> > > > Program received signal SIGSEGV, Segmentation fault.
> > > > 0x00000000 in ?? ()
> > > > (gdb) bt
> > > > #0 0x00000000 in ?? ()
> > > > #1 0x00432a4d in mdb_node_search (mc=mc@entry=0x289608,
> > > > key=key@entry=0x289850, exactp=exactp@entry=0x289604) at mdb.c:4943
> > > > #2 0x004361bc in mdb_cursor_set (mc=mc@entry=0x289608,
> > > > key=key@entry=0x289850, data=data@entry=0x289858, op=op@entry=MDB_SET,
> > > > exactp=exactp@entry=0x289604) at mdb.c:5725
> > > > #3 0x0043667c in mdb_get (txn=0x35c7b0, dbi=1, key=0x289850, data=0x289858)
> > > > at mdb.c:5391
> > > > #4 0x00431a55 in _sasldb_getdata ()
> > > > #5 0x0042fda3 in sasldb_auxprop_lookup ()
> > > > #6 0x004119f7 in _sasl_auxprop_lookup ()
> > > > #7 0x00413a6c in _sasl_canon_user_lookup ()
> > > > #8 0x0042ea7e in srp_server_mech_step ()
> > > > #9 0x0040cddd in sasl_server_step ()
> > > > #10 0x0040d361 in sasl_server_start ()
> > > > #11 0x0040458f in doauth ()
> > > > #12 0x004060d6 in test_clientfirst ()
> > > > #13 0x00406405 in foreach_mechanism ()
> > > > #14 0x00733d1f in main ()
> > > > (gdb)

> Using Cyrus-SASL 2.1.26 and LMDB 0.9.17 on Linux, I don't see any such problem
> - it fails at GSSAPI because I have no kerberos creds.

Linux you say? You are a lucky man indeed!
On Windows, it segfaults right after the first mechanism.