CVE-2026-53963 in Discourse
Summary
by MITRE • 07/10/2026
Discourse is an open-source discussion platform. Prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, a malicious second factor name on an attacker-controlled account was not escaped in the delete confirmation dialog, allowing stored cross-site scripting when an administrator impersonated that account. This issue is fixed in versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5.
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Analysis
by VulDB Data Team • 07/10/2026
This vulnerability affects Discourse, an open-source discussion platform that facilitates community engagement through threaded conversations and user interactions. The security flaw manifests in the platform's handling of second factor authentication names within administrative delete confirmation dialogs. Prior to specific version releases including 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, the application failed to properly escape user-controlled input when displaying second factor names in administrative interfaces. This oversight creates a persistent cross-site scripting vulnerability that can be exploited by malicious actors seeking to compromise administrator accounts.
The technical flaw resides in the insufficient output encoding or escaping of user-supplied data within the delete confirmation dialog mechanism. When an administrator attempts to delete an account, the system displays a confirmation dialog that includes the second factor name associated with the target account. If an attacker controls an account with a malicious second factor name containing script tags or other executable code, this unescaped input gets rendered directly into the web page without proper sanitization. The vulnerability specifically targets the administrative interface where privileged users perform account management operations, making it particularly dangerous as it allows attackers to execute malicious scripts within the context of elevated administrator sessions.
The operational impact of this vulnerability extends beyond simple cross-site scripting by enabling sophisticated attack vectors that can escalate privileges and compromise entire administrative environments. When an administrator views the delete confirmation dialog for an attacker-controlled account, the malicious second factor name executes in their browser session, potentially allowing attackers to steal session cookies, perform unauthorized actions, or redirect administrators to malicious sites. This vulnerability aligns with CWE-79 which addresses cross-site scripting flaws and can be mapped to ATT&CK technique T1059.007 for script execution within web browsers. The attack requires minimal privileges as it exploits an existing administrative interface rather than requiring initial access through other means.
Administrative users who perform account deletion operations are particularly vulnerable since they must interact with the affected dialog. Attackers can craft malicious second factor names containing payloads such as javascript:alert(document.cookie) or more sophisticated XSS vectors that can persist across sessions. The vulnerability's exploitation becomes more severe when considering that administrators often have broad permissions including user management, content moderation, and system configuration capabilities. Once compromised, an attacker could potentially access sensitive user data, modify forum content, or manipulate system settings through the administrative account.
The fix implemented in versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5 involves proper input sanitization and output encoding of second factor names within the delete confirmation dialogs. This remediation ensures that any user-controlled data is properly escaped before rendering in web contexts, preventing script execution in administrator browsers. Organizations should prioritize updating to these patched versions immediately while also implementing additional monitoring for suspicious account creation or modification activities. Security teams should also consider deploying content security policies and regular vulnerability scanning to detect similar encoding flaws in other parts of their Discourse installations. The fix addresses the core issue by applying proper HTML escaping to all user-supplied data displayed in administrative interfaces, aligning with secure coding practices recommended in OWASP Top Ten and NIST cybersecurity guidelines for preventing cross-site scripting vulnerabilities.