CVE-2016-2791 in Firefox
Summary
by MITRE
The graphite2::GlyphCache::glyph 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-2016-2791 represents a critical buffer over-read flaw within the Graphite 2 font rendering library that affected major web browsers including Mozilla Firefox. This issue stems from inadequate input validation within the graphite2::GlyphCache::glyph function, which processes smart fonts that contain advanced typographic information. The flaw specifically manifests when the library attempts to cache glyph data for complex font rendering operations, creating a scenario where maliciously crafted font files can trigger memory access violations.
The technical implementation of this vulnerability occurs through the manipulation of Graphite smart font structures that contain embedded typographic rules and glyph positioning data. When Firefox processes these specially crafted fonts, the graphite2::GlyphCache::glyph function fails to properly bounds-check array accesses during glyph caching operations, leading to memory corruption. This buffer over-read condition allows attackers to read data beyond the allocated memory boundaries, potentially exposing sensitive information from adjacent memory locations or causing the application to crash.
From an operational perspective, this vulnerability poses significant risks to web browser security and stability. Remote attackers can exploit this flaw by hosting maliciously crafted Graphite smart fonts on web servers, which then get rendered when users visit compromised websites. The impact extends beyond simple denial of service, as the buffer over-read could potentially be leveraged to execute arbitrary code or expose confidential data, making it particularly dangerous in the context of browser-based attacks. The vulnerability affects both regular Firefox releases and the extended support releases, indicating its widespread impact across different browser versions.
The mitigation strategies for CVE-2016-2791 primarily focus on software updates and library patches that address the underlying buffer over-read condition in Graphite 2. Mozilla released versions 45.0 and 38.7 to resolve this issue, incorporating updated Graphite 2 libraries with proper bounds checking mechanisms. Security professionals should prioritize patching affected systems and implementing monitoring for suspicious font loading activities. This vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and maps to ATT&CK technique T1059.007 for execution through web-based attacks. Organizations should also consider implementing web content filtering solutions that can detect and block known malicious font files, while maintaining awareness of similar font rendering vulnerabilities that may exist in other software components.