CVE-2018-7637 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 colors" case, aka case 4.
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Analysis
by VulDB Data Team • 02/16/2023
The vulnerability identified as CVE-2018-7637 represents a critical heap-based buffer over-read flaw within the CImg library version 220. This issue specifically manifests during the processing of bitmap image files through the load_bmp function in the CImg.h header file. The vulnerability is particularly concerning as it enables remote code execution or system compromise when an application utilizing CImg processes maliciously crafted bitmap images. The flaw exists in what is termed the "16 colors" case, designated as case 4 within the library's implementation, making it a targeted attack vector for adversaries seeking to exploit image processing applications. The vulnerability demonstrates the inherent risks associated with image parsing libraries that fail to properly validate input data structures, particularly when dealing with legacy bitmap formats that have specific color depth requirements.
Technical exploitation of this vulnerability occurs when the load_bmp function attempts to parse a specially crafted bmp file that contains 16 colors, triggering an improper memory access pattern that reads beyond allocated buffer boundaries. The heap-based nature of the over-read indicates that the vulnerability operates within dynamically allocated memory regions, potentially allowing attackers to access sensitive data or manipulate memory layout. This type of flaw falls under the Common Weakness Enumeration category CWE-125, which describes "Out-of-bounds Read" conditions where programs access memory beyond the intended bounds. The specific implementation issue arises from inadequate bounds checking during the parsing of the bitmap file header and color table entries, particularly when processing 16-color bitmap images where the expected memory layout differs from standard color depths. The vulnerability demonstrates how seemingly benign image processing operations can become attack vectors when proper input validation and memory management controls are absent.
The operational impact of CVE-2018-7637 extends across numerous applications that utilize the CImg library for image processing tasks, including but not limited to graphic design software, image viewers, document management systems, and web applications that handle user-uploaded images. Attackers can leverage this vulnerability by crafting malicious bitmap files that, when processed by vulnerable applications, trigger the buffer over-read condition. This can lead to arbitrary code execution, denial of service conditions, or information disclosure depending on the specific implementation and system configuration. The vulnerability is particularly dangerous in web environments where users can upload images, as it allows for server-side exploitation without requiring user interaction beyond the image upload process. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter and T1203 for exploitation for privilege escalation, as successful exploitation can provide attackers with persistent access to systems through compromised image processing pipelines.
Mitigation strategies for CVE-2018-7637 require immediate action from system administrators and developers utilizing the affected CImg library version. The most effective solution involves upgrading to a patched version of the CImg library where the buffer over-read condition has been addressed through proper bounds checking and input validation mechanisms. Organizations should conduct comprehensive vulnerability assessments to identify all applications and systems that rely on the vulnerable library version, particularly those handling user-uploaded content or processing external image files. Additional defensive measures include implementing strict input validation for image files, employing sandboxing techniques for image processing operations, and deploying network-based intrusion detection systems to monitor for exploitation attempts. The vulnerability highlights the importance of maintaining up-to-date third-party libraries and implementing robust security testing procedures that include fuzzing and memory safety analysis to prevent similar issues in other image processing components. Regular security audits and dependency monitoring should be implemented to ensure early detection of similar vulnerabilities in other open source libraries used throughout the organization's software ecosystem.