CVE-2026-59197

A flaw was found in Pillow prior to 12.3.0. The public RankFilter API can trigger a native heap out-of-bounds write when given a very large odd filter size. ImageFilter.RankFilter.filter() calls image.expand(size // 2, size // 2) before rank-filter size validation, and ImagingExpand() computes output dimensions with unchecked signed integer arithmetic. This can lead to denial of service and limited integrity impact via heap corruption.

Pillow's RankFilter API is vulnerable to a native heap out-of-bounds write when a caller supplies a very large odd filter size. Expansion runs before size validation and ImagingExpand uses unchecked signed integer arithmetic for output dimensions. A remote attacker who can drive RankFilter with attacker-controlled sizes may crash the process or corrupt heap memory. Fixed in Pillow 12.3.0.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.