"; panel.style.borderColor = "#666666"; panel.style.borderWidth = "1px"; panel.style.backgroundColor = "#ffffff"; panel.style.borderStyle = "solid"; panel.style.position = "absolute"; panel.style.zIndex = 100; parentNode.appendChild(panel);
// 标题栏 var title = document.createElement("div"); title.style.width = "250px"; title.style.height = "15px"; title.style.backgroundColor = "#dddddd"; title.style.fontSize = "12px"; title.style.fontFamily = "verdana,tahoma"; panel.appendChild(title);
// 标题栏拖动窗口功能 var isDragging = false; var startPos = new Position(panel.offsetLeft, panel.offsetTop); var startMousePos = new Position(0, 0);
title.onmouseover = function(evt) { this.style.cursor = "pointer"; }
title.onmousedown = function(evt) { if (isDragging == true) { return; }
var event = evt || window.event; startMousePos.x = event.clientX; startMousePos.y = event.clientY; isDragging = true; }
title.onmousemove = function(evt) { if (isDragging == false) { return; } activateWindow(); var event = evt || window.event; panel.style.left = (event.clientX - startMousePos.x) + startPos.x + "px"; panel.style.top = (event.clientY - startMousePos.y) + startPos.y + "px"; }
title.onmouseup = function(evt) { if (isDragging == false) { return; }
var event = evt || window.event; startPos.x = (event.clientX - startMousePos.x) + startPos.x; panel.style.left = startPos.x + "px"; startPos.y = (event.clientY - startMousePos.y) + startPos.y; panel.style.top = startPos.y + "px"; isDragging = false; }
// 关闭窗口功能 var closeButton = document.createElement("div"); closeButton.style.width = "13px"; closeButton.style.height = "13px"; closeButton.style.backgroundColor = "#ffffff"; closeButton.style.styleFloat = closeButton.style.cssFloat = "left"; closeButton.style.fontSize = "12px"; closeButton.style.borderWidth = "1px"; closeButton.style.borderColor = "#999999"; closeButton.style.borderStyle = "solid"; closeButton.style.paddingButton = "2px"; closeButton.innerHTML = "<div style=\"margin-top: -2px;margin-left: 3px;\">x</div>"; title.appendChild(closeButton);
var isVisible = true;
// 窗口关闭 closeButton.onclick = function(evt) { isVisible = false; panel.style.display = "none"; }
// 标题栏文字 var titleLabel = document.createElement("div"); titleLabel.style.height = "14px"; titleLabel.style.width = "200px"; titleLabel.style.fontSize = "11px"; titleLabel.style.color = "#ffffff"; titleLabel.style.styleFloat = titleLabel.style.cssFloat = "left"; titleLabel.style.fontFamily = "verdana,tahoma"; titleLabel.innerHTML = "Javascript Inline Debugger"; //titleLabel.style.marginTop = isIE() ? -14 : "-14px"; titleLabel.style.marginLeft = isIE() ? 18 : "18px"; title.appendChild(titleLabel);
// 中间的显示部分 var showPanel = document.createElement("div"); showPanel.style.width = "250px"; showPanel.style.height = isIE() ? "221px" : "219px"; showPanel.style.fontSize = "11px"; showPanel.style.padding = "0"; showPanel.style.margin = "0"; showPanel.style.overflow = "auto"; showPanel.style.marginTop = isIE() ? -1 : "0"; panel.appendChild(showPanel);
// 命令输入框 var cmdArea = document.createElement("div"); panel.appendChild(cmdArea);
var cmdTextbox = document.createElement("input"); cmdTextbox.type = "text"; cmdTextbox.style.width = "250px"; cmdTextbox.style.height = "12px"; cmdTextbox.style.fontSize = "12px"; cmdTextbox.style.padding = "0"; cmdTextbox.style.margin = "0"; cmdTextbox.style.marginTop = isIE() ? -2 : "0"; cmdTextbox.style.borderWidth = "0"; cmdTextbox.style.borderTopWidth = "1px"; cmdTextbox.style.paddingTop = "2px"; cmdArea.appendChild(cmdTextbox);
// 窗口激活或者不激活 var isActive = false;
// 激活窗口 var activateWindow = function() { if (! isVisible) { return; }
if (isActive) { return; }
cmdTextbox.focus(); title.style.backgroundColor = "#015DF4"; isActive = true; }
panel.onclick = activateWindow;
// 不激活窗口 var deactivateWindow = function() { if (! isVisible) { return; }
if (! isActive) { return; }
title.style.backgroundColor = "#cccccc"; isActive = false; }
cmdTextbox.onfocus = activateWindow; cmdTextbox.onblur = deactivateWindow;
// 输出函数 var dbgPrint = function(s) { showPanel.innerHTML += htmlEncode(s).replace(/\n|(\r\n)/g, "<br />"); if (parseInt(showPanel.scrollHeight) > parseInt(showPanel.style.height)) { showPanel.scrollTop += parseInt(showPanel.scrollHeight) - parseInt(showPanel.style.height); } }
