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How the Vulnerability (CVE-2026-48527) Works
HAX CMS is a platform for managing microsites with either PHP or Node.js backends. Versions up to and including 26.0.0 contain a stored cross-site scripting (XSS) vulnerability within the `/system/api/saveNode` endpoint. This flaw allows an authenticated user with page editing permissions to bypass the built-in HTML sanitizer and inject malicious JavaScript code.
The root cause of this vulnerability lies in a flawed, regex-based HTML sanitization mechanism. The sanitizer is designed to remove potentially dangerous attributes from HTML tags, such as event handlers like `onclick` or onload. To do this, it specifically looks for a pattern where a whitespace character (e.g., space) separates the tag attribute from an event handler, like href="" onclick="...".
However, the sanitizer’s logic fails when a different, yet entirely valid, HTML syntax is used. Specifically, if an event handler attribute is placed immediately after the preceding attribute or HTML tag without any whitespace in between, like href=""onclick="...", the regex pattern used by the sanitizer does not recognize it as a threat. Consequently, the entire malicious payload remains untouched within the `node.body` value, which is then stored in the generated page files, such as index.html.
When a user later clicks the infected link (<a href=""onclick="alert('kn1ph')">click me</a>), the web browser correctly interprets `onclick` as a valid JavaScript event handler. This results in the execution of the attacker’s script within the context of the victim’s browser. An attacker could use this to steal sensitive data, like JWT tokens stored in `localStorage.jwt` or API paths and tokens from window.appSettings, potentially leading to a full account takeover.
DailyCVE Form:
Platform: HaxCMS (Node.js/PHP)
Version: ≤ 26.0.0
Vulnerability: Stored XSS Bypass
Severity: High
date: 2026-05-29
Prediction: 2026-06-15
What Undercode Say:
From the analysis of CVE-2026-48527, the following actions can be taken to detect and verify the vulnerability.
Search for any instances of event handlers without whitespace in generated site files
grep -rnw '/var/www/html/haxcms/sites//' -e 'href=""onclick=' -e 'href=""onload='
Alternatively, use a more comprehensive regex to catch various patterns
find /var/www/html/haxcms/sites/ -name ".html" -exec grep -P 'href="[^"]"\K(on\w+)=(".?")' {} \;
Example cURL command to exploit the vulnerability by changing the page body
curl -X POST "https://target.haxcms.com/system/api/saveNode?site_token=YOUR_VALID_TOKEN" \
-H "Content-Type: application/json" \
-d '{"node": {"body": "Existing page content...\n<a href=\"\"onclick=\"alert(\\\"CVE-2026-48527\\\")\">Click for XSS</a>"}}'
How Exploit:
An authenticated attacker would follow these steps to exploit this vulnerability:
1. Log in to the HaxCMS instance.
- Navigate to any page they have permission to edit.
- Intercept the page save request using a web proxy like Burp Suite. The request is made to
POST /system/api/saveNode?site_token=[bash]. - In the JSON body, modify the `node.body` parameter, changing its content from benign text to include a malicious link, such as
"body":"...existing page content...\n<a href=\"\"onclick=\"alert('kn1ph')\">click me</a>\n".
5. Forward the modified request to the server.
- When any user visits the edited page and clicks the newly created “click me” link, the JavaScript payload will execute, potentially stealing session tokens or performing actions on behalf of the victim.
Protection:
- Update the software: The most effective protection is to update to @haxtheweb/haxcms-nodejs version 26.0.1 or haxcms-php version 26.0.2 or later, where the sanitizer has been fixed.
- Implement a Web Application Firewall (WAF): A WAF rule can be configured to block requests containing HTML event handler attributes without leading whitespace.
- Enforce Content Security Policy (CSP): A strict CSP can mitigate the impact of XSS by preventing the execution of inline scripts or restricting the domains from which scripts can be loaded.
Impact:
- Stored Cross-Site Scripting (XSS): An attacker can inject persistent malicious scripts that are stored on the server and executed in the browsers of any user who visits the compromised page.
- Data Theft: The injected script can access any data the victim’s browser can access on the HaxCMS site. This includes session tokens (JWT), API keys, and other sensitive information stored in `localStorage` or
window.appSettings. - Account Takeover: By stealing a privileged user’s session token, an attacker can impersonate them and gain administrative control over the CMS.
- Privilege Escalation: A low-privileged authenticated user can escalate their privileges by compromising a higher-privileged user who clicks the malicious link.
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Sources:
Reported By: nvd.nist.gov
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