An out‑of‑bounds write occurs when Pillow processes specially crafted PSD files in versions between 10.3.0 and prior to 12.1.1. The flaw arises from improper bounds checking of the image data buffer, allowing a malicious PSD to overwrite memory beyond the intended allocation. This can result in arbitrary code execution, privilege escalation, or application crash, as defined by CWE‑787. The CVSS base score of 8.6 signals critical severity.

Products affected are those that include Pillow under the python‑pillow:Pillow designation. Vulnerable releases span Pillow 10.3.0 through 12.1.0, inclusive. The vulnerability is fixed in Pillow 12.1.1 and any later versions. Systems that run Python applications that import Pillow for image handling—particularly those that render or process PSD files—are at risk.

Risk assessment places the weakness at high severity; however, the EPSS score of less than 1 % suggests a low likelihood of exploitation at present, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. The attack vector is likely remote or local, depending on whether the affected application accepts user‑supplied PSD images. An adversary could supply a malicious PSD file to a vulnerable service or library, triggering the buffer overflow and potentially executing arbitrary code or causing denial of service.