CVE-2016-1969 in Firefox
Summary
by MITRE
The setAttr function in Graphite 2 before 1.3.6, as used in Mozilla Firefox before 45.0 and Firefox ESR 38.x before 38.6.1, allows remote attackers to cause a denial of service (out-of-bounds write) or possibly have unspecified other impact via a crafted Graphite smart font.
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Analysis
by VulDB Data Team • 10/11/2024
The vulnerability identified as CVE-2016-1969 represents a critical out-of-bounds write flaw within the Graphite 2 font processing library, which was extensively utilized by Mozilla Firefox and its extended support release versions. This vulnerability specifically affects the setAttr function within Graphite 2 versions prior to 1.3.6, creating a pathway for remote attackers to exploit the system through carefully crafted smart fonts. The flaw manifests when the Graphite 2 library processes Graphite smart fonts, which are advanced font formats that contain sophisticated layout instructions and character shaping rules. These smart fonts are designed to handle complex text rendering for languages with intricate writing systems such as Arabic, Indic scripts, and other complex scripts that require sophisticated typographic handling.
The technical nature of this vulnerability stems from insufficient bounds checking within the setAttr function, which is responsible for setting attributes of font glyphs during the text rendering process. When a maliciously crafted Graphite smart font is processed by the vulnerable Firefox version, the function fails to properly validate input data boundaries, leading to memory corruption that can result in arbitrary code execution or complete application crash. This type of vulnerability falls under the CWE-121 category of Stack-based Buffer Overflow, though it specifically manifests as an out-of-bounds write condition that can be exploited through heap memory corruption patterns. The vulnerability is particularly dangerous because it operates at the font rendering layer, which is frequently accessed during web browsing operations, making it an ideal target for drive-by attacks.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially enable remote code execution on affected systems. Attackers can craft Graphite smart fonts that, when loaded by a vulnerable Firefox browser, trigger the out-of-bounds write condition and subsequently allow arbitrary code execution with the privileges of the browser process. This represents a significant threat to user security, as it can be exploited through various attack vectors including malicious websites, email attachments, or any content that triggers font rendering. The vulnerability's exploitation aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as successful exploitation could lead to full system compromise. The attack surface is particularly broad since font rendering is a fundamental browser operation that occurs frequently during web browsing, making this vulnerability highly attractive to threat actors.
Mitigation strategies for this vulnerability primarily focus on immediate patching of affected software versions, with Mozilla recommending users upgrade to Firefox 45.0 or later versions and Firefox ESR 38.6.1 or later. System administrators should prioritize updating the Graphite 2 library to version 1.3.6 or higher, which contains the necessary bounds checking fixes. Additional protective measures include implementing content security policies that restrict font loading from untrusted sources, enabling sandboxing features within the browser, and deploying network-based intrusion detection systems that can identify and block malicious font content. Organizations should also consider implementing browser hardening techniques such as disabling Graphite font support entirely if the functionality is not required for business operations, though this may impact rendering quality for certain international scripts. The vulnerability serves as a reminder of the importance of font security in modern web browsers and the need for comprehensive input validation across all font processing libraries to prevent similar issues in the future.