CVE-2018-5159 in Firefox
Summary
by MITRE
An integer overflow can occur in the Skia library due to 32-bit integer use in an array without integer overflow checks, resulting in possible out-of-bounds writes. This could lead to a potentially exploitable crash triggerable by web content. This vulnerability affects Thunderbird < 52.8, Thunderbird ESR < 52.8, Firefox < 60, and Firefox ESR < 52.8.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2018-5159 represents a critical integer overflow condition within the Skia graphics library that forms a foundational component of Mozilla's browser architecture. This flaw manifests when 32-bit integers are employed in array indexing operations without proper overflow validation mechanisms, creating a scenario where maliciously crafted web content can manipulate memory access patterns. The Skia library serves as Mozilla's 2D graphics rendering engine, processing various graphical elements including images, vector graphics, and text rendering operations that are fundamental to web browsing experiences. When the integer overflow occurs during array boundary calculations, it can result in out-of-bounds memory writes that may corrupt adjacent memory locations and potentially allow remote code execution.
The technical implementation of this vulnerability stems from improper input validation within the Skia graphics processing pipeline where integer variables representing array indices or sizes are not adequately checked for overflow conditions before being used in memory allocation or access operations. This type of flaw aligns with CWE-190, which specifically addresses integer overflow conditions that can lead to memory corruption and arbitrary code execution. The vulnerability is particularly concerning because it operates at the graphics rendering layer, where web content can trigger the problematic code path through seemingly benign operations such as image processing or canvas drawing commands. Attackers can exploit this by crafting malicious web pages that contain specially formatted graphics data or HTML elements that, when rendered by the browser, cause the Skia library to perform the integer overflow operation.
The operational impact of CVE-2018-5159 extends beyond simple browser crashes to potentially enable full remote code execution capabilities. When the integer overflow leads to out-of-bounds writes, the corrupted memory can overwrite critical program structures, function pointers, or return addresses, allowing attackers to redirect execution flow and inject malicious code. This vulnerability affects multiple Mozilla products including Firefox and Thunderbird across their respective versions, with specific impacts on versions prior to 52.8 for Thunderbird ESR and 52.8 for Thunderbird, as well as Firefox versions before 60 and Firefox ESR before 52.8. The vulnerability's exploitation potential is further amplified by its location within the graphics rendering pipeline, which is frequently accessed when browsing modern web pages that contain rich media content, making it highly relevant to real-world attack scenarios.
Organizations and users affected by this vulnerability should prioritize immediate patching of their browser installations to address the integer overflow condition in the Skia library. The recommended mitigation strategy involves updating to the patched versions of Firefox and Thunderbird that contain fixes for the specific integer overflow handling in the graphics rendering components. Security teams should also implement network-level controls to monitor for suspicious web content patterns and consider deploying web application firewalls that can detect and block potentially malicious graphics data. From an ATT&CK framework perspective, this vulnerability maps to techniques involving memory corruption and code execution, specifically aligning with T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation. The vulnerability demonstrates how low-level library flaws can create high-impact security risks that affect entire software ecosystems, emphasizing the critical importance of proper integer overflow checking in security-critical components and the need for comprehensive security testing of graphics rendering libraries.