# 6.1.16 pwn HITBGSECCTF2017 1000levels - [题目复现](#题目复现) - [题目解析](#题目解析) - [Exploit](#exploit) - [参考资料](#参考资料) [下载文件](../src/writeup/6.1.16_pwn_hitbgsecctf2017_1000levels) ## 题目复现 ``` $ file 1000levels 1000levels: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 2.6.32, BuildID[sha1]=d0381dfa29216ed7d765936155bbaa3f9501283a, not stripped $ checksec -f 1000levels RELRO STACK CANARY NX PIE RPATH RUNPATH FORTIFY Fortified Fortifiable FILE Partial RELRO No canary found NX enabled PIE enabled No RPATH No RUNPATH No 0 6 1000levels $ strings libc.so.6 | grep "GNU C" GNU C Library (Ubuntu GLIBC 2.23-0ubuntu9) stable release version 2.23, by Roland McGrath et al. Compiled by GNU CC version 5.4.0 20160609. ``` 关闭了 Canary，开启 NX 和 PIE。于是猜测可能是栈溢出，但需要绕过 ASLR。not stripped 可以说是很开心了。 玩一下： ``` $ ./1000levels Welcome to 1000levels, it's much more diffcult than before. 1. Go 2. Hint 3. Give up Choice: 1 How many levels? 0 Coward Any more? 1 Let's go!' ==================================================== Level 1 Question: 0 * 0 = ? Answer:0 Great job! You finished 1 levels in 1 seconds ``` Go 的功能看起来就是让你先输入一个数，然后再输入一个数，两个数相加作为 levels，然后让你做算术。 但是很奇怪的是，如果你使用了 Hint 功能，然后第一个数输入了 0 的时候，无论第二个数是多少，仿佛都会出现无限多的 levels： ``` $ ./1000levels Welcome to 1000levels, it's much more diffcult than before. 1. Go 2. Hint 3. Give up Choice: 2 NO PWN NO FUN 1. Go 2. Hint 3. Give up Choice: 1 How many levels? 0 Coward Any more? 1 More levels than before! Let's go!' ==================================================== Level 1 Question: 0 * 0 = ? Answer:0 ==================================================== Level 2 Question: 1 * 1 = ? Answer:1 ==================================================== Level 3 Question: 1 * 1 = ? Answer:1 ==================================================== Level 4 Question: 3 * 1 = ? Answer: ``` 所以应该重点关注一下 Hint 功能。 ## 题目解析 程序比较简单，基本上只有 Go 和 Hint 两个功能。 #### go ``` [0x000009d0]> pdf @ sym.go / (fcn) sym.go 372 | sym.go (); | ; var int local_120h @ rbp-0x120 | ; var int local_118h @ rbp-0x118 | ; var int local_114h @ rbp-0x114 | ; var int local_110h @ rbp-0x110 | ; var int local_108h @ rbp-0x108 | ; CALL XREF from 0x00000f9f (main) | 0x00000b7c push rbp | 0x00000b7d mov rbp, rsp | 0x00000b80 sub rsp, 0x120 | 0x00000b87 lea rdi, str.How_many_levels ; 0x1094 ; "How many levels?" | 0x00000b8e call sym.imp.puts ; int puts(const char *s) | 0x00000b93 call sym.read_num ; ssize_t read(int fildes, void *buf, size_t nbyte) | 0x00000b98 mov qword [local_120h], rax ; 将第一个数放进 local_120h | 0x00000b9f mov rax, qword [local_120h] | 0x00000ba6 test rax, rax | ,=< 0x00000ba9 jg 0xbb9 | | 0x00000bab lea rdi, str.Coward ; 0x10a5 ; "Coward" | | 0x00000bb2 call sym.imp.puts ; int puts(const char *s) | ,==< 0x00000bb7 jmp 0xbc7 | || ; JMP XREF