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Response snapshot Oct 26, 2026, 22:02 UTC

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VulnerabilityCVE-2026-96636

Pillow: Decompression-bomb protection bypass via multi-frame seek() in MPO and DCX (MpoImageFile.seek / DcxImageFile.seek)

Same class as the recently assigned CVE-2026-55379 (BdfFontFile), CVE-2026-55380 (GdImageFile) and CVE-2026-40192 (FITS GZIP). - **`PIL/MpoImagePlugin.py`, `MpoImageFile.seek()`**: calls `JpegImagePlugin.JpegImageFile._open(self)` (which sets `self.

Published Updated

At a glance

Exploited
Not known
Severity
6.5 Medium (CVSS 3.1)
Chance of exploitation
0.4% in the next 30 days
Sources
1 source

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-p8hx-v2p6-rp84 (opens a new tab)

What happened

### 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:

Continue reading

- **`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`:

```python 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:

```python # 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 — end of DcxImageFile.seek() PcxImageFile._open(self) Image._decompression_bomb_check(self.size) # add ```

Affected package ranges reported by GitHub: Pillow: < 13.0.0

Scores and how they were measured

CVSS base severity

6.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H

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 28.4%

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-p8hx-v2p6-rp84 (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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, 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-p8hx-v2p6-rp84, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  12. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-96636, 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 22). Pillow: Decompression-bomb protection bypass via multi-frame seek() in MPO and DCX (MpoImageFile.seek / DcxImageFile.seek) (CVE-2026-96636). https://kevwire.com/record/CVE-2026-96636

MLA

"Pillow: Decompression-bomb protection bypass via multi-frame seek() in MPO and DCX (MpoImageFile.seek / DcxImageFile.seek) (CVE-2026-96636)." KEVWire, 22 Oct. 2026, kevwire.com/record/CVE-2026-96636.

Chicago

KEVWire. "Pillow: Decompression-bomb protection bypass via multi-frame seek() in MPO and DCX (MpoImageFile.seek / DcxImageFile.seek) (CVE-2026-96636)." Last modified October 22, 2026. https://kevwire.com/record/CVE-2026-96636.

Evidence summary (plain text)

Pillow: Decompression-bomb protection bypass via multi-frame seek() in MPO and DCX (MpoImageFile.seek / DcxImageFile.seek) (Oct 22, 2026).
Same class as the recently assigned CVE-2026-55379 (BdfFontFile), CVE-2026-55380 (GdImageFile) and CVE-2026-40192 (FITS GZIP).

- **`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.
CVSS 6.5 (version 3.1; evidence as of Oct 22, 2026; https://github.com/advisories/GHSA-p8hx-v2p6-rp84).
EPSS 0.4% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-96636&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-p8hx-v2p6-rp84: https://github.com/advisories/GHSA-p8hx-v2p6-rp84
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
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-96636&date=2026-10-26
Record ID: CVE-2026-96636.
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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