The best tool for finding one gadget RCE in libc.so.6
When playing ctf pwn challenges we usually need the one-gadget RCE (remote code execution),
which leads to call execve('/bin/sh', NULL, NULL).
This gem provides such gadgets finder, no need to use objdump or IDA-pro every time like a fool 
To use this tool, type one_gadget /path/to/libc in command line and enjoy the magic 
Available on RubyGems.org!
$ gem install one_gadget
Note: requires ruby version >= 2.1.0, you can use ruby --version to check.
OneGadget uses symbolic execution to find the constraints of gadgets to be successful.
The article introducing how I develop this tool can be found on my blog.
$ one_gadget# Usage: one_gadget <FILE|-b BuildID> [options]# -b, --build-id BuildID BuildID[sha1] of libc.# -f, --[no-]force-file Force search gadgets in file instead of build id first.# -l, --level OUTPUT_LEVEL The output level.# OneGadget automatically selects gadgets with higher successful probability.# Increase this level to ask OneGadget show more gadgets it found.# Default: 0# -n, --near FUNCTIONS/FILE Order gadgets by their distance to the given functions or to the GOT functions of the given file.# -o, --output-format FORMAT Output format. FORMAT should be one of <pretty|raw|json>.# Default: pretty# -r, --raw Alias of -o raw. Output gadgets offset only, split with one space.# -s, --script exploit-script Run exploit script with all possible gadgets.# The script will be run as 'exploit-script $offset'.# --info BuildID Show version information given BuildID.# --base BASE_ADDRESS The base address of libc.# Default: 0# --version Current gem version.
$ one_gadget /lib/x86_64-linux-gnu/libc.so.6# 0xe3afe execve("/bin/sh", r15, r12)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3b01 execve("/bin/sh", r15, rdx)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## 0xe3b04 execve("/bin/sh", rsi, rdx)# constraints:# [rsi] == NULL || rsi == NULL || rsi is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp
$ one_gadget -b aad7dbe330f23ea00ca63daf793b766b51aceb5d# 0x4557a execve("/bin/sh", rsp+0x30, environ)# constraints:# [rsp+0x30] == NULL || {[rsp+0x30], [rsp+0x38], [rsp+0x40], [rsp+0x48], ...} is a valid argv## 0xf1651 execve("/bin/sh", rsp+0x40, environ)# constraints:# [rsp+0x40] == NULL || {[rsp+0x40], [rsp+0x48], [rsp+0x50], [rsp+0x58], ...} is a valid argv## 0xf24cb execve("/bin/sh", rsp+0x60, environ)# constraints:# [rsp+0x60] == NULL || {[rsp+0x60], [rsp+0x68], [rsp+0x70], [rsp+0x78], ...} is a valid argv
Consider this scenario when exploiting:
In this scenario you can choose to write two low-byte on a GOT entry with one-gadget’s two low-byte.
If the function offset on GOT is close enough with the one-gadget,
you will have at least 1/16 chance of success.
Reorder gadgets according to the distance of given functions.
$ one_gadget /lib/x86_64-linux-gnu/libc.so.6 --near exit,mkdir# [OneGadget] Gadgets near exit(0x46a40):# 0xe3afe execve("/bin/sh", r15, r12)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3b01 execve("/bin/sh", r15, rdx)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## 0xe3b04 execve("/bin/sh", rsi, rdx)# constraints:# [rsi] == NULL || rsi == NULL || rsi is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## [OneGadget] Gadgets near mkdir(0x10de70):# 0xe3b04 execve("/bin/sh", rsi, rdx)# constraints:# [rsi] == NULL || rsi == NULL || rsi is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## 0xe3b01 execve("/bin/sh", r15, rdx)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## 0xe3afe execve("/bin/sh", r15, r12)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp#
Regular expression is acceptable.
$ one_gadget /lib/x86_64-linux-gnu/libc.so.6 --near 'write.*' --raw# [OneGadget] Gadgets near writev(0x114690):# 932612 932609 932606## [OneGadget] Gadgets near write(0x10e280):# 932612 932609 932606#
Pass an ELF file as the argument, OneGadget will take all GOT functions for processing.
$ one_gadget /lib/x86_64-linux-gnu/libc.so.6 --near spec/data/test_near_file.elf --raw# [OneGadget] Gadgets near exit(0x46a40):# 932606 932609 932612## [OneGadget] Gadgets near puts(0x84420):# 932606 932609 932612## [OneGadget] Gadgets near printf(0x61c90):# 932606 932609 932612## [OneGadget] Gadgets near strlen(0x9f630):# 932606 932609 932612## [OneGadget] Gadgets near __cxa_finalize(0x46f10):# 932606 932609 932612## [OneGadget] Gadgets near __libc_start_main(0x23f90):# 932606 932609 932612#
Sometimes one_gadget finds too many gadgets to show them in one screen,
by default gadgets would be filtered automatically according to the difficulty of constraints.
