CVE-2018-3870 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-2018-3871.
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Analysis
by VulDB Data Team • 03/08/2020
The vulnerability identified as CVE-2018-3870 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 that can be exploited to achieve arbitrary code execution within the targeted application environment. The vulnerability specifically manifests when the application processes specially crafted PCX image files, which are commonly used raster graphics formats that have been in use since the 1980s. The flaw exists in the image parsing logic where insufficient bounds checking occurs during the interpretation of PCX file headers and pixel data structures, allowing attackers to manipulate memory layout and potentially overwrite critical application data. This vulnerability is particularly concerning because PCX files are frequently used in graphic design workflows and can be easily embedded in various document formats, making them an attractive attack vector for social engineering campaigns. The out-of-bounds write condition creates a potential for privilege escalation or complete system compromise when successful exploitation occurs.
The technical implementation of this vulnerability stems from improper validation of PCX file structure parameters during parsing operations. When Canvas Draw attempts to interpret PCX image data, it reads header information including image dimensions, color palette data, and compression parameters without adequate verification of these values against expected ranges. The flaw occurs because the application allocates memory buffers based on potentially malicious size parameters found within the PCX file header, leading to situations where subsequent data writes exceed the allocated buffer boundaries. This type of vulnerability is classified as a CWE-787 Out-of-bounds Write according to the Common Weakness Enumeration catalog, which specifically addresses situations where programs write data past the end of allocated buffers. The attack vector requires an attacker to craft a malicious PCX file that contains malformed header values designed to trigger the buffer overflow condition, typically by specifying image dimensions that cause the application to allocate insufficient memory for the actual pixel data. The vulnerability is distinct from CVE-2018-3871, indicating that multiple memory corruption issues exist within the same application parsing functionality, suggesting a broader class of problems in the image handling codebase.
The operational impact of CVE-2018-3870 extends beyond simple application instability to potentially enable full system compromise through code execution. Successful exploitation of this vulnerability allows attackers to overwrite critical memory locations including return addresses, function pointers, or other control data structures within the application process. This memory corruption can be leveraged to redirect execution flow to attacker-controlled code, effectively enabling remote code execution within the context of the Canvas Draw application. The vulnerability is particularly dangerous in enterprise environments where graphic design applications are commonly used, as it could be exploited through email attachments, web downloads, or file sharing mechanisms. Attackers could potentially use this vulnerability to establish persistent access to systems, escalate privileges, or deploy additional malware payloads. The exploitation requires minimal user interaction beyond opening or processing the malicious PCX file, making it an attractive target for automated exploitation campaigns. Security researchers have noted that such vulnerabilities often serve as initial access points for more complex attack chains, where the initial code execution is used to establish a foothold for further reconnaissance and lateral movement within network environments.
Mitigation strategies for CVE-2018-3870 should focus on both immediate defensive measures and long-term architectural improvements to prevent similar vulnerabilities. The most effective immediate solution involves applying vendor-provided patches or updates that address the specific buffer overflow conditions in the PCX parsing code. Organizations should also implement strict file validation policies that scan and filter image files before processing them through graphic applications, particularly in environments where untrusted files may be encountered. Network-based security controls including web application firewalls and content filtering systems can help prevent malicious PCX files from reaching target systems. Additionally, the principle of least privilege should be enforced by running graphic applications with minimal required permissions, limiting the potential damage from successful exploitation attempts. From a defensive perspective, implementing memory protection mechanisms such as stack canaries, address space layout randomization, and data execution prevention can make exploitation more difficult even if the underlying vulnerability remains unpatched. The vulnerability highlights the importance of secure coding practices including bounds checking, input validation, and proper memory management, particularly when handling legacy file formats that may contain unexpected or malformed data structures. Organizations should also consider implementing automated vulnerability scanning tools that can detect similar issues in other image processing components and third-party libraries used in their graphic design workflows.