CVE-2026-96636

Summary

Pillow's decompression-bomb protection (Image._decompression_bomb_check, gated by Image.MAX_IMAGE_PIXELS) is enforced only on the first frame, inside Image.open(). For multi-frame formats, seek() re-parses the target frame's header and resets self._size. GifImagePlugin and TiffImagePlugin re-run the bomb check on seek(), but MpoImageFile.seek() and DcxImageFile.seek() do not. A crafted MPO or DCX whose first frame is tiny (passing the check) but whose later frame declares enormous dimensions therefore bypasses the protection: loading that frame decodes an over-limit image and commits large amounts of memory — a denial of service (memory exhaustion / OOM).

Same class as the recently assigned CVE-2026-55379 (BdfFontFile), CVE-2026-55380 (GdImageFile) and CVE-2026-40192 (FITS GZIP).

Details

Image.open() → _open_core() runs _decompression_bomb_check(im.size) once, on the frame present at open time. Both vulnerable seek() methods re-parse a new frame and set a new self._size without re-checking:

• PIL/MpoImagePlugin.py, MpoImageFile.seek(): calls JpegImagePlugin.JpegImageFile._open(self) (which sets self._size from the frame's JPEG SOF) and rebuilds self.tile, with no Image._decompression_bomb_check(self.size).
• PIL/DcxImagePlugin.py, DcxImageFile.seek(): calls PcxImageFile._open(self) (which sets self._size from the page's PCX header), with no check.

Confirmed present in 12.3.0 (latest release) and on main (13.0.0.dev0). Compare GifImagePlugin._seek and TiffImagePlugin, which call _decompression_bomb_check correctly on seek.

PoC

Self-contained; the victim uses default MAX_IMAGE_PIXELS:

import io
from PIL import Image

# attacker builds the file (guard disabled only to CREATE the oversized frame)
Image.MAX_IMAGE_PIXELS = None
small = Image.new("RGB", (8, 8))
big   = Image.new("RGB", (14000, 14000), (120, 60, 30))   # 196,000,000 px > error threshold
buf = io.BytesIO()
small.save(buf, format="MPO", save_all=True, append_images=[big])
data = buf.getvalue()                                      # ~3 MB
Image.MAX_IMAGE_PIXELS = int(1024 * 1024 * 1024 // 4 // 3) # restore default

# victim (default limits)
im = Image.open(io.BytesIO(data))   # frame 0 (8x8) passes the bomb check
im.seek(1)                          # frame 1 (14000x14000) -> NOT re-checked  <-- bug
im.load()                           # decodes the over-limit image, commits memory
print("loaded over-limit frame:", im.size)

Measured on Pillow 12.3.0 (default limit 89,478,485 px; error threshold 178,956,970 px):

| Vector | File size | Frame 1 | Peak RSS | |---|---|---|---| | MPO (JPEG) | ~3.0 MB | 14000×14000 (196 Mpx) | ~763 MB | | DCX (PCX) | ~6.2 MB | 14000×14000 (196 Mpx) | ~200 MB | | Control: same image standalone | — | 196 Mpx | DecompressionBombError (correctly blocked) |

The DCX vector (0x3ADE68B1 magic + offset directory + two PCX pages) behaves identically via DcxImageFile.seek(). Scaling frame 1 toward JPEG's ~65500×65500 maximum drives multi-GB commitments from a small file, reliably OOM-killing the process.

Impact

Denial of service (memory exhaustion / OOM) — CWE-400 / CWE-1284, a bypass of Pillow's documented decompression-bomb mitigation. seek() + load() is the normal way to iterate frames (e.g. PIL.ImageSequence.Iterator, thumbnailers, converters, 3D-photo handlers). Because MPO is auto-detected from a JPEG carrying MPF metadata, a file served with a .jpg extension can be opened as MPO, so any application that iterates frames of untrusted images is exposed.

Suggested fix

Re-run the check after seek() re-parses a frame, mirroring GIF/TIFF:

# PIL/MpoImagePlugin.py — end of MpoImageFile.seek()
self.tile = [ImageFile._Tile("jpeg", (0, 0) + self.size, self.offset, self.tile[0][-1])]
Image._decompression_bomb_check(self.size)   # add
self.__frame = frame

# PIL/DcxImagePlugin.py…

Pillow is a Python imaging library. Prior to 13.0.0, MpoImageFile.seek() and DcxImageFile.seek() reparse later MPO or DCX frames and replace self._size without rerunning Image._decompression_bomb_check(). A crafted multi-frame image can use a tiny first frame to pass Image.open() and then declare an over-limit later frame. Normal frame iteration through seek(), load(), or ImageSequence.Iterator can decode that frame and commit hundreds of megabytes or more, causing memory-exhaustion denial of service. This issue is fixed in version 13.0.0.

