CVE-2017-7771 in Firefox
Summary
by MITRE
Out-of-bounds read in Graphite2 Library in Firefox before 54 in graphite2::Pass::readPass function.
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Analysis
by VulDB Data Team • 05/29/2020
The vulnerability CVE-2017-7771 represents a critical out-of-bounds read flaw within the Graphite2 library implementation in Mozilla Firefox versions prior to 54. This issue manifests specifically within the graphite2::Pass::readPass function, where improper input validation allows attackers to manipulate memory access patterns. The Graphite2 library serves as a complex text rendering engine that handles advanced typography and font processing for various writing systems, making it a critical component in Firefox's rendering pipeline. When exploited, this vulnerability enables attackers to read memory locations beyond the intended buffer boundaries, potentially exposing sensitive data or enabling further exploitation techniques.
The technical implementation of this flaw involves the graphite2::Pass::readPass function failing to properly validate input parameters before processing font data. This function is responsible for parsing and interpreting Graphite2 font tables that contain complex typographic information including glyph positioning, kerning data, and contextual substitution rules. Attackers can craft malicious font files that contain specially formatted data structures designed to trigger the out-of-bounds memory access when Firefox attempts to render text using these fonts. The vulnerability stems from inadequate bounds checking mechanisms that should validate the size and structure of font data before processing, allowing arbitrary memory reads that can be leveraged for information disclosure or code execution.
The operational impact of CVE-2017-7771 extends beyond simple information disclosure, as it represents a significant security risk that can be exploited in various attack scenarios. The vulnerability can be triggered through malicious web content, particularly when users visit compromised websites or download malicious documents containing crafted font files. This makes it particularly dangerous in phishing campaigns or drive-by download attacks where attackers can leverage the vulnerability to extract sensitive information from the victim's system. The flaw's classification as a remote code execution vector through information disclosure demonstrates how seemingly benign memory access issues can be escalated into more severe security threats, potentially allowing attackers to bypass modern security mitigations such as address space layout randomization and data execution protection.
Mitigation strategies for CVE-2017-7771 primarily focus on immediate patch deployment and browser updates, as this vulnerability was addressed through Firefox version 54 and subsequent releases. Organizations should prioritize updating all affected Firefox installations to versions containing the patched Graphite2 library implementation. Additionally, implementing network-level protections such as content filtering and web application firewalls can provide additional defense-in-depth measures. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and can be mapped to ATT&CK technique T1059 for execution through malicious web content. Security teams should also consider implementing monitoring for unusual memory access patterns and network traffic related to font rendering operations, as these activities may indicate exploitation attempts. Regular security assessments of font handling capabilities and comprehensive vulnerability scanning of web applications that process user-uploaded content are essential practices to prevent exploitation of similar rendering engine vulnerabilities.