In file \src\plugins\preauth\pkinit\pkinit_crypto_openssl.h I have found constant:

#define DN_BUF_LENĀ  256

So, the size of DN is limited by 256 bytes. It is very small and can be easily overflowed, especially if DN contains utf8-encoded CN/O/OU.
In this case PKINIT failed with error 'stack smashing detected'.

Please, consider to increase DN_BUF_LEN or use dynamic memory allocation for DN buffer.