Core Security - Corelabs Advisory
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IcoFX Buffer Overflow Vulnerability


1. *Advisory Information*

Title: IcoFX Buffer Overflow Vulnerability
Advisory ID: CORE-2013-1107
Advisory URL:
http://www.coresecurity.com/advisories/icofx-buffer-overflow-vulnerability
Date published: 2013-12-10
Date of last update: 2013-12-10
Vendors contacted: IcoFX Software
Release mode: User release


2. *Vulnerability Information*

Class: Buffer overflow [CWE-119]
Impact: Code execution
Remotely Exploitable: No
Locally Exploitable: Yes
CVE Name: CVE-2013-4988


3. *Vulnerability Description*

IcoFX [1] is prone to a (client side) security vulnerability when
processing .ICO files. This vulnerability could be exploited by a remote
attacker to execute arbitrary code on the target machine, by enticing
the user of IcoFX to open a specially crafted icon file.


4. *Vulnerable Packages*

   . IcoFX v2.5.0.0 for Windows.
   . Other versions are probably affected too, but they were not checked.


5. *Vendor Information, Solutions and Workarounds*

There was no official answer from vendor after several attempts to
report this vulnerability (see [Sec. 8]). As mitigation action, given
that this is a client-side vulnerability, avoid to open untrusted ICO
files. Contact vendor for further information.


6. *Credits*

This vulnerability was discovered and researched by Marcos Accossatto
from Core Exploit Writers Team. The publication of this advisory was
coordinated by Fernando Miranda from Core Advisories Team.


7. *Technical Description / Proof of Concept Code*

Below is shown the result of opening the maliciously crafted file
'CORE-2013-1107-icofx-poc.ico'[2] on Windows XP SP3 (EN).

The vulnerable function is located in 0x80D9F8. By loading the PoC, the
loop [0x80DA74, 0x80DA93] fills the buffer and overwrite the Exception
Handler:

/-----
0080DA74    8B45 E8           MOV EAX,DWORD PTR SS:[EBP-18]
0080DA77    03C0              ADD EAX,EAX
0080DA79    8D94C5 8CF9FFFF   LEA EDX,DWORD PTR SS:[EBP+EAX*8-674]
0080DA80    B9 10000000       MOV ECX,10                               ;
Will copy 16 bytes from file to buffer
0080DA85    8B45 F8           MOV EAX,DWORD PTR SS:[EBP-8]
0080DA88    8B18              MOV EBX,DWORD PTR DS:[EAX]
0080DA8A    FF53 0C           CALL DWORD PTR DS:[EBX+C]
0080DA8D    FF45 E8           INC DWORD PTR SS:[EBP-18]                ;
Index, will be overwritten with our value in the penultimate loop turn
0080DA90    FF4D DC           DEC DWORD PTR SS:[EBP-24]                ;
Counter, will be overwritten with our value in the penultimate loop turn
0080DA93    75 DF             JNZ SHORT 0080DA74
0080DA95    0FBF45 F0         MOVSX EAX,WORD PTR SS:[EBP-10]
-----/

At the 'MOVSX' of 0x80DA95, the CPU registers are as follows:


/-----
EAX 00000010
ECX 7C80189C kernel32.7C80189C
EDX 00000010
EBX 004617F4 IcoFX2.004617F4
ESP 0012F380
EBP 0012FA08
ESI 005B2CBC IcoFX2.005B2CBC
EDI 02555C80
EIP 0080DA95 IcoFX2.0080DA95
C 1  ES 0023 32bit 0(FFFFFFFF)
P 1  CS 001B 32bit 0(FFFFFFFF)
A 0  SS 0023 32bit 0(FFFFFFFF)
Z 1  DS 0023 32bit 0(FFFFFFFF)
S 0  FS 003B 32bit 7FFDF000(FFF)
T 0  GS 0000 NULL
D 0
O 0  LastErr ERROR_SUCCESS (00000000)
EFL 00200247 (NO,B,E,BE,NS,PE,GE,LE)
ST0 empty -??? FFFF 00F300F3 00F300F3
ST1 empty -??? FFFF 00FE00FE 00FE00FE
ST2 empty -??? FFFF 00000009 00220065
ST3 empty -??? FFFF 0000000A 00240069
ST4 empty 1.2948274137727088000e+16
ST5 empty 2.5896178900861029000e+16
ST6 empty 3.2651492439228483000e+16
ST7 empty 3.1244147623526446000e+16
               3 2 1 0      E S P U O Z D I
FST 0000  Cond 0 0 0 0  Err 0 0 0 0 0 0 0 0  (GT)
FCW 1272  Prec NEAR,53  Mask    1 1 0 0 1 0
-----/

And the stack Exception Handler is overwritten (shellcode starts in
0x12F3A4):


/-----
0012F380   0012FA10  Pointer to next SEH record
0012F384   42424242  SE handler
0012F388   41414141
0012F38C   41414141
0012F390   41414141
0012F394   000502A8
0012F398   7E4188A6  USER32.GetWindowLongW
0012F39C   00000000
0012F3A0   0012F3D8  ASCII "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"...
0012F3A4   41414141
-----/

As a result, the normal execution flow can be altered in order to
execute arbitrary code.


8. *Report Timeline*

. 2013-11-11:
Core Security Technologies attempts to contact the IcoFX team; no reply
received. Publication date is set for Dec 3rd, 2013.

. 2013-11-14:
Core attempts to contact vendor.

. 2013-11-26:
Core attempts to contact vendor.

. 2013-12-03:
Core attempts to contact vendor.

. 2013-12-03:
First release date missed.

. 2013-12-10:
Advisory CORE-2013-1107 published.


9. *References*

[1]  http://icofx.ro/.
[2]
http://www.coresecurity.com/system/files/attachments/2013/12/CORE-2013-1107-icofx-poc.zip


10. *About CoreLabs*

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12. *Disclaimer*

The contents of this advisory are copyright (c) 2013 Core Security
Technologies and (c) 2013 CoreLabs, and are licensed under a Creative
Commons Attribution Non-Commercial Share-Alike 3.0 (United States)
License: http://creativecommons.org/licenses/by-nc-sa/3.0/us/


13. *PGP/GPG Keys*

This advisory has been signed with the GPG key of Core Security
Technologies advisories team, which is available for download at
http://www.coresecurity.com/files/attachments/core_security_advisories.asc.