# Bypassing SOP with Iframes - 2
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## Iframes in SOP-2
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.
Katika changamoto hii, mshambuliaji anahitaji **bypass** hii:
```javascript
if (e.source == window.calc.contentWindow && e.data.token == window.token) {
```
Ikiwa atafanya hivyo, anaweza kutuma **postmessage** yenye maudhui ya HTML ambayo itandikwa kwenye ukurasa kwa **`innerHTML`** bila kusafishwa (**XSS**).
Njia ya kupita **kikaguzi cha kwanza** ni kwa kufanya **`window.calc.contentWindow`** kuwa **`undefined`** na **`e.source`** kuwa **`null`**:
- **`window.calc.contentWindow`** kwa kweli ni **`document.getElementById("calc")`**. Unaweza kuharibu **`document.getElementById`** kwa **`![]()
`** (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).
- Kwa hivyo, unaweza kuharibu **`document.getElementById("calc")`** kwa **`![]()
`**. Kisha, **`window.calc`** itakuwa **`undefined`**.
- 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
```javascript
let iframe = document.createElement("iframe")
document.body.appendChild(iframe)
window.target = window.open("http://localhost:8080/")
await new Promise((r) => setTimeout(r, 2000)) // wait for page to load
iframe.contentWindow.eval(`window.parent.target.postMessage("A", "*")`)
document.body.removeChild(iframe) //e.origin === null
```
Ili kupita **ukaguzi wa pili** kuhusu token ni kwa kutuma **`token`** yenye thamani `null` na kufanya thamani ya **`window.token`** kuwa **`undefined`**:
- Kutuma `token` katika postMessage yenye thamani `null` ni rahisi.
- **`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`**.
Suluhisho la mwisho na [**@terjanq**](https://twitter.com/terjanq) ni [**ifuatayo**](https://gist.github.com/terjanq/0bc49a8ef52b0e896fca1ceb6ca6b00e#file-calc-html):
```html
```
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