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RealNetworks RealPlayer/HelixPlayer SMIL wallclock Stack Overflow Vulnerability

06.26.07

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

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.

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.

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.

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.

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.

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.

DISCLOSURE TIMELINE

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

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2007 Verisign, 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 customer service for permission.

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 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.