CVE-2021-25291 in Pillow
Summary
by MITRE • 03/19/2021
An issue was discovered in Pillow before 8.1.1. In TiffDecode.c, there is an out-of-bounds read in TiffreadRGBATile via invalid tile boundaries.
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Analysis
by VulDB Data Team • 04/03/2021
The vulnerability identified as CVE-2021-25291 represents a critical out-of-bounds read flaw within the Pillow library version 8.1.0 and earlier, specifically affecting the TIFF image decoding functionality. This issue manifests in the TiffDecode.c source file where the TiffreadRGBATile function fails to properly validate tile boundaries during image processing operations. The vulnerability arises from insufficient input validation mechanisms that allow maliciously crafted TIFF files to trigger memory access violations when the library attempts to read data beyond allocated memory boundaries. Such flaws in image processing libraries pose significant risks as they can be exploited through various attack vectors including web applications, email systems, and file processing services that utilize Pillow for image handling.
The technical implementation of this vulnerability stems from improper boundary checking within the TIFF decoding pipeline where tile coordinates are not adequately validated before memory access operations. When processing TIFF images with malformed or specially crafted tile boundary parameters, the TiffreadRGBATile function attempts to read memory locations that fall outside the intended data structures, leading to unpredictable behavior and potential exploitation. This type of vulnerability falls under CWE-129, which specifically addresses improper validation of array indices, and represents a classic example of memory safety issues that can lead to information disclosure, denial of service, or potentially remote code execution depending on the execution environment and memory layout. The flaw is particularly concerning because it occurs during routine image processing operations, making it easily exploitable through common attack vectors.
The operational impact of CVE-2021-25291 extends beyond simple memory corruption, as it can enable attackers to perform information disclosure attacks by reading adjacent memory locations that may contain sensitive data such as cryptographic keys, user credentials, or application state information. In web environments where Pillow is used for image processing, this vulnerability can be exploited through server-side request forgery attacks, where malicious TIFF files uploaded or processed by applications can trigger the out-of-bounds read condition. The vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as attackers may leverage the memory corruption to gain additional privileges or escalate their access within compromised systems. Organizations running applications that process untrusted image files through Pillow versions prior to 8.1.1 are particularly at risk, as the flaw can be triggered through simple file uploads or web requests without requiring special privileges or complex exploitation techniques.
Mitigation strategies for CVE-2021-25291 focus primarily on upgrading to Pillow version 8.1.1 or later, which includes proper boundary validation fixes for the TIFF decoding functions. System administrators should conduct comprehensive vulnerability assessments to identify all applications and services utilizing vulnerable Pillow versions, particularly those handling user-uploaded content or processing external image files. Additional protective measures include implementing strict input validation for image files, deploying web application firewalls to filter suspicious file uploads, and establishing robust monitoring for unusual memory access patterns or application crashes that may indicate exploitation attempts. Security teams should also consider implementing sandboxing techniques for image processing operations and regularly updating all image processing libraries to ensure protection against similar vulnerabilities. The fix implemented in version 8.1.1 addresses the root cause by introducing proper validation of tile boundary parameters before memory access operations, effectively preventing the out-of-bounds read conditions that previously enabled exploitation.