CVE-2016-2800 in Firefox
Summary
by MITRE
The graphite2::Slot::getAttr function in Slot.cpp 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, a different vulnerability than CVE-2016-2792.
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Analysis
by VulDB Data Team • 07/09/2022
The vulnerability identified as CVE-2016-2800 represents a critical buffer over-read flaw within the Graphite 2 text rendering library, specifically affecting the graphite2::Slot::getAttr function in Slot.cpp. This vulnerability exists in Graphite 2 versions prior to 1.3.6 and has significant implications for web browsers that utilize this library for smart font rendering. The issue manifests when processing crafted Graphite smart fonts, which are advanced font formats that contain complex typographic instructions and layout information. These smart fonts are designed to handle sophisticated text rendering operations including complex scripts, ligatures, and contextual substitutions that traditional fonts cannot manage effectively.
The technical exploitation of this vulnerability occurs through improper bounds checking within the getAttr function, which fails to validate the size of data structures before accessing memory locations. When a maliciously crafted Graphite smart font is processed, the function attempts to read beyond the allocated buffer boundaries, leading to unpredictable behavior. This buffer over-read condition can result in memory corruption that manifests as denial of service conditions where the application crashes or becomes unresponsive. The vulnerability is particularly dangerous because it operates at the font rendering layer, which is frequently accessed when displaying web content, making it an attractive target for remote attackers who can craft malicious web pages to exploit this weakness.
The operational impact of CVE-2016-2800 extends beyond simple denial of service scenarios, as the buffer over-read condition may potentially allow for more severe consequences including arbitrary code execution. Attackers can leverage this vulnerability by hosting malicious web content that forces vulnerable browsers to process the crafted smart font, leading to system compromise. This vulnerability affects Mozilla Firefox versions before 45.0 and Firefox ESR 38.x versions before 38.7, representing a substantial portion of the browser user base at the time of discovery. The flaw demonstrates poor input validation practices and highlights the importance of robust memory management in font rendering libraries that handle complex data structures.
Security researchers have classified this vulnerability under CWE-125, which specifically addresses "Out-of-bounds Read" conditions, and it aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript', as the exploitation often occurs through web-based attack vectors. The vulnerability's impact is amplified by its location within the core rendering pipeline, making it particularly effective for remote code execution attacks. Organizations affected by this vulnerability must prioritize immediate patching of their Firefox installations to prevent potential exploitation, as the attack surface includes any web content that might utilize Graphite smart fonts. The remediation process requires updating to Graphite 2 version 1.3.6 or later, which includes proper bounds checking mechanisms and improved memory management to prevent the over-read conditions that enable exploitation.
This vulnerability serves as a critical reminder of the security risks associated with complex font rendering systems and the importance of thorough input validation in all components of web browsers. The flaw represents a classic example of how seemingly benign functionality can become a security liability when proper bounds checking is not implemented, particularly in systems that process untrusted data from the internet. The vulnerability's classification as a remote attack vector means that users can be compromised without any interaction beyond visiting a malicious website, making it particularly dangerous in enterprise environments where web browsing is a daily activity. Security teams should implement network monitoring to detect potential exploitation attempts and ensure that all systems are updated to versions that include the necessary patches to address this buffer over-read vulnerability.