CVE-2022-24729: CKEditor4 Denial of Service Vulnerability

CVE-2022-24729 Overview

CVE-2022-24729 is a Regular Expression Denial of Service (ReDoS) vulnerability affecting CKEditor4, a widely-used open source WYSIWYG HTML editor. The vulnerability exists in the dialog plugin where an improperly designed input validator regular expression can be exploited to cause catastrophic backtracking, resulting in significant performance degradation and browser tab freezes.

This vulnerability is particularly concerning for web applications that integrate CKEditor4, as it can be triggered by malicious input through the dialog plugin's validation mechanisms. The attack requires no authentication and can be executed remotely over the network, making it accessible to any user who can interact with an affected CKEditor4 instance.

Critical Impact

Attackers can cause denial of service by triggering exponential regex backtracking, freezing browser tabs and disrupting application availability for end users.

Affected Products

• CKEditor CKEditor versions prior to 4.18.0
• Drupal Drupal (bundled CKEditor4)
• Oracle Application Express
• Oracle Commerce Merchandising 11.3.2
• Oracle Financial Services Analytical Applications Infrastructure
• Oracle Financial Services Behavior Detection Platform
• Oracle Financial Services Trade-based Anti Money Laundering
• Oracle PeopleSoft Enterprise PeopleTools 8.58 and 8.59
• Fedora Project Fedora 36 and 37

Discovery Timeline

• March 16, 2022 - CVE-2022-24729 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-24729

Vulnerability Analysis

This vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption) and CWE-1333 (Inefficient Regular Expression Complexity). The core issue lies within the dialog plugin of CKEditor4, which implements input validation using regular expressions that are susceptible to catastrophic backtracking.

Regular Expression Denial of Service (ReDoS) vulnerabilities occur when a regex pattern contains elements that can match the same input in multiple ways. When crafted input is provided, the regex engine enters a state of exponential time complexity as it attempts to find a match through countless backtracking paths. In CKEditor4's case, the dialog input validator regex exhibits this behavior, allowing an attacker to freeze the browser tab by providing specially crafted input strings.

The attack surface is significant because CKEditor4 is embedded in numerous content management systems, enterprise applications, and web platforms. Any user with access to the editor's dialog functionality could potentially trigger this condition, whether intentionally or accidentally.

Root Cause

The root cause stems from an inefficient regular expression pattern used in the dialog plugin's input validation logic. The regex contains nested quantifiers or alternation patterns that create multiple potential matching paths for the same input characters. When input strings are crafted to exploit these patterns—typically through repetitive character sequences—the regex engine's backtracking mechanism becomes trapped in an exponential number of retry attempts before ultimately failing to match.

This type of vulnerability is a common pitfall in input validation where developers prioritize matching accuracy over computational efficiency. The fix in version 4.18.0 addresses this by redesigning the problematic regular expression to eliminate the conditions that enable catastrophic backtracking.

Attack Vector

The attack vector is network-based and requires no privileges or user interaction beyond access to a page containing the vulnerable CKEditor4 instance. An attacker can craft a malicious input string designed to exploit the regex vulnerability and submit it through any dialog input field that utilizes the flawed validator.

The attack pattern typically involves creating input strings with repetitive character patterns that maximize the number of backtracking iterations. For example, strings containing repeated characters followed by a character that fails the final match condition force the regex engine to explore all possible combinations before concluding there is no match.

The exploitation mechanism works as follows: when the malicious input is processed by the dialog plugin's validator, the regex engine begins matching and quickly encounters scenarios where multiple paths could potentially lead to a match. As it exhausts each path through backtracking, the computational time grows exponentially with input length, eventually consuming enough CPU resources to freeze the browser tab and render the application unresponsive.

For detailed technical information about this vulnerability and the specific regex patterns involved, see the GitHub Security Advisory GHSA-f6rf-9m92-x2hh.

Detection Methods for CVE-2022-24729

Indicators of Compromise

• Unusually high CPU usage in browser processes when users interact with CKEditor4 dialog fields
• Reports of browser tab freezes or unresponsiveness during content editing sessions
• Server-side logs showing repeated or abnormally long requests to endpoints handling CKEditor4 input
• User complaints about editor performance degradation, particularly in dialog-heavy workflows

Detection Strategies

• Implement version scanning of CKEditor4 installations across your environment to identify instances running versions prior to 4.18.0
• Monitor client-side performance metrics for anomalies in JavaScript execution time when CKEditor4 is in use
• Deploy web application firewalls (WAF) with rules to detect and block input patterns commonly associated with ReDoS attacks
• Conduct software composition analysis (SCA) to identify applications bundling vulnerable CKEditor4 versions

Monitoring Recommendations

• Enable detailed logging for applications using CKEditor4 to capture input validation events and processing times
• Set up alerting thresholds for browser performance metrics in environments where CKEditor4 is heavily utilized
• Regularly audit third-party dependencies including CMS platforms like Drupal that bundle CKEditor4
• Monitor vendor security bulletins from Oracle, Drupal, and Fedora for coordinated patch releases

How to Mitigate CVE-2022-24729

Immediate Actions Required

• Upgrade CKEditor4 to version 4.18.0 or later immediately across all affected installations
• For Drupal installations, apply the security update referenced in Drupal Security Advisory SA-CORE-2022-005
• Review Oracle's July 2022 Critical Patch Update for affected Oracle products and apply relevant patches
• Conduct an inventory of all applications using CKEditor4 to ensure comprehensive patching coverage

Patch Information

The vulnerability has been addressed in CKEditor4 version 4.18.0, which was released with the security fix. Organizations should update to this version or later to remediate the vulnerability. The patch modifies the problematic regular expression in the dialog plugin to prevent catastrophic backtracking scenarios.

For CKEditor4 users, the patched version is available through the CKEditor 4.18.0 Release. Drupal users should follow the guidance in the Drupal Security Advisory SA-CORE-2022-005. Oracle customers should consult the Oracle Critical Patch Update July 2022 for patches affecting Oracle products that include CKEditor4.

Fedora users can obtain the updated packages through standard package management channels as referenced in the Fedora Package Announcements.

Workarounds

• According to the security advisory, there are currently no known workarounds for this vulnerability—upgrading to version 4.18.0 is the recommended remediation
• As a temporary measure, consider restricting access to CKEditor4 functionality to trusted users only until patching can be completed
• Implement input length restrictions on dialog fields as a defense-in-depth measure, though this does not fully mitigate the vulnerability
• Monitor for and block suspicious input patterns at the network edge using WAF rules while preparing for the upgrade

# Verify CKEditor4 version in your installation
grep -r "version" /path/to/ckeditor/ckeditor.js | head -5

# For npm-based installations, check the installed version
npm list ckeditor4

# Update CKEditor4 via npm to the patched version
npm update ckeditor4@4.18.0