CVE-2022-31059 is a cross-site scripting (XSS) vulnerability identified in the discourse-calendar plugin, a calendar extension for Discourse, an open-source messaging platform. The vulnerability arises from improper neutralization of input during web page generation (CWE-79), specifically in the parsing and rendering of event names within the plugin. Versions of discourse-calendar prior to 1.0.1 are affected. The vulnerability is exploitable only on Discourse sites that have either modified or disabled the default Content Security Policy (CSP) settings, which normally provide a robust defense against XSS attacks. In such configurations, malicious actors can inject crafted scripts into event names that, when rendered, execute in the context of the victim's browser. This can lead to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The issue was addressed and patched in discourse-calendar version 1.0.1 by properly sanitizing input and enforcing secure rendering practices. No known exploits have been reported in the wild to date. The vulnerability requires no authentication or user interaction beyond viewing the maliciously crafted event name, assuming the CSP is weakened or disabled. The risk is medium severity due to the dependency on CSP misconfiguration and the limited scope of the plugin's deployment. However, the impact on confidentiality and integrity can be significant if exploited, especially in environments where sensitive communications occur via Discourse platforms.

For European organizations using Discourse with the discourse-calendar plugin, this vulnerability poses a risk primarily to the confidentiality and integrity of user sessions and data. Successful exploitation could allow attackers to execute arbitrary scripts in the context of authenticated users, potentially leading to theft of session cookies, unauthorized access, or manipulation of user data. Organizations relying on Discourse for internal communications, project management, or community engagement may face reputational damage, data breaches, or compliance issues under GDPR if user data is compromised. The impact is heightened in sectors with stringent data protection requirements such as finance, healthcare, and government. However, the vulnerability's reliance on CSP misconfiguration limits its exploitability, meaning well-configured environments are less at risk. Nonetheless, organizations that have customized or weakened CSP policies to enable additional functionality or third-party integrations should consider this vulnerability a significant threat vector.

1. Upgrade the discourse-calendar plugin to version 1.0.1 or later immediately to apply the official patch that addresses the XSS vulnerability. 2. Review and enforce strict Content Security Policy configurations on all Discourse instances, ensuring that CSP is enabled and not weakened or disabled. Avoid overly permissive directives such as 'unsafe-inline' or 'unsafe-eval' that can facilitate script injection. 3. Conduct a thorough audit of all customizations and third-party plugins that may alter CSP or input sanitization mechanisms within Discourse. 4. Implement input validation and output encoding best practices for any custom event name inputs or other user-generated content fields. 5. Monitor Discourse logs and user reports for suspicious activity or unexpected script execution behaviors. 6. Educate administrators and developers on the importance of CSP and secure coding practices to prevent similar vulnerabilities. 7. If upgrading immediately is not feasible, temporarily restrict event name inputs to a safe subset of characters or disable the discourse-calendar plugin until patched.