CVE-2016-2802 in Firefox
Summary
by MITRE
The graphite2::TtfUtil::CmapSubtable4NextCodepoint 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-2016-2802 represents a critical buffer over-read flaw within the Graphite 2 smart font handling component that affected major web browsers including Mozilla Firefox and its extended support release versions. This issue resides in the graphite2::TtfUtil::CmapSubtable4NextCodepoint function, which processes cmap subtable 4 data structures within font files. The flaw manifests when browsers encounter specially crafted Graphite smart fonts that contain malformed or oversized data structures, leading to memory access violations that can compromise system stability.
The technical exploitation of this vulnerability occurs through the manipulation of font rendering processes where the Graphite 2 library fails to properly validate input data from cmap subtable 4 structures. When Firefox attempts to process these malicious fonts, the CmapSubtable4NextCodepoint function reads beyond allocated memory boundaries, resulting in unpredictable behavior. This type of buffer over-read vulnerability maps to CWE-125 in the Common Weakness Enumeration catalog, which specifically addresses out-of-bounds read conditions that can lead to denial of service or information disclosure. The vulnerability demonstrates characteristics consistent with the attack pattern described in MITRE ATT&CK technique T1059.007 for execution through web browsers, where malicious code execution is achieved through crafted input data.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as the buffer over-read condition can potentially lead to arbitrary code execution in memory space. Attackers can leverage this flaw by hosting malicious Graphite smart fonts on web servers that users might visit, triggering the vulnerability during normal font rendering operations. This creates a significant risk for web-based attacks where remote code execution becomes possible, particularly when combined with other browser vulnerabilities in the exploitation chain. The vulnerability affects not only the targeted browser but also any application that utilizes the affected Graphite 2 library for font processing, making it a widespread concern across various software ecosystems that depend on smart font rendering capabilities.
Mitigation strategies for CVE-2016-2802 primarily involve immediate patching of affected software versions, with Mozilla releasing Firefox 45.0 and Firefox ESR 38.7 to address the issue. System administrators should ensure all instances of affected browsers are updated to patched versions, while developers should implement proper input validation and bounds checking in their font processing libraries. Additional protective measures include implementing content security policies that restrict font loading from untrusted sources and employing sandboxing techniques to isolate font rendering processes. The vulnerability highlights the importance of robust memory safety practices in font processing libraries and demonstrates the critical need for regular security updates in widely deployed software components. Organizations should also consider implementing network-based intrusion detection systems that can identify attempts to serve malicious font content, as well as monitoring for unusual browser behavior that might indicate exploitation attempts.