Proftpd 1.3.5a LATEST 0day Follow-up report (Part 2), Patch released!! 29/11/2015 --- Advanced Information Security Corporation

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                              Date: 22/11/2015
                      Credit: Nicholas Lemonias


             .::PROFTPD  v1.3.5a  HEAP OVERFLOWS ::.


ADVANCED INFORMATION SECURITY CORPORATION

                                                    Keeping Things Simple!

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     `.::.888.      ::          .88888888
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   `'.:::::::::::88888888888.888:::::::::'
         `':::_:' -- '' -'-' `':_::::'`.


 ==================
INTRODUCTION
 ==================
 ProFTPD is Free and open-source software, compatible with Unix-like
 systems and Microsoft Windows (via Cygwin). Along with vsftpd and
 Pure-FTPd, ProFTPD is among the most popular FTP servers in Unix-like
 environments today. Compared to those, which focus e.g. on simplicity,
 speed or security, ProFTPD's primary design goal is to be a highly
 feature rich FTP server, exposing a large amount of configuration
 options to the user
 ====================================================
 Description: During a manual source code audit of ProFTPD latest,
 various security issues were discovered.
 =====================================================


===========================
CODE SNIPPET (PoC 1)
===========================
 ../../mod_sftp/fxp.c:1217-1251


static struct fxp_extpair *fxp_msg_read_extpair(pool *p, unsigned char **buf,
    uint32_t *buflen) {
  uint32_t namelen, datalen;
  unsigned char *name, *data;
  struct fxp_extpair *extpair;
  namelen = sftp_msg_read_int(p, buf, buflen);
  if (*buflen < namelen) {
    (void) pr_log_writefile(sftp_logfd, MOD_SFTP_VERSION,
      "SFTP message format error: unable to read %lu bytes of extpair name "
      "data (buflen = %lu)", (unsigned long) namelen, (unsigned long) *buflen);
    SFTP_DISCONNECT_CONN(SFTP_SSH2_DISCONNECT_BY_APPLICATION, NULL);
  }
  name = palloc(p, namelen + 1);
  memcpy(name, *buf, namelen);
  (*buf) += namelen;
  (*buflen) -= namelen;
  name[namelen] = '\0';
  datalen = sftp_msg_read_int(p, buf, buflen);
  if (datalen > 0) {
    data = sftp_msg_read_data(p, buf, buflen, datalen);
  } else {
    data = NULL;
  }
  extpair = palloc(p, sizeof(struct fxp_extpair));
  extpair->ext_name = (char *) name;
  extpair->ext_datalen = datalen;
  extpair->ext_data = data;
  return extpair;
}

=====================
RATIONALE
=====================


Part of the SFTP handshake involves "extensions", which are key/value
pairs, comprised of strings.  In SSH, strings are encoded for network
transport as a 32-bit length, followed by the bytes.

The mod_sftp module has no manual bounds/length metrics / limitations
when reading SFTP extension key/value data from the network.


  A malicious attacker might attempt to encode large values, and
allocate more memory than is necessary, cause memory exhaustion.



=======================
CONCLUSION
=======================

To avoid undue resource exhaustion by a remote client, mod_sftp should
include a patch on the maximum length of acceptable extension
keys/values, as reported by our earlier Proftpd report.

==============================

REPORT TIMELINE
==============================
22/11/2015  Reported to vendor. (Initial Report)
25/11/2015  Second report to vendor.

29/11/2015  Bug Report / Patch circulation.




 ==============================
 ACKNOWLEDGEMENTS
 ==============================
 PacketStorm Security,
 TEAM TESO, w00w00, Netric, b0iler (eyeonsecurity), wootehfoot,
 badpack3t (SP), Vandal (Vic), s0kket, mantis, Big_Al , ELFQrin, bob
 (dtors),  epic for their ~ legendary mark.



Big Thanks to TJ from Proftpd for the prompt response to the issue,
and excellent cooperation in security
matters.



====================
REFERENCES
====================
[1]  Proftpd. 2015. Proftpd Bug Report , MOD_SFTP Heap Overflow.
[ONLINE] Available at:
http://bugs.proftpd.org/show_bug.cgi?id=4210. [Accessed 29 November 2015].


[2] Lemonias, N. (2015). SecurityFocus - Proftpd Heap Overflow. [ONLINE]
Securityfocus.com.  Available at:
http://www.securityfocus.com/archive/1/536953/30/0/threaded
[Accessed 29 November 2015].