CVE-2026-95529 in Calculated Fields Form Plugin
Summary
by MITRE • 09/23/2026
Unauthenticated Cross Site Scripting (XSS) in Calculated Fields Form <= 5.5.1.1 versions.
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Analysis
by VulDB Data Team • 09/23/2026
The vulnerability identified as an unauthenticated cross-site scripting flaw within the Calculated Fields Form plugin for WordPress, affecting versions up to and including 5.5.1.1, represents a significant security risk due to its lack of authentication requirements. This specific characteristic allows any user with access to the public-facing website to exploit the weakness without needing valid credentials or prior login sessions. The core technical flaw stems from insufficient input validation and sanitization mechanisms within the plugin's handling of form data submitted by users. When malicious scripts are injected into these fields, they are processed and rendered directly in the browser context of other visitors who view the resulting content or interact with the affected forms. This failure to properly encode special characters such as angle brackets, quotes, and ampersands enables the execution of arbitrary JavaScript code within the victim's session environment.
From a technical perspective, this vulnerability aligns closely with CWE-79, which describes Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The attack vector typically involves an attacker crafting a malicious payload that is embedded in a form field designed to calculate values or process user input. Because the plugin does not adequately filter out script tags or event handlers before storing or displaying this data, the browser interprets these inputs as executable code rather than plain text. This behavior violates fundamental web security principles regarding output encoding and context-aware sanitization. The absence of authentication requirements exacerbates the severity because it removes a critical layer of defense that would otherwise restrict access to administrative functions or sensitive user interactions, thereby broadening the attack surface to include all anonymous visitors.
The operational impact of this vulnerability is substantial, primarily centering on session hijacking and credential theft through cookie manipulation. An attacker can exploit the unauthenticated nature of the XSS flaw to steal administrator cookies by injecting a script that exfiltrates these tokens to an external server controlled by the adversary. Once obtained, these cookies allow the attacker to impersonate legitimate administrators, gaining full control over the WordPress installation. This level of access enables further malicious activities such as defacing the website, installing backdoors, or accessing sensitive database information containing user data and business logic. Additionally, the vulnerability can be used for phishing attacks where users are redirected to fraudulent login pages designed to capture their credentials, leveraging the trust associated with the legitimate domain hosting the vulnerable plugin.
In terms of industry frameworks, this incident maps directly to MITRE ATT&CK technique T1059.007, which covers JavaScript execution within web browsers as part of client-side code injection attacks. The unauthenticated aspect places it in a high-risk category for public-facing applications where defense-in-depth strategies are often bypassed by external actors. Mitigation efforts must prioritize immediate updates to the latest patched version of Calculated Fields Form if available from official repositories, ensuring that developers have addressed the input validation gaps. For organizations unable to update immediately due to compatibility concerns with other plugins or custom code implementations, implementing a Web Application Firewall is recommended as an interim control measure. Such firewalls can detect and block common XSS payloads by analyzing request patterns for suspicious script injections before they reach the application logic.
Further mitigation strategies include enforcing strict Content Security Policy headers that restrict the execution of inline scripts and limit sources from which external resources can be loaded. This approach reduces the effectiveness of injected payloads even if validation fails, as the browser will refuse to execute unauthorized code blocks. Additionally, developers should review custom form handling routines to ensure consistent application of output encoding functions such as htmlspecialchars or equivalent context-specific sanitizers across all user inputs. Regular security audits and penetration testing focused on input validation weaknesses are essential for maintaining long-term resilience against similar injection-based threats in dynamic web applications built with WordPress ecosystems.