# CVE-2026-96637: Pillow: Decompression bomb check bypass in SpiderImagePlugin.seek() leads to unbounded allocation DoS


- **Severity:** High 7.1 (`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`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 21 Oct 2026
- **Updated:** 23 Oct 2026
- **Also known as:** BIT-pillow-2026-96637, DEBIAN-CVE-2026-96637, ECHO-a7ab-f10a-7131, GHSA-g842-9rc4-69pw, PYSEC-2026-4338, ROOT-APP-PYPI-CVE-2026-96637, UBUNTU-CVE-2026-96637

## What is CVE-2026-96637?

CVE-2026-96637 is a high-severity vulnerability in Python Pillow, published on 21 Oct 2026. 

### Official description

Pillow is a Python imaging library. Prior to 13.0.0, SpiderImageFile.seek() in src/PIL/SpiderImagePlugin.py reparses a later SPIDER stack frame and replaces self._size without rerunning Image._decompression_bomb_check(). A tiny file can use a safe first frame to pass Image.open() and then declare very large dimensions in a later mode F frame. Loading that frame allocates approximately four bytes per attacker-declared pixel and can consume multiple gigabytes of memory. This issue is fixed in version 13.0.0.

Weakness: CWE-409 (Improper Handling of Highly Compressed Data (Data Amplification)), CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-96637?

4 open source packages ship an affected version, including pillow. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `pillow` | Bitnami | All versions | 13.0.0 |
| `pillow` | PyPI | All versions | 13.0.0 |
| `pillow` | PyPI | All versions | 13.0.0 |
| `pillow` | PyPI | All versions | 13.0.0 |

Products: Python Pillow.

## How do I fix CVE-2026-96637?

Upgrade pillow to 13.0.0 or later.

## Is CVE-2026-96637 being exploited?

There is no known exploitation of CVE-2026-96637 in the wild and no public exploit code.

## Other vulnerabilities in Python Pillow

- [CVE-2014-3007](https://insights.sbomify.com/CVE-2014-3007/): Pillow command injection (critical 10.0)
- [CVE-2026-96639](https://insights.sbomify.com/CVE-2026-96639/): Pillow multi-frame loaders can reuse stale native image storage after mode transitions (critical 9.8)
- [CVE-2022-30595](https://insights.sbomify.com/CVE-2022-30595/): Buffer over-flow in Pillow (critical 9.8)
- [CVE-2021-25289](https://insights.sbomify.com/CVE-2021-25289/): Out of bounds write in Pillow (critical 9.8)
- [CVE-2016-4009](https://insights.sbomify.com/CVE-2016-4009/): Pillow Integer overflow in ImagingResampleHorizontal (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-96637 and fix it if it is affected.

What it is: CVE-2026-96637 is a high-severity vulnerability in Python Pillow, published on 21 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-96637 in the wild and no public exploit code.

Affected packages and fixed versions:
- pillow (Bitnami): affected all versions; fixed in 13.0.0
- pillow (PyPI): affected all versions; fixed in 13.0.0
- pillow (PyPI): affected all versions; fixed in 13.0.0
- pillow (PyPI): affected all versions; fixed in 13.0.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-96637/ (Markdown: https://insights.sbomify.com/CVE-2026-96637/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-96637
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-96637
- OSV: https://osv.dev/vulnerability/CVE-2026-96637

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-96637/
Summaries are generated and may contain mistakes; the official description above is the record.