---------- Forwarded message ---------- Date: Fri, 23 Jun 2000 09:18:22 -0000 From: Lamagra Argamal To: BUGTRAQ@SECURITYFOCUS.COM Subject: ftpd: the advisory version The story begins inside the ftpcmd.y file. Which has the ftp commands in it. The bug is in the site_exec(char *cmd) function. There is calls lreply(200,cmd); In ftpd.c we find void lreply(int n, char *fmt,...) .... vvreply(USE_REPLY_LONG, n, fmt, ap) ... and void vreply(long flags, int n, char *fmt, va_list ap) ... vvsnprintf(buf + (n ? 4 : 0), n ? sizeof(buf) - 4 : sizeof(buf), fmt, ap) .... cmd becomes fmt with vsnprintf that's bad. The idea is to put in formatstrings to get some extra priviledges. We can use %n to overwrite some stuff. eg. overwrite a ret-address or a null at the end of a buffer (cause an overflow) or change the configuration or uid like I did in my proftp exploit (check proftp_pcc.c on Packetstorm). There are some other bugs in site_exec like for (t = cmd; *t && !isspace(*t); t++) { if (isupper(*t)) { *t = tolower(*t); } } Sanitizing stops at a space?? (good thing I didn't tell you this, eh tf8) Wuftpd is all really buggy code. I prefer proftpd, it has clean, readable code and it's quite secure. I did some checking and found some minor bugs there too First in modules/mod_pam.c /* Allocate our entries...we don't free this because PAM does this for us. */ pam_user = malloc(strlen(cmd->argv[0]) + 1); if(pam_user == (char *)0) return pam_return_type ? ERROR(cmd) : DECLINED(cmd); sstrncpy(pam_user, cmd->argv[0], strlen(cmd->argv[0]) + 1); pam_pass = malloc(strlen(cmd->argv[1]) + 1); Pam doesn't free these according to me. So this could lead to a pottential system DoS if abused. Fortunatly proftpd has a limit of 3 on USER/PASS. Second: In the set_proc_title(char *fmt,...) function in main.c It constructs a buffer with hostname + user + cmd to replace argv[0]. If setproctitle(char *fmt,...) is available (only on debian and bsd). It calls setproctitle(statsbuf); what re-opens the old bug Not a big thing since almost nobody has it. -- Chad Whitten chadwick@intop.net -- To unsubscribe send e-mail to suse-linux-e-unsubscribe@suse.com For additional commands send e-mail to suse-linux-e-help@suse.com Also check the FAQ at http://www.suse.com/Support/Doku/FAQ/