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
IcoFX  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.
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.
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.
Below is shown the result of opening the maliciously crafted file
CORE-2013-1107-icofx-poc.ico 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]
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.
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