CVE-2015-1670 in Windows
Summary
by MITRE
The Windows DirectWrite library, as used in Microsoft .NET Framework 3.0 SP2, 3.5, 3.5.1, 4, 4.5, 4.5.1, and 4.5.2, allows remote attackers to obtain sensitive information from process memory via a crafted OpenType font on a web site, aka "OpenType Font Parsing Vulnerability."
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Analysis
by VulDB Data Team • 05/11/2022
The vulnerability identified as CVE-2015-1670 represents a critical information disclosure flaw within the Windows DirectWrite font rendering library that affects multiple versions of the Microsoft .NET Framework. This vulnerability specifically targets the processing of OpenType fonts within web environments, creating a pathway for remote attackers to extract sensitive data from application memory. The flaw exists in how the DirectWrite component handles malformed font files, particularly those with crafted OpenType structures that trigger unexpected memory access patterns during font parsing operations. Security researchers have classified this issue under CWE-200, which encompasses "Information Exposure Through Output Redirection" and related information leakage vulnerabilities, making it a significant concern for web applications that process untrusted font content. The vulnerability operates through the exploitation of memory corruption patterns that occur when the font parsing engine attempts to interpret malformed OpenType font data, potentially exposing sensitive information including cryptographic keys, user credentials, or application state data.
The technical mechanism behind CVE-2015-1670 involves the manipulation of OpenType font files that contain specially crafted structures designed to trigger memory access violations within the DirectWrite library. When a web application processes such malicious fonts, the font parsing code executes with insufficient input validation, allowing attackers to cause the system to inadvertently reveal memory contents through side-channel information leakage. The vulnerability specifically affects the handling of font tables and metadata within the OpenType format, where malformed entries can cause the parsing engine to access memory locations beyond the intended font data boundaries. This memory access pattern can result in the exposure of sensitive information stored in adjacent memory regions, including stack contents, heap data, or other process memory segments. The attack vector requires only that a victim visits a malicious website containing the crafted font file, making it particularly dangerous for web applications and content management systems that allow user-uploaded font resources. According to ATT&CK framework category T1059, this vulnerability represents a technique for executing malicious code through application-specific input processing, while also aligning with T1552 for data manipulation and information gathering through memory access techniques.
The operational impact of CVE-2015-1670 extends beyond simple information disclosure, as the exposed memory contents could contain highly sensitive data that could be leveraged for further attacks within the compromised system. Attackers could potentially extract cryptographic keys used for SSL/TLS encryption, application credentials, session tokens, or other confidential information that would otherwise remain protected. The vulnerability affects a broad range of Microsoft products including .NET Framework versions 3.0 SP2 through 4.5.2, making it particularly widespread across enterprise environments that utilize legacy or extended support frameworks. Organizations running web applications that process user-generated content, including those with rich text editors or font customization features, face elevated risk from this vulnerability. The attack requires no special privileges or user interaction beyond visiting the malicious website, making it particularly effective for large-scale information gathering campaigns. Additionally, the vulnerability's exploitation can be automated through web-based attack frameworks, allowing threat actors to systematically harvest sensitive information from multiple targets. This makes CVE-2015-1670 particularly dangerous in environments where web applications process untrusted font content or where users can upload font files for use in web applications. The vulnerability's persistence across multiple .NET Framework versions indicates a fundamental flaw in the font parsing implementation that required comprehensive patching across the entire affected product line. Organizations implementing security controls should consider network segmentation, web application firewalls, and input validation measures to mitigate the risk of exploitation, while also ensuring that all affected systems receive appropriate security updates to address the underlying memory access vulnerability in the DirectWrite library implementation.