CVE-2016-2799 in Firefox
Summary
by MITRE
Heap-based buffer overflow in the graphite2::Slot::setAttr 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 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-2016-2799 represents a critical heap-based buffer overflow within the graphite2::Slot::setAttr function of the Graphite 2 library version 1.3.5 and earlier. This flaw exists in the font rendering subsystem that processes Graphite smart fonts, which are advanced typography fonts capable of handling complex writing systems and language-specific rendering rules. The vulnerability specifically affects Mozilla Firefox versions prior to 45.0 and Firefox ESR 38.x versions prior to 38.7, making it a significant concern for web browser security. Graphite smart fonts are designed to support complex scripts such as Arabic, Indic, and other non-Latin writing systems that require sophisticated rendering algorithms, which makes this vulnerability particularly dangerous as it could be exploited through web content that utilizes such fonts.
The technical nature of this vulnerability stems from improper bounds checking within the graphite2::Slot::setAttr function, which handles attribute setting for font slots during text rendering operations. When a malicious Graphite smart font is processed by the vulnerable Firefox browser, the function fails to validate the size of data being written to heap memory, allowing an attacker to write beyond allocated buffer boundaries. This heap corruption can result in memory corruption that manifests as unpredictable behavior, application crashes, or potentially more severe consequences depending on the execution environment. The vulnerability operates at the intersection of font processing and memory management, where input validation fails to account for maliciously crafted font data that could cause memory corruption patterns leading to denial of service or potential code execution.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as the heap-based nature of the overflow creates opportunities for more sophisticated exploitation techniques. Attackers could potentially craft malicious Graphite smart fonts that, when rendered by vulnerable browsers, could cause memory corruption leading to arbitrary code execution or complete browser compromise. The vulnerability affects web content delivery systems where Graphite fonts might be used for typography, particularly in internationalized web applications or websites serving content in complex scripts. Security researchers have classified this vulnerability as having potential for remote code execution, making it a high-risk issue for web browser vendors and users who may encounter malicious content through standard web browsing activities.
Mitigation strategies for CVE-2016-2799 primarily focus on updating affected software to patched versions of the Graphite 2 library and Mozilla Firefox browsers. The recommended approach involves upgrading to Firefox 45.0 or later versions and Firefox ESR 38.7 or later, which include fixes for the buffer overflow issue in the graphite2 library. Organizations should also implement content filtering measures to restrict the use of Graphite smart fonts in environments where such fonts are not essential, particularly in high-security contexts where the risk of exploitation is elevated. The vulnerability aligns with CWE-121, heap-based buffer overflow, and may map to ATT&CK technique T1059.007 for remote code execution through browser-based attacks, emphasizing the importance of keeping font rendering libraries updated as part of comprehensive security maintenance programs. System administrators should prioritize patch management for this vulnerability due to its potential for remote exploitation and the widespread use of affected browser versions in enterprise environments.