The flaw is an integer overflow during buffer validation in the encode path of pillow_heif. An attacker can supply large image dimensions, causing bounds checks to be bypassed, which results in a heap out-of-bounds read. This can leak private information from process memory into encoded images or cause the process to crash, leading to information disclosure or denial of service.

Any deployment of the pillow_heif Python package before version 1.3.0 is affected. The package functions as a plugin for the Pillow image library and is commonly used in projects that process HEIF images. Versions earlier than 1.3.0 need to be patched. The pillow_heif Python package from bigcat88 is the affected component.

The CVSS base score of 5.5 yields a medium severity, and the EPSS score of less than 1 % indicates a very low probability of exploitation. The vulnerability is not present in CISA’s KEV catalog. Exploitation requires an attacker to supply a crafted HEIF image with oversized dimensions to an application that imports pillow_heif under default settings. In web services or image processing pipelines that accept external files, the attack vector is remote; local users could also trigger the flaw by processing a malicious image.