CVE-2026-96641 Pillow: Reachable undefined behavior in native integer operations, potentially leading to denial of service or logic integrity compromise

What is CVE-2026-96641?

CVE-2026-96641 is a medium-severity vulnerability in Python Pillow, published on 21 Oct 2026.

Official description

Pillow is a Python imaging library. Prior to 13.0.0, PILfont text-width accumulation in src/_imaging.c checks positive glyph advances against INT_MAX but does not check negative advances against INT_MIN. Repeating a signed 16-bit advance of -32768 can therefore execute a signed C integer overflow in xsize += dx, producing a large positive width from a negative mathematical result. Applications that use getlength(), getsize(), or derived layout, quota, serialization, or allocation calculations can experience logic-integrity errors or resource consumption, while the high-level mask path commonly retains a decompression-bomb check. This issue is fixed in version 13.0.0.

Weakness: CWE-190

Which versions are affected by CVE-2026-96641?

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

Products include Python Pillow.

How do I fix CVE-2026-96641?

Upgrade pillow to 13.0.0 or later.

Is CVE-2026-96641 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-96641 exists.

Other vulnerabilities in Python Pillow

• CVE-2014-3007 Pillow command injection Critical 10.0
• CVE-2026-96639 Pillow multi-frame loaders can reuse stale native image storage after mode transitions Critical 9.8
• CVE-2022-30595 Buffer over-flow in Pillow Critical 9.8
• CVE-2021-25289 Out of bounds write in Pillow Critical 9.8
• CVE-2016-4009 Pillow Integer overflow in ImagingResampleHorizontal Critical 9.8

All Python Pillow vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BIT-pillow-2026-96641, DEBIAN-CVE-2026-96641, ECHO-c62c-e15f-df88, GHSA-4rm8-3hmm-39fg, PYSEC-2026-4340, UBUNTU-CVE-2026-96641.