CVE-2017-16652

Vulnerability

In Symfony versions 2.7.x before 2.7.38, 2.8.x before 2.8.31, 3.2.x before 3.2.14, and 3.3.x before 3.3.13, the DefaultAuthenticationSuccessHandler and DefaultAuthenticationFailureHandler classes use the _target_path request parameter to build a redirect response after authentication. No validation is performed to ensure the path is relative or belongs to the same domain, so an attacker can supply an absolute URL pointing to an external domain. This flaw is an open redirect vulnerability [1][2].

Exploitation

An attacker needs to craft a login URL that includes a _target_path parameter whose value is an absolute URL to an external site under their control (e.g., https://evil.com/). When a user clicks such a link and completes the Symfony authentication process, the success or failure handler will redirect the user to that external URL. The attacker does not require any special network position or authentication; user interaction (clicking the crafted link and logging in) is sufficient [1][3].

Impact

Successful exploitation allows an attacker to redirect users from a legitimate Symfony application to an arbitrary external domain. This open redirect can be leveraged for phishing campaigns, tricking users into entering credentials or sensitive information on a malicious site that appears to be the legitimate application, thereby compromising confidentiality and trust [1].

Mitigation

Symfony addressed this issue in versions 2.7.38, 2.8.31, 3.2.14, and 3.3.13. Users running affected versions should upgrade immediately to the corresponding patched release. No workaround is described in the available references [4].