diff --git a/doc/6.2.5_re_picoctf2014_baleful.md b/doc/6.2.5_re_picoctf2014_baleful.md index f5a8d7f..60e4862 100644 --- a/doc/6.2.5_re_picoctf2014_baleful.md +++ b/doc/6.2.5_re_picoctf2014_baleful.md @@ -1,6 +1,8 @@ # 6.2.5 re PicoCTF2014 Baleful - [题目解析](#题目解析) + - [逆向 VM 求解](#逆向-vm-求解) + - [使用 Pin 求解](#使用-pin-求解) - [参考资料](#参考资料) @@ -17,23 +19,298 @@ $Id: UPX 3.91 Copyright (C) 1996-2013 the UPX Team. All Rights Reserved. $ UPX!u UPX! UPX! -$ upx -d baleful -o baleful_de +$ upx -d baleful -o baleful_unpack Ultimate Packer for eXecutables Copyright (C) 1996 - 2017 UPX 3.94 Markus Oberhumer, Laszlo Molnar & John Reiser May 12th 2017 File size Ratio Format Name -------------------- ------ ----------- ----------- - 144956 <- 6752 4.66% linux/i386 baleful_de + 144956 <- 6752 4.66% linux/i386 baleful_unpack Unpacked 1 file. -$ file baleful_de -baleful_de: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=35d1a373cbe6a675ecbbc904722a86f853f20ce3, stripped +$ file baleful_unpack +baleful_unpack: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, for GNU/Linux 2.6.24, BuildID[sha1]=35d1a373cbe6a675ecbbc904722a86f853f20ce3, stripped ``` +经过简单地检查，我们发现二进制文件被加了壳，使用 upx 脱掉就好了。 + +运行下看看，典型的密码验证题： ``` -$ ./baleful_de +$ ./baleful_unpack Please enter your password: ABCD Sorry, wrong password! ``` +#### 逆向 VM 求解 +打开 r2 开干吧！ +``` +[0x08048540]> pdf @ main +/ (fcn) main 96 +| main (); +| ; var int local_8h @ ebp-0x8 +| ; var int local_10h @ esp+0x10 +| ; var int local_8ch @ esp+0x8c +| ; DATA XREF from 0x08048557 (entry0) +| 0x08049c82 55 push ebp +| 0x08049c83 89e5 mov ebp, esp +| 0x08049c85 57 push edi +| 0x08049c86 53 push ebx +| 0x08049c87 83e4f0 and esp, 0xfffffff0 +| 0x08049c8a 81ec90000000 sub esp, 0x90 +| 0x08049c90 65a114000000 mov eax, dword gs:[0x14] ; [0x14:4]=-1 ; 20 +| 0x08049c96 8984248c0000. mov dword [local_8ch], eax +| 0x08049c9d 31c0 xor eax, eax +| 0x08049c9f 8d442410 lea eax, [local_10h] ; 0x10 ; 16 +| 0x08049ca3 89c3 mov ebx, eax +| 0x08049ca5 b800000000 mov eax, 0 +| 0x08049caa ba1f000000 mov edx, 0x1f ; 31 +| 0x08049caf 89df mov edi, ebx +| 0x08049cb1 89d1 mov ecx, edx +| 0x08049cb3 f3ab rep stosd dword es:[edi], eax +| 0x08049cb5 8d442410 lea eax, [local_10h] ; 0x10 ; 16 +| 0x08049cb9 890424 mov dword [esp], eax +| 0x08049cbc e8caecffff call fcn.0804898b +| 0x08049cc1 b800000000 mov eax, 0 +| 0x08049cc6 8b94248c0000. mov edx, dword [local_8ch] ; [0x8c:4]=-1 ; 140 +| 0x08049ccd 653315140000. xor edx, dword gs:[0x14] +| ,=< 0x08049cd4 7405 je 0x8049cdb +| | 0x08049cd6 e8e5e7ffff call sym.imp.__stack_chk_fail ; void __stack_chk_fail(void) +| | ; JMP XREF from 0x08049cd4 (main) +| `-> 0x08049cdb 8d65f8 lea esp, [local_8h] +| 0x08049cde 5b pop ebx +| 0x08049cdf 5f pop edi +| 0x08049ce0 5d pop ebp +\ 0x08049ce1 c3 ret +``` + +`fcn.0804898b` 是程序主要的逻辑所在，很容易看出来它其实是实现了一个虚拟机： +``` +[0x08048540]> pdf @ fcn.0804898b +Linear size differs too much from the bbsum, please use pdr instead. +[0x08048540]> pdr @ fcn.0804898b +/ (fcn) fcn.0804898b 226 +| fcn.0804898b (int arg_8h); +| ; var int local_b4h @ ebp-0xb4 +| ; var int local_38h @ ebp-0x38 +| ; var int local_34h @ ebp-0x34 +| ; var int local_30h @ ebp-0x30 +| ; var int local_2ch @ ebp-0x2c +| ; var int local_28h @ ebp-0x28 +| ; var int local_24h @ ebp-0x24 +| ; var int local_20h @ ebp-0x20 +| ; var int local_1ch @ ebp-0x1c +| ; var int local_18h @ ebp-0x18 +| ; var int local_14h @ ebp-0x14 +| ; var int local_10h @ ebp-0x10 +| ; var int local_ch @ ebp-0xc +| ; arg int arg_8h @ ebp+0x8 +| ; CALL XREF from 0x08049cbc (main) +| 0x0804898b 55 push ebp +| 0x0804898c 89e5 mov ebp, esp +| 0x0804898e 81ecc8000000 sub esp, 0xc8 +| 0x08048994 c745cc001000. mov dword [local_34h], 0x1000 +| 0x0804899b 837d0800 cmp dword [arg_8h], 0 +| 0x0804899f 742a je 0x80489cb +| ----------- true: 0x080489cb false: 0x080489a1 +| 0x080489a1 c745d0000000. mov dword [local_30h], 0 +| 0x080489a8 eb19 jmp 0x80489c3 +| ----------- true: 0x080489c3 +| ; JMP XREF from 0x080489c7 (fcn.0804898b) +| 0x080489aa 8b45d0 mov eax, dword [local_30h] +| 0x080489ad c1e002 shl eax, 2 +| 0x080489b0 034508 add eax, dword [arg_8h] +| 0x080489b3 8b10 mov edx, dword [eax] +| 0x080489b5 8b45d0 mov eax, dword [local_30h] +| 0x080489b8 8994854cffff. mov dword [ebp + eax*4 - 0xb4], edx +| 0x080489bf 8345d001 add dword [local_30h], 1 +| ----------- true: 0x080489c3 +| ; JMP XREF from 0x080489a8 (fcn.0804898b) +| 0x080489c3 837dd01e cmp dword [local_30h], 0x1e ; [0x1e:4]=-1 ; 30 +| 0x080489c7 7ee1 jle 0x80489aa +| ----------- true: 0x080489aa false: 0x080489c9 +| 0x080489c9 eb21 jmp 0x80489ec +| ----------- true: 0x080489ec +| ; JMP XREF from 0x0804899f (fcn.0804898b) +| 0x080489cb c745d4000000. mov dword [local_2ch], 0 +| 0x080489d2 eb12 jmp 0x80489e6 +| ----------- true: 0x080489e6 +| ; JMP XREF from 0x080489ea (fcn.0804898b) +| 0x080489d4 8b45d4 mov eax, dword [local_2ch] +| 0x080489d7 c784854cffff. mov dword [ebp + eax*4 - 0xb4], 0 +| 0x080489e2 8345d401 add dword [local_2ch], 1 +| ----------- true: 0x080489e6 +| ; JMP XREF from 0x080489d2 (fcn.0804898b) +| 0x080489e6 837dd41e cmp dword [local_2ch], 0x1e ; [0x1e:4]=-1 ; 30 +| 0x080489ea 7ee8 jle 0x80489d4 +| ----------- true: 0x080489d4 false: 0x080489ec +| ; JMP XREF from 0x080489c9 (fcn.0804898b) +| 0x080489ec c745c800f000. mov dword [local_38h], 0xf000 +| 0x080489f3 c745d8000000. mov dword [local_28h], 0 +| 0x080489fa c745ec000000. mov dword [local_14h], 0 +| 0x08048a01 c745f0000000. mov dword [local_10h], 0 +| 0x08048a08 c745f4000000. mov dword [local_ch], 0 +| 0x08048a0f c745e8000000. mov dword [local_18h], 0 +| 0x08048a16 8b45e8 mov eax, dword [local_18h] +| 0x08048a19 8945e4 mov dword [local_1ch], eax +| 0x08048a1c 8b45e4 mov eax, dword [local_1ch] +| 0x08048a1f 8945e0 mov dword [local_20h], eax +| 0x08048a22 8b45e0 mov eax, dword [local_20h] +| 0x08048a25 8945dc mov dword [local_24h], eax +| 0x08048a28 e93a120000 jmp 0x8049c67 +| ----------- true: 0x08049c67 +| ; JMP XREF from 0x08049c74 (fcn.0804898b) +| 0x08048a2d 8b45cc mov eax, dword [local_34h] +| 0x08048a30 05c0c00408 add eax, 0x804c0c0 +| 0x08048a35 0fb600 movzx eax, byte [eax] +| 0x08048a38 0fbec0 movsx eax, al +| 0x08048a3b 83f820 cmp eax, 0x20 ; 32 +| 0x08048a3e 0f871e120000 ja 0x8049c62 +| ----------- true: 0x08049c62 false: 0x08048a44 +| 0x08048a44 8b0485d49d04. mov eax, dword [eax*4 + 0x8049dd4] ; [0x8049dd4:4]=0x8048a4d +| 0x08048a4b ffe0 jmp eax + +| ; JMP XREF from 0x08048a3e (fcn.0804898b) +| 0x08049c62 8345cc01 add dword [local_34h], 1 +| 0x08049c66 90 nop +| ----------- true: 