Here's a detailed description of what's going wrong with [STYLE]@;/*
The problem is the unterminated comment "/*"; IE computes the length of the comment for a memcpy opperation by substracting the end pointer form the start pointer. The comment starts behind "/*" and should end at "*/", but since there is no terminator, the start of the string is used. IE there for calculates the string to be -2 unicode characters long. The subsequent memcpy will try to copy 0xFFFFFFFE bytes untill it gets a read or write exception. (You will see the offending instruction is a REP MOVSD)
Unfortunately for us hackers, I believe you cannot control the length value for the memcpy other then setting it to -2. So you will always cause a read or write exception. You will only overwrite a small part of the heap before the exception is caused so overwriting the SEH to controlling execution is also ruled out.
Conclusion: lame DoS
I did find another way to use this to cause an exception at a different location:
[SCRIPT]
d = window.open().document;
d.write("x");
d.body.innerHTML = "<STYLE>@;/*";
[/SCRIPT]
This will crash because of a null pointer in a CMP [ESI], 0.
It didn't look interesting to me, so no detailed investigation.
Cheers,
SkyLined
----- Original Message -----
From: "Phuong Nguyen" <phuong (at) ecqurity (dot) com [email concealed]>
To: <full-disclosure (at) lists.netsys (dot) com [email concealed]>
Sent: Friday, July 23, 2004 19:17
Subject: [Full-Disclosure] Crash IE with 11 bytes ;)
> Hey,
>
> I thought you guys might want to know that it only takes 11 bytes to crash
> IE 5.x , 6.x SP1. CSS memory corruption vulnerability. All you need to do
> is <style>;@/* ;) simple as that. More details@
> http://www.ecqurity.com/adv/IEstyle.html
>
> Phuong
>
>
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.netsys.com/full-disclosure-charter.html
The problem is the unterminated comment "/*"; IE computes the length of the comment for a memcpy opperation by substracting the end pointer form the start pointer. The comment starts behind "/*" and should end at "*/", but since there is no terminator, the start of the string is used. IE there for calculates the string to be -2 unicode characters long. The subsequent memcpy will try to copy 0xFFFFFFFE bytes untill it gets a read or write exception. (You will see the offending instruction is a REP MOVSD)
Unfortunately for us hackers, I believe you cannot control the length value for the memcpy other then setting it to -2. So you will always cause a read or write exception. You will only overwrite a small part of the heap before the exception is caused so overwriting the SEH to controlling execution is also ruled out.
Conclusion: lame DoS
I did find another way to use this to cause an exception at a different location:
[SCRIPT]
d = window.open().document;
d.write("x");
d.body.innerHTML = "<STYLE>@;/*";
[/SCRIPT]
This will crash because of a null pointer in a CMP [ESI], 0.
It didn't look interesting to me, so no detailed investigation.
Cheers,
SkyLined
----- Original Message -----
From: "Phuong Nguyen" <phuong (at) ecqurity (dot) com [email concealed]>
To: <full-disclosure (at) lists.netsys (dot) com [email concealed]>
Sent: Friday, July 23, 2004 19:17
Subject: [Full-Disclosure] Crash IE with 11 bytes ;)
> Hey,
>
> I thought you guys might want to know that it only takes 11 bytes to crash
> IE 5.x , 6.x SP1. CSS memory corruption vulnerability. All you need to do
> is <style>;@/* ;) simple as that. More details@
> http://www.ecqurity.com/adv/IEstyle.html
>
> Phuong
>
>
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.netsys.com/full-disclosure-charter.html
[ reply ]