RealNetworks RealPlayer/HelixPlayer SMIL wallclock Stack Overflow
Vulnerability

iDefense Security Advisory 06.26.07
http://labs.idefense.com/intelligence/vulnerabilities/ 
Jun 26, 2007

I. BACKGROUND

RealPlayer is an application for playing various media formats,
developed by RealNetworks Inc. HelixPlayer is the open source version
of RealPlayer. More information can be found at the URLs shown below.

http://www.real.com/realplayer.html 
http://helixcommunity.org/ 

Synchronized Multimedia Integration Language (SMIL) is a markup language
used to specify the use of several multi-media concepts when rendering
media. Some such concepts are timing, transitions, and embedding. More
information is available from WikiPedia at the following URL.

http://en.wikipedia.org/wiki/Synchronized_Multimedia_Integration_Language 

II. DESCRIPTION

Remote exploitation of a buffer overflow within RealNetworks' RealPlayer
and HelixPlayer allows attackers to execute arbitrary code in the context
of the user.

The issue specifically exists in the handling of HH:mm:ss.f time formats
by the 'wallclock' functionality within the code supporting SMIL2. An
excerpt from the code follows.

   924    HX_RESULT
   925    SmilTimeValue::parseWallClockValue(REF(const char*) pCh)
   926    {
   ...
   957        char buf[10]; /* Flawfinder: ignore */
   ...
   962        while (*pCh)
   963        {
   ...
   972             else if (isspace(*pCh) || *pCh == '+' || *pCh == '-'
|| *pCh == 'Z')
   973             {
   974                 // this will find the last +, - or Z... which is
what we want.
   975                 pTimeZone = pCh;
   976             }
   ...
   982             ++pCh;
   983        }
   ...
  1101        if (pTimePos)
  1102        {
  1103        //HH:MM...
  ....
  1133          if (*(pos-1) == ':')
  1134          {
  ....
  1148            if (*(pos-1) == '.')
  1149            {
  1150            // find end.
  1151            UINT32 len = 0;
  1152            if (pTimeZone)
  1153            {
  1154                len = pTimeZone - pos;
  1155            }
  1156            else
  1157            {
  1158                len = end - pos;
  1159            }
  1160            strncpy(buf, pos, len); /* Flawfinder: ignore */

The stack buffer is declared to be 10 bytes on line 957. You can see
that it has a comment which will cause the FlawFinder program to ignore
this buffer.

The loop, which begins on line 962, runs through the parameter to the
function looking for characters that denote different sections of the
time format. When it encounters white space, or the +, -, or Z
characters it will record the location for later use. If a time was
located and it contains both a colon and a period the vulnerable code
will be reached.

The length of data to copy into the stack buffer is calculated either on
line 1154 or line 1158 depending on whether or not a timezone is present.
Neither calculations take into consideration the constant length of the
'buf' buffer and therefore a stack-based buffer overflow can occur on
line 1160. Again, notice that this unsafe use of strncpy() is also
marked with a FlawFinder ignore comment.

III. ANALYSIS

Exploitation requires that an attacker persuade a user to supply
RealPlayer or HelixPlayer with a maliciously crafted SMIL file. For
example, this can be accomplished by convincing them to visit a
malicious web page.

The data that is used to overflow the buffer is quite limited in the
range of characters that are allowed. However, given the ease of
address space manipulation within web browsers, exploitation is not
substantially impacted by this limitation.

The RealPlayer plug-in can be referenced within a web browser by using
CFCDAA03-8BE4-11cf-B84B-0020AFBBCCFA CLSID.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in version
10.5-GOLD of RealNetworks' RealPlayer and HelixPlayer. Confirmation of
the existence this vulnerability within HelixPlayer was done via source
code review. Older versions are assumed to be vulnerable.

V. WORKAROUND

For Windows systems, setting the kill-bit for the associated CLSID,
despite greatly reducing the media player's functionality, will
mitigate exploitation. It should be noted that the CLSID listed may not
be the only CLSID allowing access to the vulnerable code.

VI. VENDOR RESPONSE

RealNetworks has addressed this vulnerability by releasing fixed
versions of their software.

RealNetworks has not provided iDefense with any links referring to
updated packages or advisories. Installing the latest version from
their web site will address the vulnerability.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2007-3410 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org/), which standardizes names for 
security problems.

VIII. DISCLOSURE TIMELINE

10/02/2006  Initial vendor notification
10/03/2006  Initial vendor response
06/26/2007  Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright =A9 2007 iDefense, Inc.

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Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
 There are no warranties with regard to this information. Neither the
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