0x08049c67 +| ; XREFS: JMP 0x08048a28 JMP 0x08048a51 JMP 0x08048a8a JMP 0x08048bbf JMP 0x08048cf4 JMP 0x08048e2a JMP 0x08048f8c JMP 0x080490c1 +| ; XREFS: JMP 0x080491f6 JMP 0x0804932b JMP 0x08049462 JMP 0x08049599 JMP 0x080495f0 JMP 0x08049644 JMP 0x08049698 JMP 0x080496cc +| ; XREFS: JMP 0x080496e7 JMP 0x08049710 JMP 0x08049739 JMP 0x08049762 JMP 0x0804978b JMP 0x080497b4 JMP 0x080497dd JMP 0x080498eb +| ; XREFS: JMP 0x080499fd JMP 0x08049a81 JMP 0x08049ab4 JMP 0x08049ae7 JMP 0x08049b3e JMP 0x08049b8d JMP 0x08049bf6 JMP 0x08049c2c +| ; XREFS: JMP 0x08049c60 +| 0x08049c67 8b45cc mov eax, dword [local_34h] +| 0x08049c6a 05c0c00408 add eax, 0x804c0c0 +| 0x08049c6f 0fb600 movzx eax, byte [eax] +| 0x08049c72 3c1d cmp al, 0x1d ; 29 +| 0x08049c74 0f85b3edffff jne 0x8048a2d +| ----------- true: 0x08048a2d false: 0x08049c7a +| 0x08049c7a 8b854cffffff mov eax, dword [local_b4h] +| ; JMP XREF from 0x08048a6f (fcn.0804898b + 228) +| 0x08049c80 c9 leave +\ 0x08049c81 c3 ret +``` + +``` +[0x08048540]> px @ 0x0804c060 +- offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF +0x0804c060 7c86 0408 ad86 0408 d486 0408 a987 0408 |............... +0x0804c070 fb86 0408 1b87 0408 4e87 0408 d887 0408 ........N....... +0x0804c080 1986 0408 1388 0408 3488 0408 7b88 0408 ........4...{... +0x0804c090 b688 0408 f188 0408 2c89 0408 6086 0408 ........,...`... +0x0804c0a0 6a86 0408 6789 0408 0000 0000 0000 0000 j...g........... +``` + + +#### 使用 Pin 求解 +就像上面那样逆向实在是太难了，不如 Pin 的黑科技。 + +编译 32 位 pintool： +``` +[ManualExamples]$ make obj-ia32/inscount0.so TARGET= +``` +随便输入几个长度不同的密码试试： +``` +[ManualExamples]$ echo "A" | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack ; cat inscount.out +Please enter your password: Sorry, wrong password! +Count 437603 +[ManualExamples]$ echo "AA" | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack ; cat inscount.out +Please enter your password: Sorry, wrong password! +Count 438397 +[ManualExamples]$ echo "AAA" | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack ; cat inscount.out +Please enter your password: Sorry, wrong password! +Count 439191 +``` +``` +$ python -c 'print(439191 - 438397)' +794 +$ python -c 'print(438397 - 437603)' +794 +``` +指令执行的次数呈递增趋势，完美，这样只要递增到这个次数有不同时，就可以得到正确的密码长度： +```python +import os + +def get_count(flag): + cmd = "echo " + "\"" + flag + "\"" + " | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack" + os.system(cmd) + with open("inscount.out") as f: + count = int(f.read().split(" ")[1]) + return count + +flag = "A" +p_count = get_count(flag) +for i in range(50): + flag += "A" + count = get_count(flag) + print("count: ", count) + diff = count - p_count + print("diff: ", diff) + if diff != 794: + break + p_count = count +print("length of password: ", len(flag)) +``` +``` +Please enter your password: Sorry, wrong password! +count: 459041 +diff: 794 +Please enter your password: Sorry, wrong password! +count: 459835 +diff: 794 +Please enter your password: Sorry, wrong password! +count: 508273 +diff: 48438 +length of password: 30 +``` +好，密码长度为 30，接下来是逐字符爆破，首先要确定字符不同对 count 没有影响： +``` +[ManualExamples]$ echo "A" | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack ; cat inscount.out +Please enter your password: Sorry, wrong password! +Count 