Use option --level 1 to show all gadgets found instead of only those with higher probabilities.
$ one_gadget /lib/x86_64-linux-gnu/libc.so.6 --level 1# 0x51dfb posix_spawn(rsp+0xc, "/bin/sh", 0, rbp, rsp+0x50, environ)# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# {"sh", "-c", rbx, NULL} is a valid argv# rbp == NULL || (u16)[rbp] == NULL## 0x51e02 posix_spawn(rsp+0xc, "/bin/sh", 0, rbp, rsp+0x50, environ)# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# rax == NULL || {"sh", rax, rbx, NULL} is a valid argv# rbp == NULL || (u16)[rbp] == NULL## 0x51e09 posix_spawn(rsp+0xc, "/bin/sh", 0, rbp, rsp+0x50, environ)# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# rcx == NULL || {rcx, rax, rbx, NULL} is a valid argv# rbp == NULL || (u16)[rbp] == NULL## 0x51e10 posix_spawn(rsp+0xc, "/bin/sh", rdx, rbp, rsp+0x50, environ)# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# rcx == NULL || {rcx, (u64)xmm1, rbx, NULL} is a valid argv# rdx == NULL || (s32)[rdx+0x4] <= 0# rbp == NULL || (u16)[rbp] == NULL## 0x51e15 posix_spawn(rsp+0xc, "/bin/sh", rdx, rbp, rsp+0x50, environ)# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# (u64)xmm0 == NULL || {(u64)xmm0, (u64)xmm1, rbx, NULL} is a valid argv# rdx == NULL || (s32)[rdx+0x4] <= 0# rbp == NULL || (u16)[rbp] == NULL## 0x51e25 posix_spawn(rdi, "/bin/sh", rdx, rbp, rsp+0x50, [rax])# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# (u64)xmm0 == NULL || {(u64)xmm0, (u64)(xmm0 >> 64), rbx, NULL} is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rdi == NULL || writable: rdi# rdx == NULL || (s32)[rdx+0x4] <= 0# rbp == NULL || (u16)[rbp] == NULL## 0x51e2a posix_spawn(rdi, "/bin/sh", rdx, rbp, r8, [rax])# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# [r8] == NULL || r8 is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rdi == NULL || writable: rdi# rdx == NULL || (s32)[rdx+0x4] <= 0# rbp == NULL || (u16)[rbp] == NULL## 0x51e2d posix_spawn(rdi, "/bin/sh", rdx, rcx, r8, [rax])# constraints:# address rsp+0x60 is writable# rsp & 0xf == 0# [r8] == NULL || r8 is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rdi == NULL || writable: rdi# rdx == NULL || (s32)[rdx+0x4] <= 0# rcx == NULL || (u16)[rcx] == NULL## 0x51e32 posix_spawn(rdi, "/bin/sh", rdx, rcx, r8, [rax])# constraints:# address rsp+0x68 is writable# rsp & 0xf == 0# [r8] == NULL || r8 is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rdi == NULL || writable: rdi# rdx == NULL || (s32)[rdx+0x4] <= 0# rcx == NULL || (u16)[rcx] == NULL## 0x84135 posix_spawn(rbx+0xe0, "/bin/sh", r12, 0, rsp+0x60, environ)# constraints:# address rsp+0x70 is writable# rsp & 0xf == 0# {"sh", "-c", rbp, NULL} is a valid argv# rbx+0xe0 == NULL || writable: rbx+0xe0# r12 == NULL || (s32)[r12+0x4] <= 0## 0x8413c posix_spawn(rbx+0xe0, "/bin/sh", r12, 0, rsp+0x60, environ)# constraints:# address rsp+0x70 is writable# rsp & 0xf == 0# rax == NULL || {"sh", rax, rbp, NULL} is a valid argv# rbx+0xe0 == NULL || writable: rbx+0xe0# r12 == NULL || (s32)[r12+0x4] <= 0## 0x84143 posix_spawn(rbx+0xe0, "/bin/sh", r12, 0, rsp+0x60, environ)# constraints:# address rsp+0x70 is writable# rsp & 0xf == 0# rcx == NULL || {rcx, rax, rbp, NULL} is a valid argv# rbx+0xe0 == NULL || writable: rbx+0xe0# r12 == NULL || (s32)[r12+0x4] <= 0## 0x84146 posix_spawn(rbx+0xe0, "/bin/sh", rdx, 0, rsp+0x60, environ)# constraints:# address rsp+0x70 is writable# rsp & 0xf == 0# rcx == NULL || {rcx, rax, rbp, NULL} is a valid argv# rbx+0xe0 == NULL || writable: rbx+0xe0# rdx == NULL || (s32)[rdx+0x4] <= 0## 0x8414b