CVE-2006-1336 in ExtCalendar
Summary
by MITRE
Cross-site scripting vulnerability in calendar.php in ExtCalendar 1.0 and possibly other versions before 2.0 allows remote attackers to inject arbitrary web script or HTML via the (1) year, (2) month, (3) next, and (4) prev parameters.
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Analysis
by VulDB Data Team • 10/18/2025
The vulnerability identified as CVE-2006-1336 represents a classic cross-site scripting flaw within the ExtCalendar 1.0 web application, specifically affecting the calendar.php script. This issue demonstrates a critical weakness in input validation and output sanitization mechanisms that allows malicious actors to inject arbitrary web scripts or HTML content into the application's response. The vulnerability affects not only version 1.0 but potentially all versions prior to the 2.0 release, indicating a widespread flaw that has persisted across multiple iterations of the software. The attack vector targets four specific parameters within the calendar.php script: year, month, next, and prev, which are commonly used for navigation and display purposes in calendar applications. These parameters are typically used to control the calendar view, with year and month determining the displayed time period, while next and prev handle navigation between different time frames. The flaw occurs when these parameters are directly incorporated into the web page output without proper sanitization or encoding, creating an environment where attacker-controlled input can be executed as client-side script in the context of other users' browsers.
The technical exploitation of this vulnerability follows the standard XSS attack pattern where malicious input is accepted through web forms or URL parameters and then rendered back to users without proper validation or encoding. In this case, the year, month, next, and prev parameters serve as entry points for attackers to inject script tags, JavaScript code, or HTML elements that will execute in the browsers of unsuspecting users who view the affected calendar pages. The impact extends beyond simple script execution as it can enable session hijacking, credential theft, defacement of calendar content, or redirection to malicious websites. According to CWE classification, this vulnerability maps to CWE-79 which specifically addresses Cross-site Scripting flaws, and more specifically to CWE-74 which deals with Improper Neutralization of Special Elements in Output Used by a Downstream Component. The vulnerability's persistence across versions suggests that fundamental architectural issues in input handling were not properly addressed during the software development lifecycle.
The operational impact of CVE-2006-1336 is significant for organizations using ExtCalendar 1.0 or earlier versions, as it creates a persistent security risk that can be exploited by remote attackers without requiring authentication or privileged access. Users who view calendar pages containing malicious input could have their browser sessions compromised, potentially leading to unauthorized access to sensitive information or system resources. The vulnerability's nature makes it particularly dangerous because it can be exploited through simple URL manipulation, making it easily accessible to attackers with minimal technical expertise. From an ATT&CK framework perspective, this vulnerability aligns with techniques such as T1566 (Phishing) and T1059 (Command and Scripting Interpreter) as attackers can use the XSS vector to deliver malicious payloads that can escalate privileges or perform unauthorized actions on behalf of users. The long lifespan of this vulnerability across multiple versions also indicates poor security practices in the software development process, suggesting that security testing and code review were not adequately implemented during the development lifecycle.
Organizations affected by this vulnerability should immediately implement mitigations including input validation and output encoding for all parameters used in calendar.php and similar scripts. The most effective immediate solution involves implementing proper HTML entity encoding for all user-supplied input before rendering it in web pages, which prevents script execution regardless of the content. Additionally, implementing Content Security Policy headers can provide an additional layer of protection by restricting the sources from which scripts can be loaded. Long-term remediation requires upgrading to ExtCalendar 2.0 or later versions where the vulnerability has been addressed, along with establishing comprehensive input validation procedures and regular security testing protocols. Security teams should also consider implementing web application firewalls to detect and block suspicious parameter values, while conducting regular vulnerability assessments to identify similar flaws in other applications. The vulnerability serves as a reminder of the importance of secure coding practices and the need for continuous security monitoring to prevent exploitation of known weaknesses in widely used web applications.