437603 +[ManualExamples]$ echo "b" | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack ; cat inscount.out +Please enter your password: Sorry, wrong password! +Count 437603 +[ManualExamples]$ echo "_" | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack ; cat inscount.out +Please enter your password: Sorry, wrong password! +Count 437603 +``` +确实没有，写下脚本： +```python +import os + +def get_count(flag): + cmd = "echo " + "\"" + flag + "\"" + " | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack" + os.system(cmd) + with open("inscount.out") as f: + count = int(f.read().split(" ")[1]) + return count + +charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-+*'" + +flag = list("A" * 30) +p_count = get_count("".join(flag)) +for i in range(30): + for c in charset: + flag[i] = c + print("".join(flag)) + count = get_count("".join(flag)) + print("count: ", count) + if count != p_count: + break + p_count = count +print("password: ", "".join(flag)) +``` +``` +packers_and_vms_and_xors_oh_mx +Please enter your password: Sorry, wrong password! +count: 507925 +packers_and_vms_and_xors_oh_my +Please enter your password: Congratulations! +count: 505068 +password: packers_and_vms_and_xors_oh_my +``` +简单到想哭。 + + ## 参考资料 +- [Pico CTF 2014 : Baleful](https://github.com/ctfs/write-ups-2014/tree/master/pico-ctf-2014/master-challenge/baleful-200) diff --git a/src/writeup/6.2.5_re_picoctf2014_baleful/baleful_de b/src/writeup/6.2.5_re_picoctf2014_baleful/baleful_unpack similarity index 100% rename from src/writeup/6.2.5_re_picoctf2014_baleful/baleful_de rename to src/writeup/6.2.5_re_picoctf2014_baleful/baleful_unpack diff --git a/src/writeup/6.2.5_re_picoctf2014_baleful/exp_pin.py b/src/writeup/6.2.5_re_picoctf2014_baleful/exp_pin.py new file mode 100644 index 0000000..119d14a --- /dev/null +++ b/src/writeup/6.2.5_re_picoctf2014_baleful/exp_pin.py @@ -0,0 +1,23 @@ +import os + +def get_count(flag): + cmd = "echo " + "\"" + flag + "\"" + " | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack" + os.system(cmd) + with open("inscount.out") as f: + count = int(f.read().split(" ")[1]) + return count + +charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_-+*'" + +flag = list("A" * 30) +p_count = get_count("".join(flag)) +for i in range(30): + for c in charset: + flag[i] = c + print("".join(flag)) + count = get_count("".join(flag)) + print("count: ", count) + if count != p_count: + break + p_count = count +print("password: ", "".join(flag)) diff --git a/src/writeup/6.2.5_re_picoctf2014_baleful/exp_pin_len.py b/src/writeup/6.2.5_re_picoctf2014_baleful/exp_pin_len.py new file mode 100644 index 0000000..44fa73c --- /dev/null +++ b/src/writeup/6.2.5_re_picoctf2014_baleful/exp_pin_len.py @@ -0,0 +1,21 @@ +import os + +def get_count(flag): + cmd = "echo " + "\"" + flag + "\"" + " | ../../../pin -t obj-ia32/inscount0.so -o inscount.out -- ~/baleful_unpack" + os.system(cmd) + with open("inscount.out") as f: + count = int(f.read().split(" ")[1]) + return count + +flag = "A" +p_count = get_count(flag) +for i in range(50): + flag += "A" + count = get_count(flag) + print("count: ", count) + diff = count - p_count + print("diff: ", diff) + if diff != 794: + break + p_count = count +print("length of password: ", len(flag))