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": // 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: 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 to attacker-controlled domain When "apos.baseUrl" is configured, it is used unconditionally and the attacker's "Host" header is ignored — that path is not vulnerable. Attack Scenario 1. Attacker identifies a valid user email (e.g. from the site's public interface). 2. Attacker sends: POST /api/v1/login/reset-request Host: evil.attacker.com Content-Type: application/json {"email": "victim@example.com"} 3. The application emails the victim: Click here to reset your password: http://evil.attacker.com/login?reset=TOKEN&email=victim@example.com 4. Victim clicks the link; attacker's server captures "TOKEN". 5. Attacker calls the real target's reset endpoint with the captured token and sets a new password — full account takeover. Preconditions - "passwordReset: true" configured in login module options (opt-in) - "apos.baseUrl" is not set (common in development and some production deployments) - Attacker knows or can enumerate a valid account email Impact Full account takeover of any account whose email address is known to the attacker. No authentication or interaction beyond sending a single HTTP request is required from the attacker. The victim need only click a link in a legitimate-looking password reset email from their own site. Remediation Operators (immediate): Always set "apos.baseUrl" in your configuration: // app.js or module configuration modules: { '@apostrophecms/express': { options: { baseUrl: 'https://yourdomain.com' } } } Framework fix (recommended): The "resetRequest" route should refuse to proceed if "apos.baseUrl" is not configured, rather than falling back to the tainted "req.hostname". Example: // In resetRequest handler if (!self.apos.baseUrl) { throw self.apos.error( 'invalid', 'apos.baseUrl must be configured to enable password reset' ); } const parsed = new URL(self.loginUrl(), self.apos.baseUrl); This eliminates the attacker-controlled input entirely from the URL construction path. References - "OWASP: Host Header Injection" (https://owasp.org/www-project-web-security-testing-guide/latest/4-Web_Application_Security_Testing/07-Input_Validation_Testing/17-Testing_for_Host_Header_Injection) - "CWE-640: Weak Password Recovery Mechanism for Forgotten Password" (https://cwe.mitre.org/data/definitions/640.html)