CVE-2018-12932 in Wine
Summary
by MITRE
PlayEnhMetaFileRecord in enhmetafile.c in Wine 3.7 allows attackers to cause a denial of service (heap-based buffer overflow) or possibly have unspecified other impact by triggering a large pAlphaBlend->cbBitsSrc value.
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Analysis
by VulDB Data Team • 03/29/2023
The vulnerability identified as CVE-2018-12932 resides within the Wine compatibility layer implementation, specifically in the PlayEnhMetaFileRecord function located in the enhmetafile.c source file. This flaw affects Wine version 3.7 and represents a critical heap-based buffer overflow condition that can be exploited through manipulation of the pAlphaBlend->cbBitsSrc parameter. The vulnerability manifests when the system processes enhanced metafile records, which are used to store graphical operations in Windows-compatible applications running under Wine. This particular implementation flaw demonstrates a classic buffer overflow vulnerability where insufficient bounds checking occurs during processing of graphical data structures.
The technical execution of this vulnerability occurs when an attacker crafts a specially formatted enhanced metafile that contains an excessively large value for the cbBitsSrc field within the pAlphaBlend structure. This parameter typically represents the size of source bitmap data in bytes, but when manipulated to exceed expected boundaries, it causes the heap allocation to overflow. The flaw operates at the intersection of Windows graphics API compatibility and memory management within the Wine environment, creating a scenario where legitimate graphical operations can be transformed into memory corruption events. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, though the heap-based nature of the actual exploitation makes it more complex to analyze. This type of vulnerability falls within the ATT&CK framework under T1059.007 for Windows Subsystem and T1203 for Exploitation for Client Execution, as it represents a client-side exploitation vector through graphical rendering.
The operational impact of CVE-2018-12932 extends beyond simple denial of service conditions, as the heap corruption can potentially lead to arbitrary code execution or system instability. When the buffer overflow occurs, it can corrupt adjacent heap memory, leading to unpredictable behavior including application crashes, data corruption, or in more severe cases, privilege escalation opportunities. The vulnerability affects any application that relies on Wine's enhanced metafile processing capabilities, which includes a broad range of Windows software that utilizes graphical operations. Attackers can leverage this vulnerability by delivering malicious enhanced metafiles through various attack vectors including email attachments, web downloads, or compromised software installations. The heap-based nature of the overflow makes detection more challenging as it may not immediately cause system crashes, allowing for more subtle exploitation techniques that could persist longer within target environments.
Mitigation strategies for this vulnerability require immediate patching of Wine installations to versions that address the buffer overflow in the PlayEnhMetaFileRecord function. System administrators should ensure all Wine components are updated to versions that include proper bounds checking for the cbBitsSrc parameter. Additional protective measures include implementing strict file validation for enhanced metafile processing, monitoring for unusual memory allocation patterns, and employing sandboxing techniques to limit the impact of potential exploitation. Network security controls should be configured to filter or scan for potentially malicious enhanced metafile content, particularly in environments where users may encounter untrusted graphical content. The vulnerability highlights the importance of proper input validation in compatibility layers and demonstrates how seemingly benign graphical operations can become attack vectors when insufficient boundary checks are implemented. Organizations should also consider implementing automated patch management systems to ensure timely updates to Wine components and maintain protection against similar vulnerabilities in the broader compatibility layer ecosystem.