CVE-2016-2795 in Firefox
Summary
by MITRE
The graphite2::FileFace::get_table_fn function in Graphite 2 before 1.3.6, as used in Mozilla Firefox before 45.0 and Firefox ESR 38.x before 38.7, does not initialize memory for an unspecified data structure, which allows remote attackers to cause a denial of service or possibly have unknown 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-2016-2795 represents a critical memory initialization flaw within the Graphite 2 library implementation used by Mozilla Firefox and its extended support release versions. This issue specifically affects the graphite2::FileFace::get_table_fn function which handles font table retrieval operations for Graphite smart fonts. The flaw manifests when the function fails to properly initialize memory for an unspecified data structure, creating potential exploitation vectors for remote attackers. The vulnerability exists in Graphite 2 versions prior to 1.3.6 and impacts Firefox versions before 45.0 and Firefox ESR 38.x versions before 38.7, making it a significant concern for web browser security.
The technical nature of this vulnerability stems from improper memory management within the font processing subsystem, where uninitialized memory can contain residual data from previous operations or memory allocation patterns. When processing crafted Graphite smart fonts, the get_table_fn function does not adequately clear or initialize memory structures before use, potentially leading to information disclosure, arbitrary code execution, or denial of service conditions. This type of vulnerability falls under the CWE-457 category of "Use of Uninitialized Variable" and aligns with ATT&CK technique T1059.007 for execution through application-specific vulnerabilities. The uninitialized memory access creates unpredictable behavior that can be leveraged by attackers to manipulate program execution flow or extract sensitive information from memory.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it could potentially enable remote code execution in certain conditions. Attackers can craft malicious Graphite smart fonts that trigger the uninitialized memory access when processed by affected browsers, leading to system compromise or data exposure. The vulnerability affects web browsing environments where smart fonts are rendered, making it particularly dangerous in scenarios involving untrusted content delivery. This flaw demonstrates the critical importance of proper memory initialization in font rendering libraries, as font processing represents a common attack surface for browser exploitation. The vulnerability's impact is amplified by the widespread use of Graphite smart fonts in various web applications and document formats, creating numerous potential attack vectors for malicious actors.
Mitigation strategies for CVE-2016-2795 require immediate patching of affected software versions to upgrade to Graphite 2.1.3.6 or later, and to ensure Firefox browsers are updated to versions 45.0 or later for main releases and 38.7 for extended support releases. Organizations should implement network-level protections such as content filtering and web application firewalls to prevent delivery of malicious font files. Security teams should also consider disabling Graphite font support in browser configurations where it is not essential for functionality. The fix addresses the root cause by ensuring proper memory initialization before font table processing operations, eliminating the potential for uninitialized memory access. Regular security audits of font processing libraries and browser components should be conducted to identify similar memory management issues that could present similar attack vectors. This vulnerability underscores the necessity of thorough memory management practices in font rendering engines and highlights the importance of maintaining updated software components to prevent exploitation of such fundamental security flaws.