CVE-2015-9274 in HarfBuzz
Summary
by MITRE
HarfBuzz before 1.0.4 allows remote attackers to cause a denial of service (invalid read of two bytes and application crash) because of GPOS and GSUB table mishandling, related to hb-ot-layout-gpos-table.hh, hb-ot-layout-gsub-table.hh, and hb-ot-layout-gsubgpos-private.hh.
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Analysis
by VulDB Data Team • 06/06/2023
The vulnerability identified as CVE-2015-9274 represents a critical denial of service flaw affecting HarfBuzz version 1.0.3 and earlier, which is a crucial text shaping library used extensively in modern operating systems and applications for proper text rendering. This vulnerability specifically targets the OpenType font layout tables GPOS and GSUB, which are fundamental components responsible for advanced typographic features such as kerning, ligatures, and glyph substitution. The flaw exists in the hb-ot-layout-gpos-table.hh, hb-ot-layout-gsub-table.hh, and hb-ot-layout-gsubgpos-private.hh files, which handle the parsing and processing of these font tables during text rendering operations.
The technical exploitation of this vulnerability occurs when malformed or maliciously crafted OpenType font files are processed by applications utilizing HarfBuzz for text rendering. The flaw manifests as an invalid read of two bytes followed by an application crash, indicating that the library fails to properly validate input data within the GPOS and GSUB table structures. This improper handling leads to memory access violations that cause the application to terminate unexpectedly, effectively creating a denial of service condition. The vulnerability stems from insufficient bounds checking and input validation within the font table parsing logic, where the library attempts to read data beyond the allocated buffer boundaries when processing malformed table entries.
From an operational perspective, this vulnerability poses significant risks to systems that rely on HarfBuzz for text processing, including web browsers, office suites, desktop environments, and mobile applications. The impact extends beyond simple application crashes to potentially affect entire user sessions or system stability, particularly in environments where font rendering is critical for user interface functionality. Attackers can exploit this vulnerability by delivering malicious font files through various attack vectors such as email attachments, web pages, or file sharing systems, making it particularly dangerous in enterprise and cloud environments where automated font processing may occur without user intervention. The vulnerability's classification aligns with CWE-125, which describes out-of-bounds read conditions, and can be mapped to ATT&CK technique T1203, specifically targeting application vulnerabilities through malicious file delivery.
The recommended mitigations for CVE-2015-9274 include immediate upgrading to HarfBuzz version 1.0.4 or later, which contains the necessary patches to address the improper table handling logic. System administrators should also implement proper input validation and sanitization for font files, particularly in environments where user-uploaded content is processed. Additionally, organizations should consider implementing network-level controls to restrict access to potentially malicious font files and ensure that applications using HarfBuzz are running with appropriate memory protection mechanisms. The fix addresses the root cause by implementing proper bounds checking and input validation within the GPOS and GSUB table processing functions, preventing the invalid memory reads that previously led to application crashes and system instability.