CVE-2016-1523 in Graphite
Summary
by MITRE
The SillMap::readFace function in FeatureMap.cpp in Libgraphite in Graphite 2 1.2.4, as used in Mozilla Firefox before 43.0 and Firefox ESR 38.x before 38.6.1, mishandles a return value, which allows remote attackers to cause a denial of service (missing initialization, NULL pointer dereference, and application crash) via a crafted Graphite smart font.
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Analysis
by VulDB Data Team • 10/23/2024
The vulnerability identified as CVE-2016-1523 represents a critical flaw in the Graphite smart font rendering system within Mozilla Firefox browsers. This issue resides in the SillMap::readFace function located within FeatureMap.cpp of the Libgraphite library version 2.1.2.4, which serves as the underlying font processing engine for Graphite smart fonts. The vulnerability manifests when Firefox processes specially crafted Graphite fonts that exploit improper handling of return values during the font parsing process.
The technical nature of this vulnerability stems from a missing initialization error that leads to a NULL pointer dereference condition. When the SillMap::readFace function processes maliciously constructed Graphite font data, it fails to properly validate or initialize critical memory references before attempting to access them. This flaw falls under the CWE-476 category of NULL Pointer Dereference, where the application attempts to access memory through a pointer that has not been properly initialized or has been set to NULL. The improper return value handling creates a scenario where the application continues execution with invalid memory references, ultimately resulting in application crashes.
The operational impact of this vulnerability is significant as it enables remote attackers to execute a denial of service attack against Firefox users. Attackers can craft malicious Graphite smart fonts that, when rendered by Firefox, trigger the NULL pointer dereference and subsequent application crash. This vulnerability affects Firefox versions prior to 43.0 and Firefox ESR 38.x versions prior to 38.6.1, representing a substantial user base that would be exposed to this attack vector. The attack requires no user interaction beyond visiting a webpage containing the malicious font, making it particularly dangerous as it can be exploited through web-based attacks.
From an adversary perspective, this vulnerability aligns with ATT&CK technique T1203 - Exploitation for Client Execution, where attackers leverage application vulnerabilities to execute malicious code or cause system instability. The vulnerability's exploitation pathway follows the typical remote code execution attack pattern where a crafted input triggers a memory corruption issue. The specific ATT&CK matrix mapping indicates this vulnerability could be leveraged in conjunction with other techniques such as T1059 - Command and Scripting Interpreter, where the application crash could potentially be used as a stepping stone for more sophisticated attacks.
Mitigation strategies for this vulnerability primarily involve immediate software updates to the patched versions of Firefox. Users should upgrade to Firefox 43.0 or later versions, or Firefox ESR 38.6.1 and later, which contain the necessary patches to address the return value handling issue in the SillMap::readFace function. Additionally, administrators can implement content filtering measures to restrict the loading of Graphite smart fonts from untrusted sources, though this approach may impact legitimate font rendering functionality. Security monitoring should include detection of unusual application crash patterns that might indicate exploitation attempts, particularly in environments where users encounter untrusted web content. The vulnerability demonstrates the importance of proper input validation and error handling in font processing libraries, emphasizing the need for comprehensive testing of edge cases in font rendering systems.