CVE-2015-4696 in libwmf
Summary
by MITRE
Use-after-free vulnerability in libwmf 0.2.8.4 allows remote attackers to cause a denial of service (crash) via a crafted WMF file to the (1) wmf2gd or (2) wmf2eps command.
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Analysis
by VulDB Data Team • 05/22/2022
The CVE-2015-4696 vulnerability represents a critical use-after-free flaw in the libwmf library version 0.2.8.4 which serves as a core component for handling Windows Metafile format graphics files. This vulnerability exists within the command-line utilities wmf2gd and wmf2eps that are designed to convert WMF files into different graphic formats. The flaw stems from improper memory management during the processing of malformed WMF files, creating conditions where freed memory regions are accessed after being deallocated. Such vulnerabilities fall under the CWE-416 category of Use After Free, which is classified as a serious memory corruption issue that can lead to arbitrary code execution or system instability.
The technical exploitation of this vulnerability occurs when remote attackers craft specially malformed WMF files that trigger memory deallocation followed by subsequent access attempts within the libwmf processing pipeline. When the wmf2gd or wmf2eps utilities encounter these crafted files, they fail to properly validate the input structure, leading to the allocation and immediate deallocation of memory blocks that are later referenced. This creates a classic use-after-free scenario where the application attempts to access memory that has already been freed, causing segmentation faults and application crashes. The vulnerability specifically affects the memory management functions within the library's parsing routines, particularly those handling complex WMF graphic elements and their associated data structures.
From an operational impact perspective, this vulnerability creates significant denial of service risks for systems that process WMF files through the affected command-line utilities. Organizations relying on these tools for document conversion, graphic processing, or automated workflow systems face potential service interruptions when malicious WMF files are introduced into their processing pipelines. The remote nature of the attack means that adversaries can trigger the vulnerability without requiring local access, making it particularly dangerous for web applications, email systems, or any service that accepts WMF file uploads. The vulnerability can be exploited across multiple platforms where libwmf is installed, potentially affecting servers, workstations, and embedded systems that utilize these conversion utilities.
Security mitigations for CVE-2015-4696 should focus on immediate patching of the libwmf library to version 0.2.8.5 or later, which contains the necessary memory management fixes. System administrators should implement input validation measures that sanitize WMF file inputs before processing, including signature verification and structural integrity checks. Network-level protections such as content filtering and sandboxing mechanisms should be deployed to prevent malicious WMF files from reaching vulnerable systems. Additionally, organizations should consider disabling or removing the affected wmf2gd and wmf2eps utilities from production environments until proper patches are applied. The ATT&CK framework categorizes this vulnerability under T1203 - Exploitation for Client Execution and T1059 - Command and Scripting Interpreter, highlighting the potential for escalation through compromised systems. Organizations should also monitor for indicators of compromise related to WMF file processing and implement comprehensive logging to detect exploitation attempts. The vulnerability demonstrates the importance of proper memory management in open source libraries and the need for regular security assessments of third-party components used in critical infrastructure.