CVE-2015-8947 in HarfBuzz
Summary
by MITRE
hb-ot-layout-gpos-table.hh in HarfBuzz before 1.0.5 allows remote attackers to cause a denial of service (buffer over-read) or possibly have unspecified other impact via crafted data, a different vulnerability than CVE-2016-2052.
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Analysis
by VulDB Data Team • 09/09/2022
The vulnerability identified as CVE-2015-8947 affects HarfBuzz version 1.0.4 and earlier, specifically within the hb-ot-layout-gpos-table.hh component that handles OpenType font layout operations. This flaw represents a classic buffer over-read condition that occurs when processing maliciously crafted font data, making it particularly dangerous in environments where untrusted font content is processed. The vulnerability stems from insufficient input validation and bounds checking within the font table parsing logic, allowing attackers to manipulate memory access patterns through carefully constructed font files.
The technical implementation of this vulnerability resides in the Glyph Positioning (GPOS) table processing logic where HarfBuzz attempts to parse and interpret font positioning data. When encountering malformed or crafted data within the GPOS table structure, the parsing routine fails to properly validate array indices or buffer boundaries before accessing memory locations. This allows attackers to craft font files that cause the application to read beyond allocated memory regions, potentially leading to denial of service conditions or more severe consequences depending on the execution environment. The flaw operates at the intersection of font rendering and memory management, leveraging the complex data structures used in OpenType font specifications to achieve its malicious effects.
The operational impact of CVE-2015-8947 extends beyond simple denial of service scenarios, as the vulnerability could potentially enable arbitrary code execution in certain contexts where the over-read behavior can be chained with other memory corruption issues. Systems utilizing HarfBuzz for font rendering across web browsers, desktop applications, or server-side font processing are particularly vulnerable. The attack surface includes any application that processes untrusted font content, such as email clients handling embedded fonts, web browsers rendering web pages with custom fonts, or document processing systems that convert or display font-based content. This vulnerability demonstrates the critical security implications of font processing libraries in modern computing environments where font rendering is increasingly integrated into core application functionality.
Organizations should implement immediate mitigations including updating to HarfBuzz version 1.0.5 or later, which contains the necessary patches to address the buffer over-read condition. Additionally, deployment of input validation measures and sandboxing techniques for font processing operations can provide additional defense layers. The vulnerability aligns with CWE-129, which describes improper validation of array indices, and relates to ATT&CK technique T1059.007 for execution through web browsers and T1203 for exploitation of input validation weaknesses. Security monitoring should focus on identifying unusual font processing patterns and memory access violations, while network segmentation can help limit the potential impact of successful exploitation attempts. Regular security assessments of font rendering components and comprehensive patch management programs are essential for maintaining system integrity against similar vulnerabilities in font processing libraries.