CVE-2015-2435 in Windows
Summary
by MITRE
Microsoft Windows Vista SP2, Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT Gold and 8.1, Windows 10, Office 2007 SP3 and 2010 SP2, Live Meeting 2007 Console, Lync 2010, Lync 2010 Attendee, Lync 2013 SP1, Lync Basic 2013 SP1, and Silverlight before 5.1.40728 allow remote attackers to execute arbitrary code via a crafted TrueType font, aka "TrueType Font Parsing Vulnerability."
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Analysis
by VulDB Data Team • 06/08/2022
The CVE-2015-2435 vulnerability represents a critical heap-based buffer overflow in Microsoft's TrueType font parsing implementation that affects multiple operating systems and software products spanning from Windows Vista to Windows 10. This vulnerability specifically targets the Windows font subsystem's handling of malformed TrueType font files, creating a dangerous condition where remote attackers can craft malicious font files to execute arbitrary code on vulnerable systems. The flaw resides in the way Windows processes font data during rendering operations, particularly when parsing the font's metadata and glyph information structures. The vulnerability impacts not only core operating systems but also Office applications and communication platforms that rely on Windows font rendering capabilities, making it a widespread concern across enterprise environments where these technologies are deployed. This vulnerability aligns with CWE-121, heap-based buffer overflow, which occurs when a program writes data beyond the boundaries of a heap-allocated buffer, potentially allowing attackers to overwrite adjacent memory locations and execute malicious code. The attack vector is particularly concerning as it requires no user interaction beyond viewing or processing a malicious font file, making it a prime candidate for drive-by download attacks and automated exploitation campaigns.
The technical exploitation of CVE-2015-2435 involves attackers crafting specially designed TrueType font files that contain malformed data structures within the font's header and table entries. When a vulnerable system processes these malicious fonts, typically through normal font rendering operations in applications like Word, Excel, or web browsers, the parsing code fails to properly validate the font structure, leading to buffer overflow conditions. The vulnerability specifically affects the handling of font tables and their associated metadata, where the code attempts to copy font data into fixed-size buffers without adequate bounds checking. Attackers can leverage this flaw to overwrite critical memory locations including return addresses and function pointers, enabling them to redirect execution flow to malicious payloads. This type of exploitation aligns with the ATT&CK technique T1059.007 for command and scripting interpreter and T1203 for exploitation for privilege escalation, as the initial code execution often leads to further system compromise. The vulnerability is particularly dangerous in enterprise environments where users may encounter malicious fonts through email attachments, web downloads, or network shares, making it an attractive target for nation-state actors and advanced persistent threat groups who seek to establish persistent access to networked systems.
The operational impact of CVE-2015-2435 extends far beyond individual system compromise, affecting entire enterprise infrastructures due to the widespread deployment of vulnerable software across organizations. Organizations running affected versions of Windows, Office, or Lync products face significant risk of unauthorized access, data exfiltration, and system takeover when this vulnerability is exploited in the wild. The vulnerability's presence in both client and server operating systems means that attackers can target either endpoints or internal servers, creating multiple attack surfaces for exploitation. Security teams must consider the broad scope of affected products when planning mitigation strategies, as the vulnerability spans across multiple Microsoft product lines including Office suites, communication platforms, and various Windows versions. The exploitability of this vulnerability is enhanced by the fact that many organizations have not patched their systems, particularly in legacy environments where patch management processes are slow or non-existent. This creates a persistent threat landscape where attackers can leverage the vulnerability for extended periods without detection, potentially allowing for lateral movement and privilege escalation within compromised networks. The vulnerability's classification as a remote code execution flaw means that network-based attacks can be launched without requiring physical access to target systems, making it particularly dangerous for organizations with exposed network services or web applications that might process user-uploaded font files. Organizations should also consider the potential for zero-day exploitation of this vulnerability, as its widespread presence in deployed systems makes it a likely candidate for inclusion in advanced attack toolkits and exploit frameworks used by cybercriminals and threat actors.
Mitigation strategies for CVE-2015-2435 require comprehensive patch management across all affected Microsoft products and operating systems, with immediate priority given to Windows Vista, Windows 7, and Windows Server 2008 systems that have not received the relevant security updates. Microsoft released patches through Security Bulletin MS15-034 that addressed the vulnerability by implementing proper bounds checking in the font parsing routines and introducing additional validation mechanisms for font metadata structures. Organizations should also implement network-level protections including firewall rules that restrict access to font processing services and web applications that might be vulnerable to malicious font uploads. Application whitelisting solutions can provide additional defense-in-depth by restricting execution of unknown font processing applications and limiting the impact of potential exploitation attempts. System administrators should consider disabling unnecessary font rendering services and implementing strict file type validation for user-uploaded content to prevent automatic processing of potentially malicious font files. Regular vulnerability scanning and penetration testing should be conducted to identify systems that may not have received the required patches, particularly in legacy environments where patch deployment might be challenging. Organizations should also implement monitoring solutions that can detect unusual font processing activities or attempts to load malformed font files, as these activities may indicate exploitation attempts. The implementation of security awareness training for users can help reduce the risk of encountering malicious font files through email attachments or web downloads, while incident response procedures should be updated to address potential exploitation attempts involving this vulnerability. Given the historical nature of this vulnerability and its continued presence in unpatched systems, organizations should maintain continuous vigilance and regularly review their security postures to ensure comprehensive protection against this and similar font-based exploitation techniques.