CVE-2018-7639 in CImg
Summary
by MITRE
An issue was discovered in CImg v.220. A heap-based buffer over-read in load_bmp in CImg.h occurs when loading a crafted bmp image, a different vulnerability than CVE-2018-7588. This is in a "16 bits colors" case, aka case 16.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2018-7639 represents a critical heap-based buffer over-read flaw within the CImg library version 220, specifically manifesting during the processing of maliciously crafted bitmap image files. This vulnerability resides in the load_bmp function within the CImg.h header file and is particularly triggered when handling bitmap images with 16-bit color depth configuration. The flaw demonstrates characteristics consistent with CWE-125, which describes out-of-bounds read conditions that occur when a program reads data beyond the boundaries of a buffer, potentially exposing sensitive memory contents or enabling arbitrary code execution. The vulnerability operates under the broader category of memory safety issues that have historically been exploited in image processing libraries due to insufficient input validation and boundary checking mechanisms.
The technical implementation of this vulnerability stems from inadequate validation of bitmap file headers and color depth specifications during the image loading process. When the load_bmp function encounters a crafted bmp file with 16-bit color configuration, the library fails to properly validate the expected buffer sizes and memory allocations required for processing the image data. This insufficient boundary checking allows an attacker to construct a malicious bitmap file that causes the application to read beyond allocated memory boundaries, potentially accessing adjacent memory regions containing sensitive data or system information. The vulnerability specifically affects the 16-bit color case, indicating that the flaw is not present in all bitmap color depth configurations, but rather in the particular handling logic for 16-bit color formats. This targeted nature suggests that the error occurs during the specific data parsing routine responsible for 16-bit color palette interpretation and memory allocation.
The operational impact of CVE-2018-7639 extends beyond simple data corruption, as it can potentially enable remote code execution or information disclosure when applications utilizing the vulnerable CImg library process untrusted bitmap files. Attackers can exploit this vulnerability by crafting malicious bitmap images that, when loaded by vulnerable applications, trigger the buffer over-read condition. This vulnerability is particularly dangerous in environments where applications automatically process user-uploaded images or where bitmap files are fetched from untrusted sources without proper sanitization. The implications align with ATT&CK technique T1203, which covers legitimate programs that are used to execute malicious code, as the vulnerability allows attackers to leverage the legitimate image processing functionality to achieve unauthorized access. The vulnerability can be exploited in web applications, desktop software, and any system that relies on CImg for bitmap image processing, making it a significant concern for software vendors and system administrators.
Mitigation strategies for CVE-2018-7639 should prioritize immediate patching of affected CImg library versions to address the buffer over-read condition. Organizations should implement comprehensive input validation measures that include strict header checking and color depth verification before image processing operations. The recommended approach involves upgrading to patched versions of the CImg library where the boundary checking has been enhanced to prevent buffer over-reads during 16-bit color bitmap processing. Additionally, application developers should implement defensive programming practices such as bounds checking, memory allocation validation, and proper error handling when processing external image files. Security measures should include sandboxing image processing operations, implementing strict file format validation, and monitoring for unusual memory access patterns that could indicate exploitation attempts. The vulnerability highlights the importance of thorough input validation in multimedia processing libraries and underscores the need for regular security assessments of third-party components used in application development. Organizations should also consider implementing network-level controls to prevent the delivery of potentially malicious image files to systems that utilize vulnerable CImg implementations.