ApostropheCMS is an open-source Node.js content management system. Versions up to and including 4.29.0 have a password reset flow that constructs the reset URL using `req.hostname`, which is derived directly from the attacker-controlled HTTP `Host` header when `apos.baseUrl` is not explicitly configured. An unauthenticated attacker who knows a victim's email address can send a crafted reset request that causes the application to email the victim a reset link pointing to the attacker's domain. When the victim clicks the link, the valid reset token is delivered to the attacker, enabling full account takeover. As of time of publication, no known patched versions are available.

Affected: npm: apostrophe

## Summary

ApostropheCMS's password reset flow constructs the reset URL using `req.hostname`, which is derived directly from the attacker-controlled HTTP `Host` header when `apos.baseUrl` is not explicitly configured. An unauthenticated attacker who knows a victim's email address can send a crafted reset request that causes the application to email the victim a reset link pointing to the attacker's domain. When the victim clicks the link, the valid reset token is delivered to the attacker, enabling full account takeover.

## Affected Component

`modules/@apostrophecms/login/index.js` — `resetRequest` route Precondition: `passwordReset: true` is set **and** `apos.baseUrl` is not configured.

## Vulnerability Details

The `setPrefixUrls` middleware (i18n layer) builds `req.baseUrl` using `req.hostname`:

```js // Simplified from i18n middleware req.baseUrl = `${req.protocol}://${req.hostname}`; req.absoluteUrl = req.baseUrl + req.url; ```

The `resetRequest` handler then passes this tainted value directly into URL construction:

```js const parsed = new URL( req.absoluteUrl, // ← tainted by attacker's Host header self.apos.baseUrl ? undefined : `${req.protocol}://${req.hostname}${port}` // ← also tainted ); parsed.pathname = '/login'; parsed.searchParams.append('reset', reset); // real, valid token parsed.searchParams.append('email', user.email); await self.email(..., { url: parsed.toString() }, ...); // Email sent to victim with URL pointing…