CVE-2026-115457 in BaserCMS
Summary
by MITRE • 10/23/2026
baserCMS is a website development framework. In versions 5.0.0 before 5.3.2 and 5.4.0 before 5.4.2, global shortcode expansion runs over the complete rendered page, including HTML-escaped blog comments supplied by unauthenticated visitors. A comment containing the BcBaser.getGoogleMaps shortcode can set apiBaseUrl to an attacker-controlled script URL, which is emitted as a script src and executes JavaScript on the site's origin when another visitor or administrator opens the article displaying that comment. Escaping raw HTML in comments does not prevent this stored cross-site scripting because shortcode processing happens after HTML rendering. Other registered shortcodes also expand in comments; Mail.getForm can embed a working contact form with a valid CSRF token. The flaw can compromise the authenticated browser context of an administrator who views the affected article. This issue has been patched in versions 5.3.2 and 5.4.2.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability identified in baserCMS, specifically affecting version ranges prior to 5.3.2 for the 5.x branch and prior to 5.4.2 for the 5.4.x branch, represents a critical failure in input validation and output encoding mechanisms within the application's template rendering engine. This flaw is classified under CWE-79, commonly known as Improper Neutralization of Input During Web Page Generation or Cross-site Scripting (XSS). The core issue stems from the architectural decision to perform global shortcode expansion across the entire rendered page content after HTML escaping has already been applied. In a secure implementation, output encoding should be the final step in the data flow pipeline, ensuring that any dynamic content is treated as inert text unless explicitly and safely processed by trusted components. However, baserCMS processes shortcodes on raw or partially processed strings, allowing malicious payloads embedded within user-supplied data to bypass initial sanitization layers.
The attack vector for this vulnerability relies on stored cross-site scripting (CWE-79: Stored XSS). An unauthenticated attacker can inject a specially crafted comment into the blog section of the website. This comment contains a specific shortcode invocation, such as BcBaser.getGoogleMaps, configured with an apiBaseUrl parameter pointing to a server controlled by the attacker. Because the shortcode processing occurs after HTML escaping, the malicious script tag is not neutralized but rather reconstructed and executed within the context of the victim's browser session. This mechanism effectively bypasses standard Content Security Policy (CSP) protections that might otherwise mitigate simple XSS attacks, as the execution originates from a trusted domain via a legitimate API endpoint configured by the attacker through the shortcode parameter.
The operational impact of this vulnerability is severe due to its ability to compromise authenticated user sessions, particularly those with administrative privileges. When an administrator or any other visitor views an article containing the malicious comment, their browser automatically fetches and executes the JavaScript hosted at the attacker-controlled URL. This script runs in the context of the baserCMS origin, granting it full access to cookies, local storage, and session tokens associated with that domain. For administrators, this can lead to complete account takeover, allowing the attacker to modify site configurations, inject further malware, or exfiltrate sensitive data stored within the CMS database. The vulnerability is not limited to script execution; other registered shortcodes like Mail.getForm can be exploited to embed functional contact forms that include valid CSRF tokens. This allows attackers to perform actions on behalf of authenticated users without their knowledge, facilitating unauthorized form submissions and further compromising system integrity.
This flaw aligns with the MITRE ATT&CK technique T1059.007, JavaScript Web Browser Execution, as it involves the execution of malicious scripts within a victim's browser environment through legitimate application features. It also relates to CWE-642, External Control of Critical State Data, because the attacker controls parameters that dictate how internal components behave. The persistence of the payload in stored comments makes this a high-severity issue compared to reflected XSS variants, as it requires no social engineering beyond convincing users or admins to view specific content.
Mitigation for this vulnerability is primarily achieved by upgrading baserCMS to version 5.3.2 or later, where the rendering pipeline has been corrected to ensure that shortcodes are processed in a context-aware manner that respects output encoding boundaries. Until an upgrade can be performed, administrators should implement strict input validation on all comment fields and disable unnecessary shortcode expansions for untrusted content types. Additionally, deploying a robust Web Application Firewall (WAF) with rules specifically targeting malicious script injections and anomalous API parameter usage can provide a layer of defense against exploitation attempts. Regular security audits focusing on the order of operations in template rendering engines are recommended to prevent similar architectural flaws in future development cycles.