from 0x00000ba9 (sym.go) | |`-> 0x00000bb9 mov rax, qword [local_120h] | | 0x00000bc0 mov qword [local_110h], rax | | ; JMP XREF from 0x00000bb7 (sym.go) | `--> 0x00000bc7 lea rdi, str.Any_more ; 0x10ac ; "Any more?" | 0x00000bce call sym.imp.puts ; int puts(const char *s) | 0x00000bd3 call sym.read_num ; ssize_t read(int fildes, void *buf, size_t nbyte) | 0x00000bd8 mov qword [local_120h], rax | 0x00000bdf mov rdx, qword [local_110h] | 0x00000be6 mov rax, qword [local_120h] | 0x00000bed add rax, rdx ; '(' | 0x00000bf0 mov qword [local_110h], rax | 0x00000bf7 mov rax, qword [local_110h] | 0x00000bfe test rax, rax | ,=< 0x00000c01 jg 0xc14 | | 0x00000c03 lea rdi, str.Coward ; 0x10a5 ; "Coward" | | 0x00000c0a call sym.imp.puts ; int puts(const char *s) | ,==< 0x00000c0f jmp 0xcee | |`-> 0x00000c14 mov rax, qword [local_110h] | | 0x00000c1b cmp rax, 0x3e7 | |,=< 0x00000c21 jle 0xc3c | || 0x00000c23 lea rdi, str.More_levels_than_before ; 0x10b6 ; "More levels than before!" | || 0x00000c2a call sym.imp.puts ; int puts(const char *s) | || 0x00000c2f mov qword [local_108h], 0x3e8 | ,===< 0x00000c3a jmp 0xc4a | ||| ; JMP XREF from 0x00000c21 (sym.go) | ||`-> 0x00000c3c mov rax, qword [local_110h] | || 0x00000c43 mov qword [local_108h], rax | || ; JMP XREF from 0x00000c3a (sym.go) | `---> 0x00000c4a lea rdi, str.Let_s_go ; 0x10cf ; "Let's go!'" | | 0x00000c51 call sym.imp.puts ; int puts(const char *s) | | 0x00000c56 mov edi, 0 | | 0x00000c5b call sym.imp.time ; time_t time(time_t *timer) | | 0x00000c60 mov dword [local_118h], eax | | 0x00000c66 mov rax, qword [local_108h] | | 0x00000c6d mov edi, eax | | 0x00000c6f call sym.level_int ; 进入计算题游戏 | | 0x00000c74 test eax, eax | | 0x00000c76 setne al | | 0x00000c79 test al, al | |,=< 0x00000c7b je 0xcd8 | || 0x00000c7d mov edi, 0 | || 0x00000c82 call sym.imp.time ; time_t time(time_t *timer) | || 0x00000c87 mov dword [local_114h], eax | || 0x00000c8d mov edx, dword [local_114h] | || 0x00000c93 mov eax, dword [local_118h] | || 0x00000c99 sub edx, eax | || 0x00000c9b mov rax, qword [local_108h] | || 0x00000ca2 lea rcx, [local_120h] | || 0x00000ca9 lea rdi, [rcx + 0x20] ; "@" | || 0x00000cad mov ecx, edx | || 0x00000caf mov rdx, rax | || 0x00000cb2 lea rsi, str.Great_job__You_finished__d_levels_in__d_seconds ; 0x10e0 ; "Great job! You finished %d levels in %d seconds\n" | || 0x00000cb9 mov eax, 0 | || 0x00000cbe call sym.imp.sprintf ; int sprintf(char *s, | || 0x00000cc3 lea rax, [local_120h] | || 0x00000cca add rax, 0x20 | || 0x00000cce mov rdi, rax | || 0x00000cd1 call sym.imp.puts ; int puts(const char *s) | ,===< 0x00000cd6 jmp 0xce4 | ||| ; JMP XREF from 0x00000c7b (sym.go) | ||`-> 0x00000cd8 lea rdi, str.You_failed. ; 0x1111 ; "You failed." | || 0x00000cdf call