I'm using apache 2.4 (on linux) with mod_auth_ntlm_winbind to do authentication in a windows environment. I've noticed that sometimes, the username returned by mod_auth_ntlm_winbind is corrupted, even though the authentication itself succeeds. I've done some debugging and I think I found the cause. In source3/utils/ntlm_auth.c, in the function manage_gensec_request, near line 1681:

...
        } else {
            reply_code = "AF";
            reply_arg = session_info->unix_info->unix_name;
            talloc_free(session_info);
        }
...

    case GSS_SPNEGO_SERVER:
        x_fprintf(x_stdout, "%s %s %s\n", reply_code,
                 out_base64 ? out_base64 : "*",
                 reply_arg ? reply_arg : "*");

I think the problem is that session_info->unix_info->unix_name (via reply_arg) is being used after it's been freed. I've hacked the source on my system to do

char replyArgBuffer[80]; /* somewhere near the beginning of the function */
...
        } else {
            reply_code = "AF";
            strncpy(replyArgBuffer, session_info->unix_info->unix_name, sizeof(replyArgBuffer));
            reply_arg = replyArgBuffer;
            talloc_free(session_info);
        }

and that seems to have fixed the problem.