CVE-2021-25290 in Pillow
Summary
by MITRE • 03/19/2021
An issue was discovered in Pillow before 8.1.1. In TiffDecode.c, there is a negative-offset memcpy with an invalid size.
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Analysis
by VulDB Data Team • 03/31/2026
The vulnerability identified as CVE-2021-25290 represents a critical memory safety issue within the Pillow library version 8.1.0 and earlier, specifically affecting the TIFF image decoding functionality. This flaw exists in the TiffDecode.c source file where a negative-offset memcpy operation is performed with an invalid size parameter, creating a potential avenue for memory corruption and arbitrary code execution. The vulnerability arises from insufficient input validation during TIFF image processing, particularly when handling malformed or specially crafted image files that contain malicious offset values.
This memory corruption vulnerability falls under the category of buffer over-read and memory corruption issues, which are commonly classified as CWE-121 and CWE-125 in the Common Weakness Enumeration catalog. The technical flaw manifests when the TIFF decoder attempts to process image data with negative offset values that result in invalid memory access patterns during the memcpy operation. The negative offset causes the memory copying function to reference memory locations outside the intended buffer boundaries, potentially leading to information disclosure, application crashes, or more severe exploitation outcomes. The invalid size parameter compounds the issue by creating unpredictable memory access patterns that bypass normal safety checks.
The operational impact of this vulnerability extends beyond simple application instability, as it can be exploited by attackers who craft malicious TIFF files designed to trigger the specific memory corruption scenario. When an application using Pillow processes such malformed images, the vulnerability can lead to denial of service conditions or potentially enable remote code execution depending on the execution environment and memory layout. The attack surface is particularly broad given that TIFF format is widely supported across various applications, making this vulnerability relevant to web applications, image processing systems, and content management platforms that utilize Pillow for image handling. This vulnerability aligns with ATT&CK technique T1203 by enabling process injection and memory corruption attacks that can be leveraged for privilege escalation or system compromise.
Mitigation strategies for CVE-2021-25290 primarily focus on immediate patching of the Pillow library to version 8.1.1 or later, which includes proper bounds checking and validation of offset parameters during TIFF decoding operations. Organizations should implement comprehensive input validation for all image processing workflows, particularly when handling untrusted user uploads or third-party image content. Additional protective measures include deploying sandboxed image processing environments, implementing strict file format validation, and utilizing memory safety features such as address space layout randomization and stack canaries. System administrators should also consider implementing network-based intrusion detection systems to monitor for potential exploitation attempts involving malformed image files, while application developers should ensure proper error handling and resource cleanup mechanisms are in place to prevent exploitation of memory corruption vulnerabilities.