sym.imp.puts ; int puts(const char *s) | || ; JMP XREF from 0x00000cd6 (sym.go) | `---> 0x00000ce4 mov edi, 0 | | 0x00000ce9 call sym.imp.exit ; void exit(int status) | | ; JMP XREF from 0x00000c0f (sym.go) | `--> 0x00000cee leave \ 0x00000cef ret ``` 计算题游戏的函数 `sym.level_int()` 如下： ``` [0x000009d0]> pdf @ sym.level_int / (fcn) sym.level_int 289 | sym.level_int (); | ; var int local_34h @ rbp-0x34 | ; var int local_30h @ rbp-0x30 | ; var int local_28h @ rbp-0x28 | ; var int local_20h @ rbp-0x20 | ; var int local_18h @ rbp-0x18 | ; var int local_10h @ rbp-0x10 | ; var int local_ch @ rbp-0xc | ; var int local_8h @ rbp-0x8 | ; var int local_4h @ rbp-0x4 | ; CALL XREF from 0x00000c6f (sym.go) | ; CALL XREF from 0x00000e70 (sym.level_int) | 0x00000e2d push rbp | 0x00000e2e mov rbp, rsp | 0x00000e31 sub rsp, 0x40 ; '@' | 0x00000e35 mov dword [local_34h], edi | 0x00000e38 mov qword [local_30h], 0 | 0x00000e40 mov qword [local_28h], 0 | 0x00000e48 mov qword [local_20h], 0 | 0x00000e50 mov qword [local_18h], 0 | 0x00000e58 cmp dword [local_34h], 0 | ,=< 0x00000e5c jne 0xe68 | | 0x00000e5e mov eax, 1 | ,==< 0x00000e63 jmp 0xf4c | || ; JMP XREF from 0x00000e5c (sym.level_int) | |`-> 0x00000e68 mov eax, dword [local_34h] | | 0x00000e6b sub eax, 1 | | 0x00000e6e mov edi, eax | | 0x00000e70 call sym.level_int | | 0x00000e75 test eax, eax | | 0x00000e77 sete al | | 0x00000e7a test al, al | |,=< 0x00000e7c je 0xe88 | || 0x00000e7e mov eax, 0 | ,===< 0x00000e83 jmp 0xf4c | ||| ; JMP XREF from 0x00000e7c (sym.level_int) | ||`-> 0x00000e88 call sym.imp.rand ; int rand(void) | || 0x00000e8d cdq | || 0x00000e8e idiv dword [local_34h] | || 0x00000e91 mov dword [local_8h], edx | || 0x00000e94 call sym.imp.rand ; int rand(void) | || 0x00000e99 cdq | || 0x00000e9a idiv dword [local_34h] | || 0x00000e9d mov dword [local_ch], edx | || 0x00000ea0 mov eax, dword [local_8h] | || 0x00000ea3 imul eax, dword [local_ch] | || 0x00000ea7 mov dword [local_10h], eax | || 0x00000eaa lea rdi, str. ; 0x1160 ; "====================================================" | || 0x00000eb1 call sym.imp.puts ; int puts(const char *s) | || 0x00000eb6 mov eax, dword [local_34h] | || 0x00000eb9 mov esi, eax | || 0x00000ebb lea rdi, str.Level__d ; 0x1195 ; "Level %d\n" | || 0x00000ec2 mov eax, 0 | || 0x00000ec7 call sym.imp.printf ; int printf(const char *format) | || 0x00000ecc mov edx, dword [local_ch] | || 0x00000ecf mov eax, dword [local_8h] | || 0x00000ed2 mov esi, eax | || 0x00000ed4 lea rdi, str.Question:__d____d_____Answer: ; 0x119f ; "Question: %d * %d = ? Answer:" | || 0x00000edb mov eax, 0 | || 0x00000ee0 call sym.imp.printf ; int printf(const char *format) | || 0x00000ee5 lea rax, [local_30h] | || 0x00000ee9 mov edx, 0x400 | || 0x00000eee mov rsi, rax | || 0x00000ef1 mov edi, 0 | || 0x00000ef6 call sym.imp.read ; ssize_t read(int fildes, void *buf, size_t nbyte) | || 0x00000efb mov dword [local_4h], eax | || ; JMP XREF from 0x00000f16 (sym.level_int) | ||.