CVE-2017-7776 in Firefox
Summary
by MITRE
Heap-based Buffer Overflow read in Graphite2 library in Firefox before 54 in graphite2::Silf::getClassGlyph.
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Analysis
by VulDB Data Team • 05/29/2020
The vulnerability CVE-2017-7776 represents a critical heap-based buffer overflow within the Graphite2 library implementation in Mozilla Firefox versions prior to 54. This flaw specifically manifests in the graphite2::Silf::getClassGlyph function where improper input validation leads to memory corruption during font processing operations. The Graphite2 library serves as a core component for advanced text layout and rendering in Firefox, particularly handling complex scripts and font features that require sophisticated typographic processing. When maliciously crafted font data is processed through this vulnerable function, the buffer overflow occurs in heap memory allocation, potentially allowing remote attackers to execute arbitrary code with the privileges of the user running Firefox.
The technical exploitation of this vulnerability occurs through the manipulation of font files that contain specially crafted glyph data within the Graphite2 font processing pipeline. The flaw stems from inadequate bounds checking in the getClassGlyph method where the library fails to properly validate the size of incoming data before copying it into fixed-size buffers. This type of vulnerability falls under CWE-121, heap-based buffer overflow, which is classified as a critical security weakness in memory management. The attack vector typically involves a malicious website or document containing crafted font data that triggers the vulnerable code path when Firefox attempts to render text using the affected font processing engine. The vulnerability is particularly dangerous because it can be exploited remotely through web content without requiring user interaction beyond visiting a malicious webpage.
The operational impact of this vulnerability extends beyond simple code execution to encompass complete system compromise when exploited successfully. Attackers can leverage this buffer overflow to gain arbitrary code execution within the Firefox process context, potentially leading to full system compromise depending on the user's privilege level. The vulnerability affects all Firefox versions prior to 54, making it particularly concerning for organizations that have not yet updated their browser installations. The Graphite2 library's role in handling complex text rendering means that the attack surface is broad, as any webpage or document utilizing fonts that trigger this code path could serve as an attack vector. This vulnerability also aligns with ATT&CK technique T1059.007, which describes the use of scripting languages and command-line interfaces, as the exploitation could potentially involve command injection within the browser process.
Organizations and users should prioritize immediate patching of Firefox installations to version 54 or later, which contains the necessary fixes for this vulnerability. The mitigation strategy involves not only updating the browser but also implementing network-level protections such as web application firewalls that can detect and block malicious font content. Additional defensive measures include disabling complex font rendering features when possible, implementing strict content filtering policies, and monitoring for unusual memory allocation patterns that might indicate exploitation attempts. Security teams should also consider implementing browser hardening measures such as address space layout randomization and stack canaries to make exploitation more difficult. The vulnerability serves as a reminder of the critical importance of keeping font processing libraries up to date, as these components often handle untrusted input from web content and represent significant attack surfaces in modern browsers.