CVE-2026-81300 in Calculation for Contact Form 7 Plugin
Summary
by MITRE • 09/03/2026
Unauthenticated Cross Site Scripting (XSS) in Calculation For Contact Form 7 <= 1.0 versions.
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Analysis
by VulDB Data Team • 09/03/2026
The vulnerability identified as an unauthenticated cross-site scripting flaw within the Calculation for Contact Form 7 plugin, specifically affecting versions up to and including 1.0, represents a significant security risk for websites utilizing this WordPress extension. This plugin is designed to enhance standard contact forms by allowing users to perform mathematical calculations based on form inputs, such as calculating total costs or quantities dynamically before submission. The core issue lies in the insufficient sanitization of user-supplied input data that feeds into these calculation functions. Because the vulnerability is unauthenticated, it does not require any prior login credentials or privilege escalation, making it accessible to any internet user who can interact with a vulnerable form on the target website. This characteristic significantly lowers the barrier for exploitation, allowing attackers from anywhere on the web to initiate an attack without needing to bypass authentication mechanisms first.
From a technical perspective, the flaw stems directly from improper input validation and output encoding practices within the plugin's codebase. When a user submits data through a contact form enhanced by this plugin, the system processes these inputs to execute mathematical operations. However, the implementation fails to adequately sanitize special characters or encode HTML entities before rendering the results back into the browser context. Consequently, an attacker can inject malicious JavaScript payloads directly into the input fields of the form. When the page loads and attempts to display the calculated result or process the submission, the embedded script executes in the victim's web browser with the same privileges as legitimate scripts loaded from the site. This execution occurs within the security context of the vulnerable website, granting the attacker a level of trust that can be exploited for various malicious purposes.
The operational impact of this vulnerability is severe and multifaceted, primarily centering on session hijacking and data theft. By executing arbitrary JavaScript in the victim's browser, an attacker can steal sensitive information such as authentication cookies, session tokens, or personally identifiable information entered into other forms on the same domain. This capability allows for account takeover attacks if the stolen credentials are used to access administrative panels or user accounts. Furthermore, the vulnerability enables phishing attacks where the attacker can manipulate the page content to display fake login prompts or malicious links that trick users into revealing their own credentials. In more advanced scenarios, the injected script could be used to perform actions on behalf of the victim without their knowledge, such as changing account settings, making purchases, or spreading malware by redirecting traffic to malicious sites. This undermines the integrity and confidentiality of both user data and website operations.
This vulnerability aligns with CWE-79, which classifies Improper Neutralization of Input During Web Page Generation commonly known as Cross-site Scripting. The specific vector here involves reflected or stored XSS depending on how the plugin handles form submissions and displays results, but in either case, it falls under the broader category of input validation failures. In terms of threat modeling and attack patterns, this exploit maps to MITRE ATT&CK technique T1059, specifically Command Line Interface scripting via JavaScript execution within a browser environment. It also relates to T1204, User Execution, where the victim is tricked into performing an action that leads to code execution. Understanding these mappings helps security professionals categorize the risk accurately and prioritize remediation efforts based on established industry standards for web application security.
Mitigation strategies must focus on immediate patching and robust input handling practices. The primary recommendation is to upgrade the Calculation for Contact Form 7 plugin to a version newer than 1.0, where developers have presumably addressed these sanitization issues by implementing proper output encoding functions such as htmlspecialchars or wp_kses in PHP before rendering data into HTML contexts. For organizations unable to update immediately due to compatibility constraints, temporary mitigations include deploying Web Application Firewalls configured with rules that detect and block common XSS payloads within form submission parameters. Additionally, enforcing strict Content Security Policy headers can help mitigate the impact by restricting the sources from which scripts are allowed to execute, thereby preventing the injected malicious code from running even if it is successfully inserted into the page source. Regular security audits and penetration testing of custom plugins should be conducted to ensure that similar input validation flaws do not exist elsewhere in the application stack.