posix_spawn(rbx+0xe0, "/bin/sh", rdx, 0, rsp+0x60, environ)# constraints:# address rsp+0x78 is writable# rsp & 0xf == 0# rcx == NULL || {rcx, rax, [rsp+0x70], NULL} is a valid argv# rbx+0xe0 == NULL || writable: rbx+0xe0# rdx == NULL || (s32)[rdx+0x4] <= 0## 0x84150 posix_spawn(rbx+0xe0, "/bin/sh", rdx, 0, rsp+0x60, environ)# constraints:# address rsp+0x78 is writable# rsp & 0xf == 0# rcx == NULL || {rcx, (u64)xmm1, [rsp+0x70], NULL} is a valid argv# rbx+0xe0 == NULL || writable: rbx+0xe0# rdx == NULL || (s32)[rdx+0x4] <= 0## 0x8415c posix_spawn(rbx+0xe0, "/bin/sh", rdx, 0, rsp+0x60, [rax])# constraints:# address rsp+0x78 is writable# rsp & 0xf == 0# (u64)xmm0 == NULL || {(u64)xmm0, (u64)xmm1, [rsp+0x70], NULL} is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rbx+0xe0 == NULL || writable: rbx+0xe0# rdx == NULL || (s32)[rdx+0x4] <= 0## 0x84162 posix_spawn(rbx+0xe0, "/bin/sh", rdx, rcx, rsp+0x60, [rax])# constraints:# address rsp+0x78 is writable# rsp & 0xf == 0# (u64)xmm0 == NULL || {(u64)xmm0, (u64)(xmm0 >> 64), [rsp+0x70], NULL} is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rbx+0xe0 == NULL || writable: rbx+0xe0# rdx == NULL || (s32)[rdx+0x4] <= 0# rcx == NULL || (u16)[rcx] == NULL## 0x84169 posix_spawn(rdi, "/bin/sh", rdx, rcx, rsp+0x60, [rax])# constraints:# address rsp+0x78 is writable# rsp & 0xf == 0# (u64)xmm0 == NULL || {(u64)xmm0, (u64)(xmm0 >> 64), [rsp+0x70], NULL} is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rdi == NULL || writable: rdi# rdx == NULL || (s32)[rdx+0x4] <= 0# rcx == NULL || (u16)[rcx] == NULL## 0x84170 posix_spawn(rdi, "/bin/sh", rdx, rcx, r8, [rax])# constraints:# address rsp+0x78 is writable# rsp & 0xf == 0# [r8] == NULL || r8 is a valid argv# [[rax]] == NULL || [rax] == NULL || [rax] is a valid envp# rdi == NULL || writable: rdi# rdx == NULL || (s32)[rdx+0x4] <= 0# rcx == NULL || (u16)[rcx] == NULL## 0xe3afe execve("/bin/sh", r15, r12)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3b01 execve("/bin/sh", r15, rdx)# constraints:# [r15] == NULL || r15 == NULL || r15 is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## 0xe3b04 execve("/bin/sh", rsi, rdx)# constraints:# [rsi] == NULL || rsi == NULL || rsi is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## 0xe3cf3 execve("/bin/sh", r10, r12)# constraints:# address rbp-0x78 is writable# [r10] == NULL || r10 == NULL || r10 is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3cf6 execve("/bin/sh", r10, rdx)# constraints:# address rbp-0x78 is writable# [r10] == NULL || r10 == NULL || r10 is a valid argv# [rdx] == NULL || rdx == NULL || rdx is a valid envp## 0xe3d62 execve("/bin/sh", rbp-0x50, r12)# constraints:# address rbp-0x48 is writable# r13 == NULL || {"/bin/sh", r13, NULL} is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3d69 execve("/bin/sh", rbp-0x50, r12)# constraints:# address rbp-0x48 is writable# rax == NULL || {rax, r13, NULL} is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3d70 execve("/bin/sh", rbp-0x50, r12)# constraints:# address rbp-0x50 is writable# rax == NULL || {rax, [rbp-0x48], NULL} is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3da7 execve("/bin/sh", rbp-0x50, r12)# constraints:# address rbp-0x50 is writable# [rbp-0x68] == NULL || {"/bin/sh", [rbp-0x68], NULL} is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3db1 execve("/bin/sh", rbp-0x50, r12)# constraints:# address rbp-0x50 is writable# rax == NULL || {rax, [rbp-0x68], NULL} is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3db5 execve("/bin/sh", r10, r12)# constraints:# addresses r10+0x10, rbp-0x50 are writable# [r10] == NULL || r10 == NULL || r10 is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0xe3dbd execve("/bin/sh", r10, r12)# constraints:# addresses r10+0x10, rbp-0x48 are writable# [r10] == NULL || r10 == NULL || r10 is a valid argv# [r12] == NULL || r12 == NULL || r12 is a valid envp## 0x1077ca posix_spawn(rsp+0x64, "/bin/sh", [rsp+0x38], 0, rsp+0x70, [rsp+0xf0])# constraints:# [rsp+0x70] == NULL || {[rsp+0x70], [rsp+0x78], [rsp+0x80], [rsp+0x88], ...