CVE-2016-2801 in Firefox
Summary
by MITRE
The graphite2::TtfUtil::CmapSubtable12Lookup function in TtfUtil.cpp in Graphite 2 before 1.3.6, as used in Mozilla Firefox before 45.0 and Firefox ESR 38.x before 38.7, allows remote attackers to cause a denial of service (buffer over-read) or possibly have unspecified other impact via a crafted Graphite smart font, a different vulnerability than CVE-2016-2797.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-2801 represents a critical buffer over-read flaw within the Graphite 2 smart font rendering library, specifically affecting the graphite2::TtfUtil::CmapSubtable12Lookup function in TtfUtil.cpp. This issue impacts Mozilla Firefox versions prior to 45.0 and Firefox ESR 38.x versions prior to 38.7, creating a significant security risk for users of these affected browser versions. The flaw manifests when processing crafted Graphite smart fonts, which are sophisticated font formats designed to handle complex text rendering for various writing systems including those with complex ligatures, contextual shaping, and other advanced typographic features. The vulnerability stems from inadequate input validation and memory management within the font processing pipeline, where the application fails to properly bounds-check data structures during the parsing of cmap subtable 12 format mappings that are part of the TrueType font specification.
The technical exploitation of this vulnerability occurs through the manipulation of Graphite smart font files that contain maliciously crafted data within their cmap subtable 12 structures. When Firefox attempts to render text using such fonts, the TtfUtil::CmapSubtable12Lookup function processes the font data without sufficient validation, leading to a buffer over-read condition where the application attempts to access memory beyond the allocated buffer boundaries. This memory corruption can result in unpredictable behavior including application crashes, denial of service conditions, or potentially more severe consequences depending on the memory layout and exploitation circumstances. The vulnerability is classified as a buffer over-read according to CWE-121, which specifically addresses heap-based buffer overflow conditions where data is read beyond the allocated buffer limits, and it also relates to CWE-125, which covers out-of-bounds read vulnerabilities in memory management.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as the potential for unspecified other impacts suggests that attackers could leverage this condition to execute arbitrary code or gain additional privileges. The attack vector involves delivering a specially crafted Graphite smart font to a victim's system, which could occur through various means including malicious web content, email attachments, or other delivery mechanisms. When the vulnerable Firefox browser processes such content, the buffer over-read condition triggers, potentially allowing remote code execution or system compromise. This vulnerability is particularly concerning in the context of the ATT&CK framework, where it could be categorized under T1059 for command and scripting interpreter usage, T1070 for indicator removal on host, or T1190 for exploitation of remote services, depending on how attackers choose to leverage the initial compromise. The vulnerability affects the broader font rendering subsystem of Firefox, making it a high-value target for attackers seeking to exploit browser rendering engines.
Mitigation strategies for CVE-2016-2801 primarily focus on immediate software updates and patch management to ensure affected Firefox versions are upgraded to patched releases. Users should immediately update to Firefox 45.0 or later versions, or Firefox ESR 38.7 and later, which contain the necessary fixes for this vulnerability. Additionally, organizations should implement proactive monitoring and threat detection measures to identify potential exploitation attempts, particularly through the analysis of web traffic and content delivery patterns. Browser security hardening measures including sandboxing, content security policies, and restricted font loading capabilities can provide additional defense-in-depth layers. The vulnerability also highlights the importance of comprehensive input validation and memory safety practices in font rendering libraries, emphasizing the need for robust bounds checking and secure coding practices. Security teams should also consider implementing automated vulnerability scanning tools that can detect and alert on the presence of potentially malicious font files in web content or user environments, as the vulnerability can be exploited through various delivery mechanisms and requires continuous monitoring to prevent successful exploitation attempts.