CVE-2022-25758: Scss-tokenizer ReDoS Vulnerability

CVE-2022-25758 Overview

All versions of the scss-tokenizer package are vulnerable to Regular Expression Denial of Service (ReDoS) via the loadAnnotation() function. This vulnerability arises from the usage of an insecure regular expression pattern that can be exploited by attackers to cause significant CPU consumption, leading to denial of service conditions in applications that process untrusted SCSS input.

Critical Impact

Network-accessible applications using scss-tokenizer can be rendered unresponsive through crafted SCSS input that triggers catastrophic backtracking in the vulnerable regex pattern, causing high availability impact.

Affected Products

• scss-tokenizer (all versions) for Node.js
• WebJars npm packages containing scss-tokenizer
• Applications and build pipelines using scss-tokenizer for SCSS parsing

Discovery Timeline

• 2022-07-01 - CVE-2022-25758 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2022-25758

Vulnerability Analysis

This vulnerability is classified as CWE-1333 (Inefficient Regular Expression Complexity). The loadAnnotation() function in scss-tokenizer contains a regular expression that exhibits catastrophic backtracking behavior when processing specially crafted input strings. Regular Expression Denial of Service (ReDoS) attacks exploit the exponential time complexity that can occur in regex engines when certain patterns are matched against malicious input.

In the context of scss-tokenizer, this vulnerability is particularly concerning because the package is commonly used in build pipelines and development toolchains to process SCSS/Sass stylesheets. An attacker who can influence the SCSS content being processed—whether through user-uploaded stylesheets, untrusted third-party dependencies, or other input vectors—can craft input that causes the regex engine to consume excessive CPU resources.

Root Cause

The root cause of this vulnerability lies in the inefficient regular expression pattern used within the loadAnnotation() function. The regex contains constructs that allow for exponential time complexity during the matching process. When the regex engine encounters input designed to maximize backtracking, it can result in the application becoming unresponsive for extended periods.

Insecure regex patterns often contain nested quantifiers, overlapping character classes, or ambiguous matching sequences that force the regex engine to explore an exponentially growing number of possible matches before determining success or failure.

Attack Vector

The attack can be executed remotely over the network without requiring authentication or user interaction. An attacker needs to supply malicious SCSS content to an application that uses scss-tokenizer for parsing. The attack vector requires identifying applications that:

1. Accept SCSS input from untrusted sources
2. Use the vulnerable scss-tokenizer package to process this input
3. Do not implement timeouts or resource limits on regex processing

When the malicious input is processed by the loadAnnotation() function, the vulnerable regex pattern enters a state of catastrophic backtracking, consuming CPU cycles proportional to the exponential complexity of the input, effectively causing a denial of service condition.

For detailed technical information about this vulnerability, refer to the GitHub Issue #45 which documents the vulnerable pattern.

Detection Methods for CVE-2022-25758

Indicators of Compromise

• Abnormally high CPU utilization in Node.js processes running scss-tokenizer
• Application hangs or timeouts during SCSS compilation or parsing operations
• Build pipeline failures or excessive build times when processing SCSS files
• Memory consumption spikes in applications processing stylesheets

Detection Strategies

• Implement Software Composition Analysis (SCA) tools to identify scss-tokenizer in your dependency tree
• Use npm audit or yarn audit to detect known vulnerabilities in installed packages
• Monitor for packages containing scss-tokenizer through the Snyk JavaScript vulnerability database
• Review application logs for timeout errors related to SCSS processing

Monitoring Recommendations

• Configure alerting on CPU utilization thresholds for Node.js application processes
• Implement request timeout monitoring for endpoints that process user-supplied SCSS
• Set up build pipeline duration monitoring to detect abnormal processing times
• Monitor for repeated regex execution timeouts in application logs

How to Mitigate CVE-2022-25758

Immediate Actions Required

• Audit your application dependencies for scss-tokenizer using npm ls scss-tokenizer or equivalent
• Implement input validation and size limits on any user-supplied SCSS content
• Add timeout mechanisms around SCSS processing operations to limit execution time
• Consider switching to alternative SCSS tokenization libraries that are not affected

Patch Information

As of the last update, all versions of scss-tokenizer are reported as vulnerable. Check the scss-tokenizer GitHub repository for the latest information on fixes or patches. Organizations should evaluate whether the package maintainers have released a patched version or consider migrating to an alternative library.

For Java WebJars environments, consult the Snyk Java vulnerability advisory for guidance specific to that ecosystem.

Workarounds

• Implement execution timeouts for SCSS parsing operations to prevent indefinite CPU consumption
• Restrict SCSS input sources to trusted origins only and validate input before processing
• Sandbox SCSS processing in isolated worker threads with resource limits
• Use web application firewalls (WAF) to filter potentially malicious SCSS patterns

# Configuration example - Check for vulnerable package in your project
npm ls scss-tokenizer
# Review if scss-tokenizer is a direct or transitive dependency

# Set Node.js resource limits when running SCSS processing
NODE_OPTIONS="--max-old-space-size=512" npm run build

# Use timeout wrapper for SCSS processing scripts
timeout 30s npm run scss-compile