CVE-2016-5127 in Chrome
Summary
by MITRE
Use-after-free vulnerability in WebKit/Source/core/editing/VisibleUnits.cpp in Blink, as used in Google Chrome before 52.0.2743.82, allows remote attackers to cause a denial of service or possibly have unspecified other impact via crafted JavaScript code involving an @import at-rule in a Cascading Style Sheets (CSS) token sequence in conjunction with a rel=import attribute of a LINK element.
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Analysis
by VulDB Data Team • 09/09/2022
The CVE-2016-5127 vulnerability represents a critical use-after-free flaw within the Blink rendering engine's WebKit implementation that affected Google Chrome versions prior to 52.0.2743.82. This vulnerability resides in the VisibleUnits.cpp file within the core editing module, specifically manifesting when processing CSS token sequences containing @import at-rules combined with rel=import attributes in LINK elements. The flaw demonstrates characteristics consistent with CWE-416, a use-after-free vulnerability that occurs when memory is freed but subsequently accessed, creating potential exploitation pathways for remote attackers.
The technical exploitation of this vulnerability occurs through carefully crafted JavaScript code that manipulates CSS parsing behavior in a specific manner. When a web page contains a CSS @import at-rule within a token sequence, combined with a LINK element possessing a rel=import attribute, the Blink engine's memory management system encounters a scenario where previously freed memory locations are accessed. This creates a condition where the memory allocator may return freed memory to subsequent allocation requests, potentially allowing attackers to manipulate the program's execution flow or cause arbitrary code execution. The vulnerability operates at the intersection of CSS parsing, JavaScript execution, and memory management within the browser's rendering pipeline, making it particularly dangerous as it can be triggered through web content without requiring user interaction beyond visiting a malicious website.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enabling more severe consequences including remote code execution and privilege escalation. Attackers can leverage this flaw to execute arbitrary code on vulnerable systems, effectively bypassing standard security boundaries. The vulnerability's remote exploitability means that malicious actors can deliver payloads through web browsers without requiring local system access or user interaction beyond visiting compromised websites. This characteristic places it within the ATT&CK framework's technique T1203 for Exploitation for Client Execution, where adversaries use web-based attacks to compromise browser environments. The potential for unspecified other impacts suggests that beyond denial of service, attackers may be able to achieve persistent access, data exfiltration, or system compromise depending on the execution environment.
Mitigation strategies for CVE-2016-5127 require immediate patching of affected Chrome versions to 52.0.2743.82 or later, as this represents the official fix provided by Google. Organizations should implement comprehensive browser update policies and maintain continuous monitoring for similar vulnerabilities in their browser ecosystems. Additional protective measures include implementing Content Security Policy headers to restrict external resource loading, using sandboxing mechanisms, and deploying web application firewalls to detect and block malicious CSS and JavaScript patterns. Security teams should also consider browser hardening configurations that limit CSS parsing capabilities and implement strict resource access controls. The vulnerability highlights the importance of maintaining up-to-date browser security patches and demonstrates how seemingly minor parsing inconsistencies in web standards can create significant security risks. Organizations should also conduct regular security assessments of their browser environments and implement automated patch management systems to ensure timely remediation of such critical vulnerabilities.