Permissioned blockchains are networks with identifiable participants. A prominent example is Hyperledger Fabric, that introduces the execute-order-validate architecture. The execution phase enables defining application level trust assumption by setting an endorsement policy, namely a set of rules that define the peers (affiliated with organizations) who provide attestation of transaction correctness. Since the organizations hosting those peers might collude or be compromised, the number of organizations required by the endorsement policy is often increased to reduce susceptibility to attacks. However, doing so impairs the performance of the system and is impractical in networks comprising of a large number of organizations. In this paper we propose an alternative endorsement protocol that hardens the system's security without hindering performance. We provide a quantitative analysis of the suggested technique, and show that by incorporating verified randomness in endorsement policies, attacks that are based on collusion or malicious peers are effectively mitigated with overwhelming probability.