CVE-2026-119714 in My Calendar Plugin
Summary
by MITRE • 10/30/2026
My Calendar WordPress plugin 3.8.8 before 3.8.11 contains a shortcode injection vulnerability that allows unauthenticated attackers to execute registered shortcodes via the mcs search parameter. The mcs value reaches mc_search_results() in src/my-calendar-search.php without bracket encoding before do_shortcode runs, so a GET request triggers shortcodes on any page or post, enabling content injection and spoofing.
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Analysis
by VulDB Data Team • 10/30/2026
The vulnerability identified in My Calendar WordPress plugin versions prior to 3.8.11 represents a critical shortcode injection flaw that stems from insufficient input sanitization within the search functionality. Specifically, the mcs parameter is processed by the mc_search_results function located in src/my-calendar-search.php without proper encoding of bracket characters before being passed to the do_shortcode routine. This architectural oversight allows unauthenticated attackers to inject arbitrary shortcodes into the application context via a simple GET request. Because WordPress executes these shortcodes upon rendering, an attacker can manipulate the output displayed on any page or post where this search functionality is active, effectively bypassing standard authentication mechanisms required for most administrative actions within the platform.
From a technical perspective, the core issue lies in the failure to escape square brackets before invoking the shortcode parser. In WordPress development best practices, user-supplied input that may contain special characters must be sanitized or escaped appropriately depending on its intended use case. When shortcodes are involved, inputs containing opening and closing brackets can trigger execution of registered plugins' functions if not properly handled. By injecting crafted payloads into the mcs parameter, an attacker forces the system to interpret malicious content as legitimate shortcode syntax. This leads to unintended code execution within the context of the current user session or even globally depending on how the targeted shortcodes are implemented by other installed plugins or themes.
The operational impact of this vulnerability is significant due to its potential for cross-site scripting, data exfiltration, and site defacement. Attackers can exploit this flaw to inject malicious scripts that steal cookies, capture sensitive information such as login credentials through phishing pages hosted via injected content, or alter the visual presentation of the website to deceive visitors. Furthermore, if specific shortcodes allow administrative actions when triggered by certain parameters, an attacker might escalate privileges without needing valid authentication. This type of attack falls under CWE-79 Improper Neutralization of Input During Web Page Generation commonly known as Cross-Site Scripting but specifically manifests here through shortcode injection rather than direct script tag insertion.
In terms of threat modeling and industry standards, this vulnerability aligns with MITRE ATT&CK technique T1059 Command and Control via Application Layer Protocol since it involves manipulating application logic to execute arbitrary commands or scripts. It also relates to CWE-20 Improper Input Validation as the root cause is the lack of rigorous validation on user-supplied data entering critical processing functions. The ability for unauthenticated actors to trigger these effects highlights a severe gap in access control and input handling procedures within the plugin's codebase, making it particularly dangerous against sites with high traffic or sensitive content where trust from visitors is paramount.
Mitigation strategies should prioritize immediate updating of the My Calendar WordPress plugin to version 3.8.11 or later which addresses this specific flaw by implementing proper escaping mechanisms for bracket characters before shortcode processing occurs. Administrators unable to update immediately should consider disabling search functionality if not essential, restricting access to pages containing vulnerable shortcodes through IP whitelisting or authentication requirements where feasible, and deploying Web Application Firewalls configured to detect and block patterns indicative of shortcode injection attempts. Regular security audits focusing on input validation practices across all active plugins will help prevent similar vulnerabilities from being introduced in the future ensuring long-term resilience against such exploitation vectors.