Pillow is a Python imaging library. Prior to 13.0.0, MpoImageFile.seek() and DcxImageFile.seek() reparse later MPO or DCX frames and replace self._size without rerunning Image._decompression_bomb_check(). A crafted multi-frame image can use a tiny first frame to pass Image.open() and then declare an over-limit later frame. Normal frame iteration through seek(), load(), or ImageSequence.Iterator can decode that frame and commit hundreds of megabytes or more, causing memory-exhaustion denial of service. This issue is fixed in version 13.0.0.

Pillow is a Python imaging library. Prior to 13.0.0, MpoImageFile.seek() and DcxImageFile.seek() reparse later MPO or DCX frames and replace self._size without rerunning Image._decompression_bomb_check(). A crafted multi-frame image can use a tiny first frame to pass Image.open() and then declare an over-limit later frame. Normal frame iteration through seek(), load(), or ImageSequence.Iterator can decode that frame and commit hundreds of megabytes or more, causing memory-exhaustion denial of service. This issue is fixed in version 13.0.0.

TuxCare rebuilt pillow to address 3 CVEs. Fixed in 11.3.0.post12+tuxcare.

TuxCare rebuilt pillow to address 9 CVEs. Fixed in 11.2.1.post13+tuxcare.

TuxCare rebuilt pillow to address 8 CVEs. Fixed in 10.4.0.post15+tuxcare.

TuxCare rebuilt pillow to address 7 CVEs. Fixed in 9.5.0.post13+tuxcare.

These are all security issues fixed in the python313-Pillow-13.0.0-2.1 package on the GA media of openSUSE Tumbleweed.

This update for python-Pillow fixes the following issues:

• CVE-2026-96636: decompression-bomb protection bypass via multi-frame seek() in MPO and DCX (bsc#1286802).
• CVE-2026-96637: decompression bomb check bypass in SpiderImagePlugin.seek() leads to unbounded allocation DoS (bsc#1286801).
• CVE-2026-96640: PDF append accepts malformed shared page-tree DAG, which can cause resource exhaustion (bsc#1286798).
• CVE-2026-96641: reachable undefined behavior in native integer operations can lead to denial of service or logic integrity compromise (bsc#1286797).
• CVE-2026-96642: TarIO negative size field causes infinite CPU-spin loop (bsc#1286796).
• CVE-2026-112390: Denial of Service via infinite loop during crafted MIC image parsing (bsc#1286256).
• CVE-2026-112391: Denial of Service via unbounded recursion in PDF parser (bsc#1286273).
• CVE-2026-112392: Denial of Service via zero-size images in rank filters (bsc#1286287).
• CVE-2026-112393: heap buffer overflow and stale-heap disclosure in _tiffWriteProc when saving compressed TIFF data (bsc#1286325).
• CVE-2026-112394: P;2L and P;4L decoders may read 1 to 3 bytes past the passed buffer size (bsc#1286311).
• CVE-2026-112397: out-of-bounds access in _imagingmorph on a zero-width image (bsc#1286314).
• CVE-2026-112398: heap buffer overflow in FPX JPEG decoding can lead to code execution (bsc#1286406).
• CVE-2026-112399: Denial of service via crafted APNG image (bsc#1286368).
• CVE-2026-112400: Denial of Service via memory exhaustion from crafted GIF image (bsc#1286370).
• CVE-2026-112401: Denial of Service via crafted GIF comments (bsc#1286372).
• CVE-2026-112402: Denial of service via double free during image transformation (bsc#1286381).
• CVE-2026-112403: heap buffer overflow in ImagingJpegDecode allows for code execution (bsc#1286405).
• CVE-2026-112405: NULL pointer dereference in Image.merge via an unvalidated band 0 (bsc#1286404).
• CVE-2026-112406: infinite loop in PdfParser.rewrite_pages on page tree Parent cycle (bsc#1286403).
• CVE-2026-112891: quadratic GIF comment copying during save (bsc#1286402).
• CVE-2026-112892: MSP RLE decoder expands a tiny file into unbounded memory (bsc#1286401).
• CVE-2026-112894: Denial of Service via crafted multi-frame image conversion (bsc#1286408).
• CVE-2026-112895: Denial of service via crafted PDF during append operations (bsc#1286411).
• CVE-2026-112896: TIFF encoder ColorMap plane-size mismatch causes a heap out-of-bounds read (bsc#1286400).
• CVE-2026-112897: TiffDecode returns uninitialized memory as pixels for short JPEG strips (bsc#1286398).
• CVE-2026-112899: EPS load(scale) lets Ghostscript render past the decompression bomb limit (bsc#1286489).
• CVE-2026-112900: argument Injection in Ghostscript call can lead to remote code execution (bsc#1286397).
• CVE-2026-112901: ReDoS in XbmImagePlugin can be triggered by 512-byte file (bsc#1286396).
• CVE-2026-112902: memory disclosure and segfault in libtiff encoder via crafted TIFF tags (bsc#1286804).