<p>Cancelable biometric (CB) protection schemes create more secure biometric data to avoid problems caused by traditional biometric templates related to reversibility and non-renewability if they are compromised. The idea is to transform the original template using a transformation function parameterized with a secret key. The resulting template is supposed to be non-invertible so that an attacker cannot recover the original biometric data even if the key is compromised. Despite the advantages provided by these systems, a large proportion remains vulnerable. In this paper, we propose to study the security performance of a well-known transformation-based CB algorithm proposed by Ratha et al. (2007 in its Cartesian version). We show that the security of this algorithm is dependent on the management of the user-key. If this last one is compromised, the whole template is revealed. The attack is done through two main steps: user-key discovery by exploiting the failure of sharing information between multiple transformed templates of the same individual, and original template reconstruction by formulating and solving system constraints. The correctness and practical impacts of our attack are verified using the databases FVC2002, FVC2004, and FVC2006. The experimental results confirm the effectiveness of the proposed attack.</p>