Executive brief
phpBB, a popular open-source forum software, is vulnerable to a flaw that allows attackers to manipulate password reset emails. By tricking the system into using a malicious web address, an attacker can send a legitimate-looking password reset link to a user that actually directs them to a site controlled by the attacker. If a user clicks this link, the attacker can capture their credentials and take over their account.
Technical details
phpBB before 3.3.16 and version 4.0.0-a1 are vulnerable to Host Header Injection (CWE-640). When the 'force_server_vars' configuration is disabled, the application may use the HTTP Host header provided by the client to generate absolute URLs for password reset emails. An attacker can provide a malicious Host header during a password reset request; if the web server does not validate this header, the resulting email will contain a reset link pointing to an attacker-controlled domain. This allows the attacker to intercept the reset token when the victim clicks the link, leading to account takeover. The issue is patched in versions 3.3.16 and 4.0.0-a2.
Affected products
- phpBB phpBB >= 3.0.0, < 3.3.16; 4.0.0-a1
Timeline
- 2026-04-27: patched: Patch released in version 4.0.0-a2
- 2026-05-04: disclosed
- 2026-05-04: advisory