CVE-2018-5101 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur when manipulating floating "first-letter" style elements, resulting in a potentially exploitable crash. This vulnerability affects Firefox < 58.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/30/2019
The vulnerability identified as CVE-2018-5101 represents a critical use-after-free flaw within the Mozilla Firefox browser that specifically manifests when handling floating first-letter style elements. This type of vulnerability falls under the broader category of memory safety issues and is classified as CWE-416, which encompasses use-after-free conditions where program memory is accessed after it has been freed. The flaw occurs in the rendering engine's handling of CSS properties that create floating elements, particularly those associated with the first-letter pseudo-element selector. When Firefox processes these specific CSS constructs, the browser fails to properly manage memory allocation and deallocation, creating opportunities for malicious actors to exploit the instability.
The technical implementation of this vulnerability involves the browser's CSS layout engine encountering a scenario where a memory region allocated for a floating first-letter element becomes freed while still being referenced by subsequent operations. This creates a race condition where the freed memory can be reallocated for other purposes, and if an attacker can control the content or structure of the CSS that triggers this condition, they can potentially execute arbitrary code. The vulnerability specifically affects Firefox versions prior to 58, indicating that this issue was present in the browser's rendering pipeline for several major releases. The exploitation mechanism typically requires crafting malicious CSS content that forces the browser into a state where it attempts to access memory that has already been freed, leading to unpredictable behavior that can be leveraged for code execution.
The operational impact of CVE-2018-5101 extends beyond simple browser instability, as it provides a potential pathway for remote code execution attacks. When exploited successfully, this vulnerability can allow attackers to execute arbitrary code with the privileges of the user running Firefox, potentially leading to complete system compromise. The vulnerability is particularly concerning because it affects the core rendering functionality of the browser, meaning that simply visiting a malicious website could trigger the exploit without requiring user interaction beyond normal browsing. This makes it a prime target for drive-by attacks and increases the attack surface significantly. The vulnerability demonstrates how seemingly benign CSS styling properties can become vectors for sophisticated exploitation techniques, highlighting the complexity of modern web browser security. Security researchers have mapped this vulnerability to ATT&CK technique T1059.007, which covers the use of scripting languages for execution, as the exploitation often involves JavaScript manipulation of CSS properties to trigger the memory corruption.
Mitigation strategies for CVE-2018-5101 primarily focus on immediate browser updates to versions 58 or later where the vulnerability has been patched. Mozilla released security updates that addressed the memory management issues in the CSS rendering engine, specifically fixing how floating first-letter elements are handled during layout calculations. Organizations should implement comprehensive patch management procedures to ensure all Firefox installations are updated promptly, as the vulnerability remains exploitable in older versions. Additional protective measures include implementing content security policies that limit the use of potentially dangerous CSS properties, using browser security extensions that can detect and block malicious content, and monitoring for suspicious network traffic patterns that may indicate exploitation attempts. The vulnerability serves as a reminder of the importance of memory safety in browser implementations and the need for continuous security auditing of web rendering engines. Security professionals should also consider implementing sandboxing mechanisms that limit the damage potential of any successful exploitation attempts, though the fundamental fix requires updating to patched browser versions. This vulnerability underscores the critical nature of keeping web browsers updated and the potential consequences of running outdated software in enterprise environments.