https://sourceware.org/bugzilla/show_bug.cgi?id=34656
Bug ID: 34656
Summary: Heap-buffer-overflow write in Intel HEX section
loading (`bfd/ihex.c`)
Product: binutils
Version: 2.47
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: binutils
Assignee: unassigned at sourceware dot org
Reporter: hdzhao214 at gmail dot com
Target Milestone: ---
Created attachment 17015
--> https://sourceware.org/bugzilla/attachment.cgi?id=17015&action=edit
The `artifacts.zip` package includes the PoC generation script, the sanitizer
report, the bug report, and the candidate patch
## Vulnerability description
Intel HEX input is scanned once to determine a section size and read again to
populate the allocation. `ihex_read_section` assumes the input is unchanged and
writes each decoded record without checking the remaining capacity. An attacker
able to modify the file between the passes can enlarge a record after the scan,
causing the second pass to decode more data than was allocated.
```c
for (i = 0; i < len; i++)
*p++ = HEX2 (buf + 2 * i);
```
The supplied modifier changes a two-byte data record into a 255-byte record
while the scanner traverses a long newline tail. The second pass writes 765
bytes into a section sized for 512 bytes.
## Version and commit
GNU Binutils 2.47.50, commit `d715260f420066befb2d30ec8f5befcdf7ecfd84`
(2026-09-08).
## Environment
Ubuntu 24.04.4 LTS, x86_64, Linux 6.8.0-136-generic; GCC 13.3.0 and Python
3.12.3. The target was an AddressSanitizer build. The race input occupies
approximately 600 MB.
## Steps to reproduce
1. Install build prerequisites (for example, on Ubuntu):
```sh
sudo apt-get update
sudo apt-get install -y build-essential bison flex texinfo python3 \\
libgmp-dev libmpfr-dev libmpc-dev zlib1g-dev
```
2. Obtain the affected revision and make an AddressSanitizer build:
```sh
export SRC="$PWD/binutils-gdb"
git clone https://sourceware.org/git/binutils-gdb.git "$SRC"
git -C "$SRC" checkout d715260f420066befb2d30ec8f5befcdf7ecfd84
mkdir "$SRC/build-asan" && cd "$SRC/build-asan"
CC=gcc CFLAGS='-O0 -g3 -fsanitize=address -fno-omit-frame-pointer' \\
LDFLAGS='-fsanitize=address' \\
"$SRC/configure" --disable-gdb --disable-gdbserver --disable-sim \\
--disable-gprofng --disable-gold --disable-werror --disable-nls
make -j"$(nproc)" all-binutils
export BUILD="$SRC/build-asan"
```
3. Place `gen_ihex.py` and `race_modifier.py` in a writable directory and
create the initial input:
```sh
export WORK="$PWD/poc-work"
mkdir -p "$WORK"
python3 gen_ihex.py "$WORK/sample.hex" 64 600000000
```
4. Start the reader, alter the already-scanned record, and wait for it:
```sh
ASAN_OPTIONS=detect_leaks=0:abort_on_error=1 \\
"$BUILD/binutils/objdump" -s -I ihex "$WORK/sample.hex" \\
>"$WORK/asan.txt" 2>&1 &
pid=$!
python3 race_modifier.py "$pid" "$WORK/sample.hex"
wait "$pid"
```
## Sanitizer report
The following is the complete, unmodified contents of `sanitizer_report.txt`.
