CVE-2017-7773 in Firefox
Summary
by MITRE
Heap-based Buffer Overflow write in Graphite2 library in Firefox before 54 in lz4::decompress src/Decompressor.
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Analysis
by VulDB Data Team • 05/29/2020
The vulnerability CVE-2017-7773 represents a critical heap-based buffer overflow within the Graphite2 library used by Mozilla Firefox browsers. This flaw exists in the lz4::decompress function within the src/Decompressor component of the Graphite2 library, which is employed by Firefox for processing font data and text rendering operations. The vulnerability specifically manifests when the browser encounters maliciously crafted font files that trigger improper memory handling during decompression processes.
The technical implementation of this vulnerability stems from inadequate bounds checking during the decompression of compressed font data. When Firefox processes font files that utilize the Graphite2 library for text rendering, the lz4::decompress function fails to properly validate the size of decompressed data against allocated memory buffers. This allows attackers to craft font files that, when processed by the vulnerable browser, cause the decompression routine to write beyond the bounds of allocated heap memory, resulting in a buffer overflow condition. The flaw operates at the intersection of font processing and compression algorithms, leveraging the complex interaction between the Graphite2 library and Firefox's rendering engine.
The operational impact of this vulnerability is severe and potentially exploitable for remote code execution attacks. An attacker could craft malicious font files that, when displayed in a web browser, trigger the buffer overflow condition and potentially allow arbitrary code execution on the victim's system. This creates a significant risk for users who browse the web with vulnerable Firefox versions, as the attack vector requires no user interaction beyond visiting a malicious website or opening a malicious document. The vulnerability affects Firefox versions prior to 54, making it particularly dangerous for users who have not updated their browsers. The heap-based nature of the overflow provides attackers with opportunities to manipulate memory layout and potentially achieve code execution through carefully crafted payloads.
Mitigation strategies for CVE-2017-7773 primarily focus on immediate browser updates to Firefox version 54 or later, which contains patches addressing the buffer overflow condition in the Graphite2 library. Organizations should implement comprehensive patch management procedures to ensure all Firefox installations are updated promptly. Additionally, browser security configurations can be enhanced through content security policies and sandboxing mechanisms that limit the potential impact of successful exploitation attempts. The vulnerability aligns with CWE-121, heap-based buffer overflow, and represents a typical example of how third-party libraries can introduce critical security flaws into complex software systems. Security professionals should monitor for similar vulnerabilities in font processing libraries and maintain awareness of the ATT&CK framework's techniques for exploitation of memory corruption vulnerabilities. Organizations should also consider implementing web application firewalls and network monitoring solutions that can detect and block malicious font content before it reaches vulnerable browsers.