CVE-2010-0421 in pango
Summary
by MITRE
Array index error in the hb_ot_layout_build_glyph_classes function in pango/opentype/hb-ot-layout.cc in Pango before 1.27.1 allows context-dependent attackers to cause a denial of service (application crash) via a crafted font file, related to building a synthetic Glyph Definition (aka GDEF) table by using this font's charmap and the Unicode property database.
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Analysis
by VulDB Data Team • 05/02/2026
The vulnerability identified as CVE-2010-0421 represents a critical array index error within the Pango text rendering library that affects versions prior to 1.27.1. This flaw exists in the hb_ot_layout_build_glyph_classes function located in pango/opentype/hb-ot-layout.cc, where improper handling of font data can lead to memory corruption and application instability. The vulnerability specifically manifests when processing crafted font files that contain malformed character mapping data, enabling attackers to exploit the library's handling of synthetic Glyph Definition tables during font processing operations.
The technical nature of this vulnerability stems from insufficient bounds checking during the construction of Glyph Definition tables, which are essential components of OpenType font formatting. When Pango attempts to build these synthetic tables by combining a font's character map with Unicode property database information, the array indexing logic fails to validate input parameters properly. This oversight creates a condition where maliciously constructed font files can trigger out-of-bounds memory access, leading to unpredictable behavior and potential application crashes. The flaw operates at the intersection of font parsing and layout engine functionality, making it particularly dangerous as it can be triggered during normal text rendering operations.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be leveraged to disrupt applications that rely on Pango for text rendering across multiple operating systems and software platforms. Attackers can craft specially formatted font files that, when processed by vulnerable applications, will cause the target software to crash or become unresponsive. This creates significant risks for desktop applications, web browsers, and any software that integrates Pango for typography handling. The context-dependent nature of the attack means that the vulnerability is most effectively exploited when applications process untrusted font data, such as user-uploaded fonts or fonts from unverified sources.
Security mitigations for this vulnerability primarily involve updating to Pango version 1.27.1 or later, which includes corrected bounds checking mechanisms in the hb_ot_layout_build_glyph_classes function. System administrators should prioritize patching affected applications that utilize vulnerable Pango libraries, particularly those handling user-supplied font content. Additional protective measures include implementing strict font validation policies, sandboxing font processing operations, and employing input sanitization techniques when handling font files from untrusted sources. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and can be classified under ATT&CK technique T1203 for process injection and T1059 for command and scripting interpreter usage in exploitation scenarios. Organizations should also consider monitoring for anomalous application behavior or crashes that may indicate exploitation attempts, as well as implementing network-based intrusion detection systems to identify potential malicious font file delivery attempts.