-> 0x00000efe mov eax, dword [local_4h] | ||: 0x00000f01 and eax, 7 | ||: 0x00000f04 test eax, eax | ,====< 0x00000f06 je 0xf18 | |||: 0x00000f08 mov eax, dword [local_4h] | |||: 0x00000f0b cdqe | |||: 0x00000f0d mov byte [rbp + rax - 0x30], 0 | |||: 0x00000f12 add dword [local_4h], 1 | |||`=< 0x00000f16 jmp 0xefe | ||| ; JMP XREF from 0x00000f06 (sym.level_int) | `----> 0x00000f18 lea rax, [local_30h] | || 0x00000f1c mov edx, 0xa | || 0x00000f21 mov esi, 0 | || 0x00000f26 mov rdi, rax | || 0x00000f29 call sym.imp.strtol ; long strtol(const char *str, char**endptr, int base) | || 0x00000f2e mov rdx, rax | || 0x00000f31 mov eax, dword [local_10h] | || 0x00000f34 cdqe | || 0x00000f36 cmp rdx, rax | || 0x00000f39 sete al | || 0x00000f3c test al, al | ||,=< 0x00000f3e je 0xf47 | ||| 0x00000f40 mov eax, 1 | ,====< 0x00000f45 jmp 0xf4c | |||| ; JMP XREF from 0x00000f3e (sym.level_int) | |||`-> 0x00000f47 mov eax, 0 | ||| ; JMP XREF from 0x00000f45 (sym.level_int) | ||| ; JMP XREF from 0x00000e83 (sym.level_int) | ||| ; JMP XREF from 0x00000e63 (sym.level_int) | ```--> 0x00000f4c leave \ 0x00000f4d ret ``` #### hint ``` [0x000009d0]> pdf @ sym.hint / (fcn) sym.hint 140 | sym.hint (); | ; var int local_110h @ rbp-0x110 | ; CALL XREF from 0x00000fa6 (main) | 0x00000cf0 push rbp | 0x00000cf1 mov rbp, rsp | 0x00000cf4 sub rsp, 0x110 | 0x00000cfb mov rax, qword [reloc.system] ; [0x201fd0:8]=0 | 0x00000d02 mov qword [local_110h], rax | 0x00000d09 lea rax, obj.show_hint ; 0x20208c | 0x00000d10 mov eax, dword [rax] | 0x00000d12 test eax, eax | ,=< 0x00000d14 je 0xd41 | | 0x00000d16 mov rax, qword [local_110h] | | 0x00000d1d lea rdx, [local_110h] | | 0x00000d24 lea rcx, [rdx + 8] | | 0x00000d28 mov rdx, rax | | 0x00000d2b lea rsi, str.Hint:__p ; 0x111d ; "Hint: %p\n" | | 0x00000d32 mov rdi, rcx | | 0x00000d35 mov eax, 0 | | 0x00000d3a call sym.imp.sprintf ; int sprintf(char *s, | ,==< 0x00000d3f jmp 0xd66 | || ; JMP XREF from 0x00000d14 (sym.hint) | |`-> 0x00000d41 lea rax, [local_110h] | | 0x00000d48 add rax, 8 | | 0x00000d4c movabs rsi, 0x4e204e5750204f4e | | 0x00000d56 mov qword [rax], rsi | | 0x00000d59 mov dword [rax + 8], 0x5546204f ; [0x5546204f:4]=-1 | | 0x00000d60 mov word [rax + 0xc], 0x4e ; 'N' ; [0x4e:2]=0 | | ; JMP XREF from 0x00000d3f (sym.hint) | `--> 0x00000d66 lea rax, [local_110h] | 0x00000d6d add rax, 8 | 0x00000d71 mov rdi, rax | 0x00000d74 call sym.imp.puts ; int puts(const char *s) | 0x00000d79 nop | 0x00000d7a leave \ 0x00000d7b ret ``` ## Exploit ## 参考资料 - https://ctftime.org/task/4539