Eduroam offers secure access to the Internet at participating institutions, using authentication via IEEE 802.1X and secure forwarding of authentication data to the authentication server of the user's institution. Due to erroneous configuration manuals and a lack of knowledge on the user side, though, a big share of client devices lack the required root CA certificate to authenticate the Eduroam network, yet still being able to access the network. Moreover, deficient software implementations on client devices prevent users from the secure execution of the authentication process. In this paper, we present an attack that exploits this fact and uses the default behavior of wireless devices in order to capture authentication data. This MITM attack is performed in real-time. It is achieved using a modified version of hostapd, which exploits a compatibility setting of the widely used supplicant software wpa supplicant. It enables an attacker to authenticate users in EAP-TTLS/PAP and in EAP-TTLS/MS-CHAPv2 without the necessity of cracking the user password hash on the fly and thus without inducing suspicious delays. In a practical study with several hundred users we could show that more than half of the tested devices were vulnerable to the attack. Based on the results of the study, we propose countermeasures to prevent the attack and minimize the amount of vulnerable devices.