CVE-2016-2798 in Firefox
Summary
by MITRE
The graphite2::GlyphCache::Loader::Loader function 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.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-2798 represents a critical buffer over-read flaw within the Graphite 2 smart font rendering library that was extensively utilized by Mozilla Firefox and its extended support release versions. This issue specifically targets the graphite2::GlyphCache::Loader::Loader function which processes Graphite smart fonts, creating a potential attack surface for remote adversaries seeking to exploit the browser's font handling capabilities. The vulnerability exists in Graphite 2 versions prior to 1.3.6 and affects Firefox versions before 45.0 and Firefox ESR 38.x versions before 38.7, indicating a widespread impact across multiple browser release channels and support cycles.
The technical nature of this flaw stems from inadequate input validation within the font rendering pipeline where the Loader function fails to properly bounds-check glyph data when processing crafted Graphite smart fonts. When a maliciously constructed font file is processed by the vulnerable browser, the function attempts to read beyond allocated memory boundaries, resulting in a buffer over-read condition that can trigger memory corruption. This type of vulnerability falls under the CWE-121 category of stack-based buffer overflow, though the specific implementation manifests as a buffer over-read rather than a traditional stack overflow. The flaw operates at the intersection of font rendering and memory management, where the parsing logic does not adequately validate the size or structure of incoming font data before attempting to access memory locations.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as the buffer over-read condition could potentially be leveraged to execute arbitrary code or cause more severe system instability. Remote attackers can craft Graphite smart fonts that, when loaded by vulnerable browsers, trigger the over-read condition and potentially lead to unpredictable behavior including crashes, memory corruption, or in more sophisticated attack scenarios, code execution within the browser process context. This vulnerability directly relates to the ATT&CK technique T1059.007 for Command and Scripting Interpreter and T1203 for Exploitation for Client Execution, as it provides an attack vector for remote code execution through font processing. The exploitation potential is particularly concerning given that Graphite smart fonts are commonly used in web content, making this a prevalent attack surface for remote exploitation.
Mitigation strategies for CVE-2016-2798 focus primarily on updating to patched versions of both the Graphite 2 library and affected Firefox releases. Organizations should prioritize immediate deployment of Firefox 45.0 or later versions and Firefox ESR 38.7 or later, along with updating the underlying Graphite 2 library to version 1.3.6 or higher. Additional defensive measures include implementing content security policies that restrict font loading from untrusted sources, deploying web application firewalls that can detect and block malicious font files, and utilizing sandboxing techniques that limit the potential impact of successful exploitation attempts. Network-level protections such as DNS filtering and web content filtering solutions can also help prevent users from accessing malicious font files hosted on compromised websites. The vulnerability highlights the importance of font security in web browsers and demonstrates how seemingly benign components like font rendering can become critical attack vectors requiring continuous security monitoring and patch management processes.