[UNIX] Sendmail Memory Leak DoS

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  Sendmail Memory Leak DoS
------------------------------------------------------------------------


SUMMARY

 <http://www.sendmail.com/> sendmail is "a powerful, efficient, and 
scalable Mail Transport Agent"

A memory leak in Sendmail allows attackers to DoS sendmail by exhausting 
memory.

DETAILS

Vulnerable Systems:
 * Sendmail version 8.13.5 and prior
 * Sendmail version 8.12.10 and prior

Immune Systems:
 * Sendmail version 8.13.6

The function sm_syslog at conf.c contain a memory leak.
The memory leak will cause with every  be a usage of sm_syslog, allocation 
of new memory that will never be released, until all available memory has 
been exhausted.

Code Snips:
File conf.c line 5324:
/* VARARGS3 */
void
#ifdef __STDC__
sm_syslog(int level, const char *id, const char *fmt, ...)
#else /* __STDC__ */
sm_syslog(level, id, fmt, va_alist)
..
 for (;;)
 {
  int n;

  /* print log message into buf */
  SM_VA_START(ap, fmt);
  n = sm_vsnprintf(buf, bufsize, fmt, ap);
  SM_VA_END(ap);
  SM_ASSERT(n > 0);
  if (n < bufsize)
   break;

  /* String too small, redo with correct size */
  bufsize = n + 1;
  if (buf != buf0)
  {
   sm_free(buf);
   buf = NULL;
  }
  buf = sm_malloc_x(bufsize);
 }

 /* clean up buf after it has been expanded with args */
 newstring = str2prt(buf);
 if ((strlen(newstring) + idlen + 1) < SYSLOG_BUFSIZE)
 {
..
  if (buf == buf0)
   buf = NULL;     <- Memory leak
  errno = save_errno;
  return;
 }

Vendor Status:
The vendor has issued a fix:  <http://www.sendmail.org/8.13.6.html> 
http://www.sendmail.org/8.13.6.html
Patch for Sendmail version 8.13.5 available at:  
<ftp://ftp.sendmail.org/pub/sendmail/8.13.5.p0> 
ftp://ftp.sendmail.org/pub/sendmail/8.13.5.p0
Patch for Sendmail version 8.12.11 available at:  
<ftp://ftp.sendmail.org/pub/sendmail/8.12.11.p0> 
ftp://ftp.sendmail.org/pub/sendmail/8.12.11.p0


ADDITIONAL INFORMATION

The information has been provided by Ido Kanner (SecuriTeam).



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