CVE-2018-3871 in Canvas Draw
Summary
by MITRE
An exploitable out-of-bounds write exists in the PCX parsing functionality of Canvas Draw version 4.0.0. A specially crafted PCX image processed via the application can lead to an out-of-bounds write, overwriting arbitrary data. An attacker can deliver a PCX image to trigger this vulnerability and gain code execution. A different vulnerability than CVE-2018-3870.
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Analysis
by VulDB Data Team • 04/18/2023
The vulnerability identified as CVE-2018-3871 represents a critical out-of-bounds write flaw within the PCX image parsing component of Canvas Draw version 4.0.0. This issue falls under the category of memory corruption vulnerabilities and specifically manifests as a buffer overflow condition that occurs during the processing of specially crafted PCX image files. The flaw stems from inadequate input validation and boundary checking mechanisms within the application's image parsing engine, which fails to properly validate the dimensions and data structure of incoming PCX files before attempting to parse and render them. The vulnerability is classified as an out-of-bounds write according to CWE-787, which describes a condition where a program writes data past the end or before the beginning of the buffer, and it represents a direct threat to the application's memory integrity and overall system security.
The technical exploitation of this vulnerability occurs when Canvas Draw processes a maliciously constructed PCX image file that contains malformed data structures or incorrect dimension specifications. During the parsing operation, the application's PCX handler fails to properly validate buffer boundaries, allowing an attacker to craft a PCX file that causes the parser to write data beyond the allocated memory space intended for the image data. This out-of-bounds write can overwrite adjacent memory locations, potentially corrupting critical program data, function pointers, or return addresses, which provides an attacker with the opportunity to manipulate program execution flow. The vulnerability is particularly dangerous because it allows for arbitrary code execution, as the overwritten memory locations can be strategically positioned to redirect program control flow or overwrite executable code segments.
The operational impact of CVE-2018-3871 extends beyond simple data corruption, presenting a severe threat to system integrity and user security. An attacker who successfully exploits this vulnerability can gain complete control over the affected system, potentially executing malicious code with the privileges of the Canvas Draw application user. The vulnerability's exploitation requires only the delivery of a specially crafted PCX image file, making it particularly dangerous in environments where users might encounter such files through email attachments, web downloads, or file sharing mechanisms. This vulnerability aligns with ATT&CK technique T1203, which describes the use of malicious files to gain execution privileges, and represents a classic example of a file format parsing vulnerability that can be leveraged for privilege escalation and persistent access to target systems.
Mitigation strategies for CVE-2018-3871 should focus on both immediate defensive measures and long-term architectural improvements. Users should immediately update to the latest version of Canvas Draw that contains patches addressing this vulnerability, as the vendor would have implemented proper input validation and boundary checking mechanisms to prevent the out-of-bounds write condition. Organizations should implement file type filtering and validation measures at network perimeters to prevent the delivery of potentially malicious PCX files to end users. Additionally, application sandboxing and memory protection mechanisms such as address space layout randomization and data execution prevention should be enabled to limit the impact of successful exploitation attempts. The vulnerability demonstrates the importance of following secure coding practices and adheres to CWE principles that emphasize proper input validation, buffer size checking, and memory management to prevent similar issues in image processing and file format handling components.