[SC-L] Interesting tidbit in iDefense Security Advisory 06.26.07

[Kenneth Van Wyk]

SC-L












Cheers,

Ken van Wyk
SC-L Moderator


Begin forwarded message:

I'm not quite so sure why this one (below) caught my eye -- we _all_ get tons of product advisories -- but it did. In particular, two things jump out at me: 1) the original author of the defect thought that s/he was doing things correctly in using strncpy (vs. strcpy). 2) the original author had apparently been doing static source analysis using David Wheeler's Flawfinder tool, as we can tell from the comments. Yet, a simple coding mistake was made in calculating the length of a buffer and passing that incorrect length to strncpy. The result was a buffer overrun on the stack, just like the millions that we've all seen. Mind you, the overrun can only be exploited when specific characters are used as input to the loop in the code. Thus, I'm inclined to think that this is an interesting example of a bug that would have been extraordinarily difficult to find using black box testing, even fuzzing. The iDefense team doesn't say how the (anonymous) person who reported it found it, but I for one would be really curious to hear that story. Just some random thoughts this afternoon... Perhaps I'm still getting over the jet lag after returning from the FIRST conference in Seville.

From: iDefense Labs <[EMAIL PROTECTED]>
Date: June 26, 2007 3:53:46 PM EDT


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/


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.

To: [EMAIL PROTECTED], [EMAIL PROTECTED], [EMAIL PROTECTED] Subject: iDefense Security Advisory 06.26.07: RealNetworks RealPlayer/HelixPlayer SMIL wallclock Stack Overflow Vulnerability Synchronized Multimedia Integration Language (SMIL) is a markup language http://en.wikipedia.org/wiki/ Synchronized_Multimedia_Integration_Language

II. DESCRIPTION


of the user.


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        {
   ...

|| *pCh == 'Z')
   973             {

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

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.


'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

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

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


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.

Get paid for vulnerability research
http://labs.idefense.com/methodology/vulnerability/vcp.php

Free tools, research and upcoming events
http://labs.idefense.com/

X. LEGAL NOTICES

Copyright © 2007 iDefense, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDefense. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically,
please e-mail [EMAIL PROTECTED] for permission.

Disclaimer: The information in the advisory is believed to be accurate

 There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct,
indirect, or consequential loss or damage arising from use of, or
reliance on, this information.

Remote exploitation of a buffer overflow within RealNetworks' RealPlayer and HelixPlayer allows attackers to execute arbitrary code in the context The issue specifically exists in the handling of HH:mm:ss.f time formats 972 else if (isspace(*pCh) || *pCh == '+' || *pCh == '-' 974 // this will find the last +, - or Z... which is that it has a comment which will cause the FlawFinder program to ignore 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 the existence this vulnerability within HelixPlayer was done via source mitigate exploitation. It should be noted that the CLSID listed may not The Common Vulnerabilities and Exposures (CVE) project has assigned the at the time of publishing based on currently available information. Use of the information constitutes acceptance for use in an AS IS condition.

smime.p7s
Description: S/MIME cryptographic signature

_______________________________________________
Secure Coding mailing list (SC-L) SC-L@securecoding.org
List information, subscriptions, etc - http://krvw.com/mailman/listinfo/sc-l
List charter available at - http://www.securecoding.org/list/charter.php
SC-L is hosted and moderated by KRvW Associates, LLC (http://www.KRvW.com)
as a free, non-commercial service to the software security community.
_______________________________________________