// 调用输入处理回调函数 cmdTextbox.onkeydown = function(evt) { var event = evt || window.event;
if (event.keyCode == 0x0d) { processInputProc(this.value, dbgPrint); this.value = ""; } } }
// 坐标类 function Position(x, y) { this.x = x; this.y = y; }
//--------------------------------------------------------------------------// // 内联调试器类 //--------------------------------------------------------------------------// function InlineDebugger() { var bpList = new Array(); var id_eval;
// 设置断点 var bp = function(funcName) { // 检查eval是否被hook if ((new String(eval)).indexOf("[native code]") < 0) { return "error: eval function was hooked by other codes in the front.\n"; }
// 保存未被hooked的eval id_eval = eval;
var re = /^[a-zA-Z0-9_\.]+$/i; if (! re.test(funcName)) { return "error: bad argument of command bp \"" + funcName + "\".\n"; }
try { id_eval("if (typeof(" + funcName + ") == \"object\" || typeof(" + funcName + ") == \"function\") {var obj = " + funcName + ";}"); } catch (e) { return "error: " + e + ", invalid function name \"" + funcName + "\".\n"; }
if (obj == undefined) { return "error: the argument of command bp \"" + funcName + "\" is not a function object.\n"; }
if ((new String(obj)).indexOf("function") < 0) { return "error: the argument of command bp \"" + funcName + "\" is a property, a function is required.\n"; }
if (bpList.search(funcName) >= 0) { return "error: there is a breakpoint on function \"" + funcName + "\"\n"; }
try { var sc = "window." + funcName.replace(/\./g, "_") + "_bak = " + funcName + ";\n" + funcName + " = " + "function() {\n" + " var args = \"\";\n" + " for (var i = 0; i < arguments.length; i ++) {\n" + " args += arguments[i] + (i == (arguments.length - 1) ? \"\" : \",\");\n" + " }\n" + " if (confirm(\"function \\\"" + funcName + "\\\" was called, execute it?\\n\\narguments:\\n\" + args + \"\\n\\ncaller:\\n\" + " + funcName + ".caller)) {\n" + " id_eval(\"" + funcName.replace(/\./g, "_") + "_bak(\\\"\" + jsEncode(args) + \"\\\")\");\n" + " }\n" + "};" + "\n"; id_eval(sc); bpList.push(funcName); return "* breakpoint on function \"" + funcName + "\" added successfully.\n"; } catch (e) { return "unkown error: " + e + ".\n"; } }
// 枚举所有的断点 var bl = function() { if (bpList.length == 0) { return "* no breakpoint.\n"; }
var bps = "* " + bpList.length + " breakpoints: \n";
for (var i = 0; i < bpList.length; i ++) { bps += i + " - " + bpList[i] + "\n"; }
return bps; }
// 清除某个断点 var bc = function(n) { try { n = parseInt(n); } catch (e) { return "error: bc command requires a numeric argument.\n"; }
if (bpList.length == 0) { return "error: no breakpoint.\n"; }
var funcName = bpList.remove(n); try { eval(funcName + " = window." + funcName.replace(/\./g, "_") + "_bak;"); return "* breakpoint on function \"" + funcName + "\" deleted successfully.\n"; } catch (e) { return "error: " + e + ".\n"; } }
// 帮助 var help = function() { var s = "debug commands:\n\n" + "bp <function name> - set a breakpoint on a function, e.g. \"bp window.alert\".\n" + "bl - list all breakpoints.\n" + "bc <breakpoint number> - remove a breakpoint by specified number, e.g. \"bc 0\".\n" + "help - help information.\n" "\n"; return s; }
// 处理命令 this.exeCmd = function(cmd) { cmd = cmd.trim(); var cmdParts = cmd.split(/\s+/g); var cmdName; var cmdArg;
if (cmdParts.length == 1) { cmdName = cmd; } else { cmdName = cmdParts[0]; cmdArg = cmdParts[1]; }
switch (cmdName) { case "bp": if (cmdArg == undefined) { return "error: bp command requires an argument.\n"; } else { return bp(cmdArg); } break;
case "bl": return bl(); break;
case "bc": if (cmdArg == undefined) { return "error: bc command requires an argument \"number of breakpoint\".\n"; } else { return bc(cmdArg); } break;
case "help": return help(); break;
default: return "error: command \"" + cmdName + "\" not found, you can get information by \"help\" command.\n"; break; } } }
//-----------------------------------------------------------------------------// // 主过程 //-----------------------------------------------------------------------------// /*try { debugger; } catch (e) {}*/ var id = new InlineDebugger(); var console = new Console(document.body, function(s, printProc){printProc(id.exeCmd(s));});
|
|
|
|
|
|
|