CVE-2026-25990 is an out-of-bounds write vulnerability classified under CWE-787 found in the python-pillow Pillow library, specifically triggered when loading specially crafted PSD (Photoshop Document) image files. This vulnerability affects Pillow versions starting from 10.3.0 up to but excluding 12.1.1, with the issue resolved in version 12.1.1. The out-of-bounds write occurs due to improper bounds checking during the parsing of PSD image data, allowing an attacker to overwrite adjacent memory regions. This can lead to arbitrary code execution, memory corruption, or application crashes. The vulnerability is remotely exploitable without requiring any privileges or user interaction, as it can be triggered simply by processing a malicious PSD file. Pillow is a widely used Python imaging library leveraged in numerous applications for image manipulation, web services, and automated processing pipelines, making this vulnerability impactful across many sectors. The CVSS 4.0 score of 8.9 reflects the high potential for confidentiality, integrity, and availability impacts. Although no exploits have been reported in the wild yet, the ease of exploitation and the critical nature of the vulnerability necessitate urgent attention. The vulnerability does not require authentication, increasing the attack surface, especially for exposed services that accept image uploads or process images from untrusted sources.

For European organizations, the impact of CVE-2026-25990 can be significant. Organizations that utilize Pillow for image processing in web applications, content management systems, or automated workflows risk remote code execution or denial of service attacks if they process untrusted PSD files. This could lead to data breaches, service outages, or compromise of internal systems. Industries such as media, publishing, e-commerce, and software development are particularly at risk due to their reliance on image handling. Additionally, critical infrastructure or government services using Python-based image processing tools could face operational disruptions or targeted attacks. The vulnerability’s ability to be exploited without authentication or user interaction broadens the threat landscape, potentially allowing attackers to compromise systems simply by submitting malicious images. This elevates the risk for cloud service providers and SaaS platforms operating in Europe that offer image upload features. The potential for arbitrary code execution also raises concerns about lateral movement within networks and persistent footholds for attackers.

European organizations should immediately upgrade all instances of the Pillow library to version 12.1.1 or later, where the vulnerability is patched. Beyond patching, organizations should implement strict validation and sanitization of all uploaded or processed image files, especially PSD files, to detect and block malformed or suspicious content. Employing runtime memory protection mechanisms such as Address Space Layout Randomization (ASLR), Data Execution Prevention (DEP), and control flow integrity can help mitigate exploitation attempts. Network-level controls should restrict access to image processing services to trusted users or systems where feasible. Security teams should monitor logs for unusual crashes or memory errors related to image processing components. Incorporating fuzz testing and static analysis in the development lifecycle can help identify similar vulnerabilities proactively. Finally, organizations should educate developers and system administrators about the risks of processing untrusted image data and enforce secure coding practices around third-party libraries.