} is a valid argv# [[rsp+0xf0]] == NULL || [rsp+0xf0] == NULL || [rsp+0xf0] is a valid envp# [rsp+0x38] == NULL || (s32)[[rsp+0x38]+0x4] <= 0## 0x1077d2 posix_spawn(rsp+0x64, "/bin/sh", [rsp+0x38], 0, rsp+0x70, r9)# constraints:# [rsp+0x70] == NULL || {[rsp+0x70], [rsp+0x78], [rsp+0x80], [rsp+0x88], ...} is a valid argv# [r9] == NULL || r9 == NULL || r9 is a valid envp# [rsp+0x38] == NULL || (s32)[[rsp+0x38]+0x4] <= 0## 0x1077d7 posix_spawn(rsp+0x64, "/bin/sh", rdx, 0, rsp+0x70, r9)# constraints:# [rsp+0x70] == NULL || {[rsp+0x70], [rsp+0x78], [rsp+0x80], [rsp+0x88], ...} is a valid argv# [r9] == NULL || r9 == NULL || r9 is a valid envp# rdx == NULL || (s32)[rdx+0x4] <= 0## 0x1077e1 posix_spawn(rdi, "/bin/sh", rdx, 0, r8, r9)# constraints:# [r8] == NULL || r8 is a valid argv# [r9] == NULL || r9 == NULL || r9 is a valid envp# rdi == NULL || writable: rdi# rdx == NULL || (s32)[rdx+0x4] <= 0
$ one_gadget /lib32/libc.so.6# 0xc890b execve("/bin/sh", [ebp-0x2c], esi)# constraints:# address ebp-0x20 is writable# ebx is the GOT address of libc# [[ebp-0x2c]] == NULL || [ebp-0x2c] == NULL || [ebp-0x2c] is a valid argv# [esi] == NULL || esi == NULL || esi is a valid envp## 0x1421b3 execl("/bin/sh", eax)# constraints:# ebp is the GOT address of libc# eax == NULL## 0x1421b4 execl("/bin/sh", [esp])# constraints:# ebp is the GOT address of libc# [esp] == NULL
$ one_gadget spec/data/aarch64-libc-2.27.so# 0x3f160 execve("/bin/sh", sp+0x70, environ)# constraints:# address x20+0x338 is writable# x3 == NULL## 0x3f184 execve("/bin/sh", sp+0x70, environ)# constraints:# addresses x19+0x4, x20+0x338 are writable# [sp+0x70] == NULL## 0x3f1a8 execve("/bin/sh", x21, environ)# constraints:# addresses x19+0x4, x20+0x338 are writable# [x21] == NULL || x21 == NULL## 0x63e90 execl("/bin/sh", x1)# constraints:# x1 == NULL
Pass your exploit script as one_gadget‘s arguments, it can
try all gadgets one by one, so you don’t need to try every possible gadgets manually.
$ one_gadget ./spec/data/libc-2.19.so -s 'echo "offset ->"'
require 'one_gadget'OneGadget.gadgets(file: '/lib/x86_64-linux-gnu/libc.so.6')#=> [932606, 932609, 932612]# or in shorter wayone_gadget('/lib/x86_64-linux-gnu/libc.so.6', level: 1)#=> [335355, 335362, 335369, 335376, 335381, 335397, 335402, 335405, 335410, 540981, 540988, 540995, 540998, 541003, 541008, 541020, 541026, 541033, 541040, 932606, 932609, 932612, 933107, 933110, 933218, 933225, 933232, 933287, 933297, 933301, 933309, 1079242, 1079250, 1079255, 1079265]# from build idone_gadget('b417c0ba7cc5cf06d1d1bed6652cedb9253c60d0')#=> [324286, 324293, 324386, 1090444]
import subprocessdef one_gadget(filename):return [int(i) for i in subprocess.check_output(['one_gadget', '--raw', filename]).decode().split(' ')]one_gadget('/lib/x86_64-linux-gnu/libc.so.6')#=> [932606, 932609, 932612]
Any suggestion or feature request is welcome! Feel free to send a pull request.
Please let me know if you find any libc that make OneGadget fail to find gadgets.
And, if you like this work, I’ll be happy to be starred 