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X41 D-Sec GmbH Security Advisory: X41-2018-007

Multiple Vulnerabilities in mgetty
==================================


Overview
- --------
Confirmed Affected Versions: 1.2.0
Patched Versions: 1.2.1
Vendor: mgetty
Vendor URL: http://mgetty.greenie.net
Credit: X41 D-Sec GmbH, Eric Sesterhenn
Status: Public
Advisory-URL: https://www.x41-dsec.de/lab/advisories/x41-2018-007-mgetty


Summary and Impact
- ------------------
Multiple issues have been identified in the mgetty fax software. These
might be used by local users to elevate their privileges.
X41 did not perform a full test or audit on the software.


Product Description
- -------------------
- From the vendor: For those of you that do not know mgetty+sendfax yet:
it's a reliable and proven fax send and receive solution for unix and
Linux. But it can do much more... so read the docs and be surprised.

Shell injection via faxq-helper
===============================
Severity Rating: Medium
Vector: Fax Job
CVE: CVE-2018-16741
CWE: 78
CVSS Score: 6.1
CVSS Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:H/A:N
In fax/faxq-helper.c function do_activate(), not all characters are
properly sanitized to prevent command injection. It is possible to use
||, && or > to change the control flow.

{% highlight c %}
        /* replace all quote characters, backslash and ';' by '' */
        for( q = buf; *q != '\0'; q++ )
        {
            if ( *q == '\'' || *q == '"' || *q == '`' ||
                 *q == '\' || *q == ';' )
                                    { *q = ''; }
        }
{% endhighlight %}

A job file containing malicious input can be constructed using
faxq-helper activate <jobid>. One faxrunq is started, the code is
executed as the user running the command.

{% highlight bash %}
        /* replace all quote characters, backslash and ';' by '' */
    #               "   '    \    $   ;
    command=tr -d '\042\047\140\134\044\073' <JOB | \
             $AWK 'BEGIN { phone="-"; flags=""; pages="" }
                  $1=="phone" { phone=$2 }
                  $1=="header"     { flags=flags" -h "$2 }
                  $1=="poll"       { flags=flags" -p" }
                  $1=="normalres" { flags=flags" -n" }
                  $1=="accthandle" { flags=flags" -A
\""substr($0,13)"\"" }
                  $1=="pages" { for( i=2; i<=NF; i++) pages=pages$i" " }
                  END { printf "'"$FAXSENDER"' -v%s %s %s", \
                               flags, phone, pages }' -`


execute faxsend command
=======================
$echo "$command"

eval $command
{% endhighlight %}


Stack Based Buffer Overflow With Long Username in
contrib/next-login/login.c
============================================================================
Severity Rating: Low
Vector: Command Line Parameter
CVE: CVE-2018-16743
CWE: 121
CVSS Score: 2.9
CVSS Vector: CVSS:3.0/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
In file contrib/next-login/login.c the command line parameter username
is passed unsanitized to strcpy(), which causes a stack based buffer
overflow if too long.

{% highlight c %}
        char tbuf[MAXPATHLEN + 2], tname[sizeof(PATHTTY) + 10];
...
        if (*argv) {
                username = *argv;
                ask = 0;
...
                if (failures && strcmp(tbuf, username)) {
                        if (failures > (pwd ? 0 : 1))
                                badlogin(tbuf);
                        failures = 0;
                }
                (void)strcpy(tbuf, username);
{% endhighlight %}


Stack Based Buffer Overflow With Long Argument in contrib/scrts.c
=================================================================
Severity Rating: Low
Vector: Command Line Parameter
CVE: CVE-2018-16742
CWE: 121
CVSS Score: 2.9
CVSS Vector: CVSS:3.0/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
In file contrib/scrts.c a stack buffer overflow can be triggered via
command line parameter.

{% highlight c %}
int main( int argc, char ** argv )
{
int i, fd;
struct termios tio;
char device[1000];

for ( i=1; i<argc; i++ )

{

    if ( strchr( argv[i], '/' ) == NULL )

        sprintf( device, "/dev/%s", argv[i] );

    else

        strcpy( device, argv[i] );
{% endhighlight %}


Stack Based Buffer Overflow and Command injection in faxrec.c
=============================================================
Severity Rating: Low
Vector: Command Line Parameter
CVE: CVE-2018-16744 (for command injection), CVE-2018-16745 (for overflow)
CWE: 121
CVSS Score: 2.9
CVSS Vector: CVSS:3.0/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
In file faxrec.c function fax_notify_mail(), the mail_to parameter is
not sanitized. It could allow for command injection or a buffer
overflow if it is too long. If is called from facrec() which in turn
is called from main() in mgetty.c. Since the notify_mail parameter is
a configuration parameter, it should only be possible to set it from
trusted source. If mgetty would be used with e.g. a webfront end, this
might be abused for a privilege escalation.

{% highlight c %}
void faxnotifymail P3( (pagenum, ppagenum, mailto),
                          int pagenum, int ppagenum, char * mailto )
{
FILE  * pipefp;
char  * filename, * p;
char    buf[256];
int     r;
timet  ti;
    lprintf( LNOISE, "faxnotifymail: sending mail to: %s", mailto );
    sprintf( buf, "%s %s >/dev/null 2>&1", MAILER, mailto );
    pipefp = popen( buf, "w" );
{% endhighlight %}


Endless loop in g3/g32pbm.c
===========================
When converting g32 files using g3/g32pbm.c, an endless loop can be
triggered by malformed input file. Example can be found at
files/g32pmbinfiniteloop.

Out Of Bounds Access in g3/pbm2g3.c
===================================
When converting pbm files using g3/pbm2g3.c, out of bounds accesses
can occur with malformed input files in putwhitespan(). An example can
be found with files/pbm2g2oobaccess.

{% highlight c %}
     putcode( twhite[l].bitcode, twhite[l].bitlength );
{% endhighlight %}


Workaround
- ----------
None.


Timeline
- --------
2018-06-07 Issues found
2018-08-27 Issue reported to vendor
2018-08-28 Vendor reply
2018-09-08 Vendors sends patches
2018-09-08 CVE IDs requested
2018-09-09 CVE IDs assigned
2018-09-11 Patched Version released
2018-09-11 Advisory released

About X41 D-SEC GmbH
====================
X41 is an expert provider for application security services.
Having extensive industry experience and expertise in the area of
information security, a strong core security team of world class
security experts enables X41 to perform premium security services.
Fields of expertise in the area of application security are security
centered code reviews, binary reverse engineering and vulnerability
discovery.
Custom research and a IT security consulting and support services are
core competencies of X41.

- -- 
X41 D-SEC GmbH, Dennewartstr. 25-27, D-52068 Aachen
T: +49 241 9809418-0, Fax: -9
Unternehmenssitz: Aachen, Amtsgericht Aachen: HRB19989
GeschA$?ftsfA1/4hrer: Markus Vervier


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