[UNIX] Sendmail Memory Leak DoS

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Sendmail Memory Leak DoS
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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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