CVE-2021-32764 in Discourse
Summary
by MITRE • 07/16/2021
Discourse is an open-source discussion platform. In Discourse versions 2.7.5 and prior, parsing and rendering of YouTube Oneboxes can be susceptible to XSS attacks. This vulnerability only affects sites which have modified or disabled Discourse's default Content Security Policy. The issue is patched in `stable` version 2.7.6, `beta` version 2.8.0.beta3, and `tests-passed` version 2.8.0.beta3. As a workaround, ensure that the Content Security Policy is enabled, and has not been modified in a way which would make it more vulnerable to XSS attacks.
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Analysis
by VulDB Data Team • 07/19/2021
The vulnerability CVE-2021-32764 affects Discourse, an open-source discussion platform that serves as a collaborative forum solution for communities and organizations. This security flaw specifically targets the YouTube Onebox functionality, which allows users to embed YouTube videos directly into discussion threads. The vulnerability manifests when the platform processes and renders YouTube content through its Onebox feature, creating a potential attack vector for cross-site scripting exploits. The issue represents a significant security concern as it could enable malicious actors to inject arbitrary JavaScript code into user sessions, potentially compromising user data and system integrity.
The technical flaw stems from insufficient input validation and sanitization within Discourse's YouTube Onebox parsing mechanism. When users embed YouTube links within discussion posts, the platform processes these URLs and generates HTML content for display. In versions 2.7.5 and earlier, the parsing logic fails to adequately sanitize user-provided YouTube content, particularly when combined with specific configuration modifications. This vulnerability requires a specific prerequisite: sites must have modified or disabled the default Content Security Policy (CSP) configuration. The absence of proper CSP enforcement creates an exploitable condition where malicious JavaScript code can be injected and executed within the context of legitimate user sessions. This vulnerability maps to CWE-79, Cross-site Scripting, and specifically aligns with ATT&CK technique T1566.001, "Phishing via Social Media", as attackers could craft malicious YouTube content to exploit this vulnerability.
The operational impact of CVE-2021-32764 extends beyond simple data theft or session hijacking. Organizations using Discourse as their primary communication platform face potential compromise of user credentials, private messages, and sensitive discussion content. Attackers could leverage this vulnerability to execute malicious scripts that monitor user interactions, steal authentication tokens, or redirect users to phishing sites. The vulnerability's exploitation requires specific conditions, as it only affects installations with modified CSP policies, but this limitation does not diminish its severity. The risk is particularly elevated for organizations that have customized their security configurations without proper understanding of the implications. Security teams must consider the potential for lateral movement within networks if compromised user sessions contain administrative privileges or access to sensitive systems.
Mitigation strategies for CVE-2021-32764 focus on both immediate remediation and long-term security hardening. The primary solution involves upgrading to patched versions of Discourse, specifically stable version 2.7.6, beta version 2.8.0.beta3, or tests-passed version 2.8.0.beta3, which contain the necessary code modifications to properly sanitize YouTube Onebox content. Organizations should immediately implement the recommended workaround of ensuring that the Content Security Policy is enabled and properly configured, avoiding any modifications that would weaken the security posture. Security teams should conduct thorough audits of their Discourse configurations to identify any CSP modifications that might create vulnerabilities. Additionally, implementing proper input validation, output encoding, and regular security assessments can help prevent similar issues in the future. Organizations should also consider implementing web application firewalls and monitoring for suspicious embedding patterns within discussion forums. The vulnerability highlights the importance of maintaining default security configurations and avoiding unnecessary customizations that could create security gaps, particularly in widely used open-source platforms like Discourse that serve as communication hubs for sensitive information exchanges.