CVE-2026-59203 in Pillow
Summary
by MITRE • 07/14/2026
Pillow is a Python imaging library. From 12.0.0 through 12.2.0, Pillow's EPS parser in PIL/EpsImagePlugin.py accepts a negative byte count in the %%BeginBinary directive, allowing a crafted EPS file to cause Image.open() to seek backwards to the same directive and parse it repeatedly in an infinite loop. This issue is fixed in version 12.3.0.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 07/14/2026
The vulnerability in Pillow's EPS parser represents a classic case of input validation failure that can lead to denial of service through resource exhaustion. This flaw exists within the EpsImagePlugin.py module where the library processes Encapsulated PostScript files, which are commonly used for high-quality graphics and document exchange. The issue manifests when the parser encounters a negative byte count in the %%BeginBinary directive, a standard element used in EPS files to indicate binary data sections. This particular vulnerability allows attackers to craft malicious EPS files that can trigger an infinite loop during image parsing operations.
The technical implementation of this vulnerability stems from how Pillow handles the %%BeginBinary directive without proper validation of the byte count parameter. When a negative value is encountered, the parser's internal seek function attempts to move backwards in the file stream to reprocess the same directive repeatedly. This creates an infinite loop scenario where the application continuously parses the same section of data, consuming system resources and potentially causing the application to hang or crash. The flaw affects versions 12.0.0 through 12.2.0 of the Pillow library, making it a significant concern for applications that process user-uploaded EPS files or handle untrusted image content.
From an operational perspective, this vulnerability presents a serious denial of service risk for applications relying on Pillow for image processing. The infinite loop can cause applications to become unresponsive, consume excessive CPU resources, and potentially crash entire processes or services. This issue particularly affects web applications, document processing systems, and any software that accepts EPS files from untrusted sources without proper sanitization. The attack vector is relatively simple as it only requires crafting a malicious EPS file with a negative byte count value, making this vulnerability accessible to attackers with basic knowledge of EPS file structure.
The vulnerability aligns with CWE-129, which addresses improper validation of input ranges, and can be categorized under ATT&CK technique T1499.1 for resource exhaustion attacks. This classification reflects how the flaw enables adversaries to consume system resources through malformed input processing. The impact extends beyond simple denial of service as it can potentially be exploited in larger attack chains where resource exhaustion is used as a precursor to more sophisticated attacks. Organizations using Pillow in production environments must consider this vulnerability particularly in applications that process images from untrusted sources or implement automated image handling workflows.
Mitigation strategies include upgrading to Pillow version 12.3.0 or later, which implements proper validation of the byte count parameter in %%BeginBinary directives. Additionally, implementing input sanitization measures such as setting timeouts for image processing operations and validating file formats before parsing can provide defense-in-depth protection. Organizations should also consider employing sandboxing techniques when processing potentially malicious EPS files and implementing rate limiting for image upload operations to prevent abuse. Regular security updates and vulnerability assessments of third-party libraries form essential components of a comprehensive security posture that addresses this type of input validation flaw.