In src/lib/krb5/krb/authdata.c context is NULL and is dereferenced: static krb5_error_code k5_ad_size(krb5_context kcontext, krb5_authdata_context context, krb5_flags flags, size_t *sizep) { int i; krb5_error_code code = 0; *sizep += sizeof(krb5_int32); /* count */ for (i = 0; i < context->n_modules; i++) { The back trace is: #0 0x0045dfcf in k5_ad_size (kcontext=0x8054af8, context=0x0, flags=15, sizep=0xbffff078) at krb5/src/lib/krb5/krb/authdata.c:162 #1 0x0045f7a2 in krb5_authdata_context_size (kcontext=0x8054af8, ptr=0x0, sizep=0xbffff078) at krb5/src/lib/krb5/krb/authdata.c:1131 (line 1067 in your trunk) #2 0x00484310 in krb5_size_opaque (kcontext=0x8054af8, odtype=-1760647364, arg=0x0, sizep=0xbffff078) at krb5/src/lib/krb5/krb/serialize.c:104 (line 105 in your trunk) #3 0x006ed9c3 in kg_ctx_size (kcontext=0x8054af8, arg=0x8053700, sizep=0xbffff0b4) at krb5/src/lib/gssapi/krb5/ser_sctx.c:361