Apple’s basicConstraints vulnerability in Apple’s iOS certificate validation has been revealed. We developed a proof-of-concept app* that implements a better workaround, with some help from OpenSSL. Requests to any site with an invalid certificate chain will fail if they try to exploit the flaw. The code we released contains a fully-functional test app, which demonstrates how to use OpenSSL to double-check the results of Apple’s security framework (i.e. from a SecTrustEvaluate function call) to augment the default certificate validation mechanism.”]
Source: https://duo.com/blog/working-around-phoney-ssl-certificates-on-ios-with-openssl/