CVE-2026-59197 Pillow: Heap out-of-bounds write in Pillow `ImageFilter.RankFilter` via integer overflow in `ImagingExpand`
An attacker can trigger a heap out-of-bounds write in Pillow's RankFilter via integer overflow, potentially leading to code execution or crashes.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59197?
CVE-2026-59197 is a high-severity memory corruption vulnerability in Python Pillow, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Pillow is a Python imaging library. Prior to 12.3.0, Pillow's public rank-filter API can trigger a native heap out-of-bounds write when given a very large odd filter size because ImageFilter.RankFilter.filter() calls image.expand(size // 2, size // 2) before rank-filter size validation and ImagingExpand() computes output dimensions with unchecked signed int arithmetic. This issue is fixed in version 12.3.0.
Which versions are affected by CVE-2026-59197?
4 open source packages ship an affected version, including pillow and Pillow. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
pillow Bitnami | All versions | 12.3.0 |
pillow PyPI | All versions | 12.3.0 |
pillow PyPI | All versions | 12.3.0 |
Pillow PyPI | All versions | 12.3.0 |
Products include Python Pillow.
How do I fix CVE-2026-59197?
Upgrade pillow to 12.3.0 or later.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-59197 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-59197 exists.
Other vulnerabilities in Python Pillow
Sources
Also known as BIT-pillow-2026-59197, CLSA-2026-1786966627, DEBIAN-CVE-2026-59197, ECHO-5231-1622-6e83, GHSA-xj96-63gp-2gmr, MINI-26cp-2wc6-rwh7 and 13 more.