```text
=================================================================
==29231==ERROR: AddressSanitizer: heap-buffer-overflow on address
0x516000000290 at pc 0x5dbaf0c26047 bp 0x7ffe3b7eea20 sp 0x7ffe3b7eea10
WRITE of size 1 at 0x516000000290 thread T0
#0 0x5dbaf0c26046 in ihex_read_section ../../bfd/ihex.c:597
#1 0x5dbaf0c2639d in ihex_get_section_contents ../../bfd/ihex.c:640
#2 0x5dbaf0c1a174 in bfd_get_section_contents ../../bfd/section.c:1615
#3 0x5dbaf0c070f0 in bfd_is_section_compressed_info
../../bfd/compress.c:901
#4 0x5dbaf0c0752f in bfd_is_section_compressed ../../bfd/compress.c:959
#5 0x5dbaf0ab471e in dump_section ../../binutils/objdump.c:5193
#6 0x5dbaf0c19924 in bfd_map_over_sections ../../bfd/section.c:1369
#7 0x5dbaf0ab4f70 in dump_data ../../binutils/objdump.c:5276
#8 0x5dbaf0ab809c in dump_bfd ../../binutils/objdump.c:5908
#9 0x5dbaf0ab8374 in display_object_bfd ../../binutils/objdump.c:5971
#10 0x5dbaf0ab8696 in display_any_bfd ../../binutils/objdump.c:6050
#11 0x5dbaf0ab8706 in display_file ../../binutils/objdump.c:6071
#12 0x5dbaf0aba222 in main ../../binutils/objdump.c:6494
#13 0x704f1ce2a1c9 in __libc_start_call_main
../sysdeps/nptl/libc_start_call_main.h:58
#14 0x704f1ce2a28a in __libc_start_main_impl ../csu/libc-start.c:360
#15 0x5dbaf0a9d374 in _start
(/home/shootduck/hotracer-experiments/0-day/hotracer/pilot/objdump/2026-09-08-2.47.50-d715260/binutils-gdb/build-asan/binutils/objdump+0x143374)
(BuildId: 7b3b22cfe8266150e71d8e259cd00c3996daee41)
0x516000000290 is located 0 bytes after 528-byte region
[0x516000000080,0x516000000290)
allocated by thread T0 here:
#0 0x704f1d2fd9c7 in malloc
../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:69
#1 0x5dbaf0ec2858 in _objalloc_alloc ../../libiberty/objalloc.c:143
#2 0x5dbaf0c0f501 in bfd_alloc ../../bfd/libbfd.c:453
#3 0x5dbaf0c2630b in ihex_get_section_contents ../../bfd/ihex.c:637
#4 0x5dbaf0c1a174 in bfd_get_section_contents ../../bfd/section.c:1615
#5 0x5dbaf0c070f0 in bfd_is_section_compressed_info
../../bfd/compress.c:901
#6 0x5dbaf0c0752f in bfd_is_section_compressed ../../bfd/compress.c:959
#7 0x5dbaf0ab471e in dump_section ../../binutils/objdump.c:5193
#8 0x5dbaf0c19924 in bfd_map_over_sections ../../bfd/section.c:1369
#9 0x5dbaf0ab4f70 in dump_data ../../binutils/objdump.c:5276
#10 0x5dbaf0ab809c in dump_bfd ../../binutils/objdump.c:5908
#11 0x5dbaf0ab8374 in display_object_bfd ../../binutils/objdump.c:5971
#12 0x5dbaf0ab8696 in display_any_bfd ../../binutils/objdump.c:6050
#13 0x5dbaf0ab8706 in display_file ../../binutils/objdump.c:6071
#14 0x5dbaf0aba222 in main ../../binutils/objdump.c:6494
#15 0x704f1ce2a1c9 in __libc_start_call_main
../sysdeps/nptl/libc_start_call_main.h:58
#16 0x704f1ce2a28a in __libc_start_main_impl ../csu/libc-start.c:360
#17 0x5dbaf0a9d374 in _start
(/home/shootduck/hotracer-experiments/0-day/hotracer/pilot/objdump/2026-09-08-2.47.50-d715260/binutils-gdb/build-asan/binutils/objdump+0x143374)
(BuildId: 7b3b22cfe8266150e71d8e259cd00c3996daee41)
SUMMARY: AddressSanitizer: heap-buffer-overflow ../../bfd/ihex.c:597 in
ihex_read_section
Shadow bytes around the buggy address:
0x516000000000: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x516000000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x516000000100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x516000000180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x516000000200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x516000000280: 00 00[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa
0x516000000300: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x516000000380: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x516000000400: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x516000000480: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x516000000500: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
Shadow byte legend (one shadow byte represents 8 application bytes):
Addressable: 00
Partially addressable: 01 02 03 04 05 06 07
Heap left redzone: fa
Freed heap region: fd
Stack left redzone: f1
Stack mid redzone: f2
Stack right redzone: f3
Stack after return: f5
Stack use after scope: f8
Global redzone: f9
Global init order: f6
Poisoned by user: f7
Container overflow: fc
Array cookie: ac
Intra object redzone: bb
ASan internal: fe
Left alloca redzone: ca
Right alloca redzone: cb
==29231==ABORTING
```
## Potential fix
Treat the second pass as parsing untrusted current input: validate record
syntax and reject a record whose decoded length exceeds `section->size - (p -
contents)` before its first output byte.
```diff
diff --git a/bfd/ihex.c b/bfd/ihex.c
@@
- BFD_ASSERT (c == ':');
+ if (c != ':')
+ goto error_return;
@@
+ if (len > section->size - (bfd_size_type) (p - contents))
+ { bfd_set_error (bfd_error_bad_value); goto error_return; }
for (i = 0; i < len; i++)
*p++ = HEX2 (buf + 2 * i);
```
The complete, apply-ready patch is included as `proposed-fix.patch`. It was
applied to a disposable checkout of the stated commit and the supplied proof of
concept was rerun without an AddressSanitizer finding.
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