CVE-2023-48631: Adobe Css-tools DOS Vulnerability

CVE-2023-48631 Overview

CVE-2023-48631 is an Improper Input Validation vulnerability affecting @adobe/css-tools versions 4.3.1 and earlier. This Node.js package, commonly used for CSS parsing and manipulation in web development workflows, is susceptible to a denial of service condition when processing specially crafted CSS input. The vulnerability stems from insufficient validation of CSS content during parsing operations, allowing attackers to exhaust system resources through malicious input.

Critical Impact

Attackers can trigger a denial of service condition by supplying malformed CSS input, potentially disrupting build pipelines, CI/CD systems, and web applications that rely on this package for CSS processing.

Affected Products

• Adobe css-tools versions 4.3.1 and earlier
• Node.js applications utilizing @adobe/css-tools for CSS parsing
• Build systems and development toolchains incorporating the vulnerable package

Discovery Timeline

• 2023-12-14 - CVE-2023-48631 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-48631

Vulnerability Analysis

This vulnerability is classified under CWE-20 (Improper Input Validation) and CWE-1333 (Inefficient Regular Expression Complexity). The core issue lies in how the @adobe/css-tools library handles CSS input during parsing operations. When processing CSS content, the parser fails to adequately validate or sanitize input, creating an opportunity for resource exhaustion attacks.

The CWE-1333 classification indicates that regular expression patterns used within the CSS parsing logic may be susceptible to catastrophic backtracking—a condition where specially crafted input causes exponential time complexity in regex evaluation. This type of vulnerability, often referred to as ReDoS (Regular Expression Denial of Service), can cause the application to hang or consume excessive CPU resources when processing malicious input.

Root Cause

The root cause is the combination of improper input validation and inefficient regular expression complexity in the CSS parsing implementation. The library does not implement adequate safeguards against pathological input patterns that can trigger worst-case performance scenarios in the regex engine. Without proper input length limits, complexity bounds, or regex optimization, attackers can craft CSS strings that cause the parser to enter computationally expensive processing loops.

Attack Vector

The vulnerability is exploitable over the network without authentication or user interaction. An attacker can deliver malicious CSS content through various vectors depending on how the target application uses the library:

• Submitting crafted CSS through form inputs or API endpoints that process user-provided stylesheets
• Injecting malicious CSS through content management systems or theme editors
• Compromising upstream dependencies or CDN resources to serve malicious CSS
• Targeting build systems by introducing malicious CSS files into source repositories

When the vulnerable @adobe/css-tools library attempts to parse the malicious CSS, it enters a denial of service state, potentially blocking the Node.js event loop and rendering the application unresponsive.

The attack exploits weaknesses in the CSS parsing regular expressions. When specially crafted CSS input is provided, the regex engine may experience catastrophic backtracking, consuming excessive CPU cycles. For detailed technical analysis, refer to the GitHub Security Advisory.

Detection Methods for CVE-2023-48631

Indicators of Compromise

• Sudden CPU spikes or sustained high CPU utilization on servers running Node.js applications with @adobe/css-tools
• Application hangs or unresponsiveness during CSS processing operations
• Timeout errors in build pipelines or CI/CD systems involving CSS compilation
• Increased response latency or service degradation correlated with CSS input processing

Detection Strategies

• Implement software composition analysis (SCA) to identify instances of @adobe/css-tools versions 4.3.1 and earlier in your codebase
• Monitor application performance metrics for anomalous CPU usage patterns during CSS parsing operations
• Deploy web application firewalls (WAF) with rules to detect and block abnormally large or malformed CSS payloads
• Use npm audit or similar dependency scanning tools to flag vulnerable package versions

Monitoring Recommendations

• Enable detailed logging for CSS processing operations to capture input patterns associated with performance degradation
• Configure alerting thresholds for CPU utilization and event loop lag in Node.js applications
• Implement request timeout mechanisms to limit the impact of long-running CSS parsing operations
• Monitor dependency vulnerability databases and security advisories for updates related to this CVE

How to Mitigate CVE-2023-48631

Immediate Actions Required

• Audit all projects and applications to identify usage of @adobe/css-tools versions 4.3.1 and earlier
• Update @adobe/css-tools to version 4.3.2 or later, which contains the security fix
• Review and update lock files (package-lock.json, yarn.lock) to ensure transitive dependencies also use the patched version
• Implement input size limits for CSS content accepted by your applications as a defense-in-depth measure

Patch Information

Adobe has addressed this vulnerability in @adobe/css-tools version 4.3.2. Organizations should update to this version or later to remediate the vulnerability. The fix addresses the improper input validation and regex complexity issues that enable the denial of service condition.

For complete details on the fix and affected versions, see the GitHub Security Advisory.

Workarounds

• Implement input validation and size limits on CSS content before passing it to the parsing library
• Deploy rate limiting on endpoints that accept CSS input to reduce the impact of potential attacks
• Consider isolating CSS parsing operations in separate processes or worker threads to prevent main application blocking
• Use timeouts around CSS parsing operations to prevent indefinite hangs

# Update @adobe/css-tools to patched version
npm update @adobe/css-tools

# Or install specific patched version
npm install @adobe/css-tools@4.3.2

# Verify installed version
npm list @adobe/css-tools

# Run dependency audit to check for vulnerabilities
npm audit