CVE-2016-10548 in reduce-css-calc
Summary
by MITRE
Arbitrary code execution is possible in reduce-css-calc node module <=1.2.4 through crafted css. This makes cross sites scripting (XSS) possible on the client and arbitrary code injection possible on the server and user input is passed to the `calc` function.
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Analysis
by VulDB Data Team • 02/10/2020
The vulnerability identified as CVE-2016-10548 represents a critical security flaw within the reduce-css-calc node module version 1.2.4 and earlier. This vulnerability arises from improper handling of user-provided CSS input within the calc function, creating a pathway for arbitrary code execution across both client and server environments. The issue stems from the module's failure to properly sanitize or validate CSS expressions before processing them through the calculation engine, allowing malicious actors to inject crafted CSS that can trigger unintended code execution.
The technical implementation of this vulnerability occurs when the reduce-css-calc module processes CSS content containing malicious calc() expressions. When user input is passed directly to the calc function without adequate sanitization, the module's parser can be manipulated to execute arbitrary JavaScript code. This occurs because the calc function is designed to evaluate mathematical expressions within CSS, but it fails to distinguish between legitimate mathematical operations and malicious code payloads. The vulnerability manifests as a command injection issue where crafted CSS expressions can bypass normal input validation mechanisms and execute code in the context of the application processing the CSS.
The operational impact of this vulnerability extends across multiple attack vectors and environments. On the client side, attackers can leverage this vulnerability to perform cross-site scripting attacks by injecting malicious CSS that executes within user browsers. This creates potential for session hijacking, data theft, and other client-side attacks that compromise user security. On the server side, the vulnerability enables arbitrary code execution, allowing attackers to gain full control over the server environment where the vulnerable module is deployed. This makes the vulnerability particularly dangerous as it can lead to complete system compromise and data breaches.
This vulnerability maps directly to CWE-94, which describes "Improper Control of Generation of Code ('Code Injection')" and aligns with ATT&CK techniques including T1059.007 for Command and Scripting Interpreter and T1203 for Exploitation for Client Execution. The attack surface is particularly concerning because it can be exploited through web applications that process user-uploaded CSS content or dynamic CSS generation without proper input validation. The vulnerability demonstrates poor input sanitization practices and highlights the importance of proper validation in CSS processing libraries. Organizations using affected versions should immediately implement mitigations including updating to patched versions of the reduce-css-calc module, implementing strict input validation for CSS content, and employing web application firewalls to detect and block malicious CSS patterns. The vulnerability also underscores the need for comprehensive security testing of third-party libraries and the importance of maintaining up-to-date dependencies in modern web applications.