CVE-2026-63171 in Agora Project
Summary
by MITRE • 10/14/2026
Omnispace Agora Project before 26.10.0 contains a stored cross-site scripting vulnerability that allows authenticated attackers to inject malicious script by submitting a crafted forum category description containing a double-quote character that breaks out of an HTML input value attribute. Attackers can exploit the HTMLPurifier configuration that preserves double-quotes to escape the attribute context and execute arbitrary script in the browser of users viewing the forum category.
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Analysis
by VulDB Data Team • 10/14/2026
The Omnispace Agora Project, specifically versions prior to 26.10.0, contains a critical stored cross-site scripting vulnerability within its forum module functionality. This security flaw arises from insufficient input validation and sanitization mechanisms when processing user-supplied data for forum category descriptions. The core technical issue lies in the interaction between how the application handles HTML attributes during rendering and the configuration of the underlying HTMLPurifier library used to sanitize content. When an authenticated attacker submits a crafted payload containing specific characters, such as double quotes, into the description field, the system fails to properly escape or encode these inputs before storing them in the database for later retrieval and display.
The exploitation mechanism relies on the fact that the application places user-controlled data directly within HTML input value attributes without adequate context-aware escaping. Although the project utilizes HTMLPurifier as a defense-in-depth measure against XSS, its configuration is set to preserve double-quote characters rather than encoding them into their corresponding HTML entities. This specific configuration choice allows an attacker to inject a payload that includes a closing double quote followed by malicious JavaScript code and potentially additional attribute injections or event handlers. By breaking out of the intended input value context, the injected script becomes part of the executable DOM structure when the page is rendered in a victim's browser.
This vulnerability classifies under CWE-79, known as Improper Neutralization of Input During Web Page Generation commonly referred to as Cross-site Scripting. The specific vector here represents Stored XSS because the malicious payload persists on the server side within the database and is subsequently served to multiple users over time. This persistence distinguishes it from reflected variants, significantly increasing its potential impact radius as every user who views the compromised forum category becomes a potential target for exploitation without requiring any immediate social engineering beyond accessing the specific page.
From an operational perspective, this vulnerability poses severe risks to data integrity and confidentiality within the Omnispace Agora environment. Successful exploitation allows attackers to execute arbitrary JavaScript in the context of the victim's browser session. This capability enables several malicious outcomes including session hijacking through theft of authentication cookies or tokens, credential harvesting by creating fake login forms that mimic legitimate interfaces, defacement of the user interface, and redirection of users to phishing sites. Since the attack requires only authenticated access to submit forum categories but affects any viewer regardless of their privilege level, it effectively allows lower-privileged users to impact higher-privileged administrators if they view the compromised content, thereby facilitating privilege escalation scenarios indirectly through session theft or manipulation.
The technical root cause is identified as CWE-601 URL Redirection to Untrusted Site which can lead to XSS and CWE-89 SQL Injection related input handling issues although in this specific case it is primarily an output encoding failure rather than a database injection issue. The vulnerability aligns with MITRE ATT&CK technique T1059 Command and Scripting Interpreter specifically JavaScript execution within the browser environment, allowing attackers to perform actions on behalf of victims such as T1078 Valid Accounts where stolen sessions are used for unauthorized access.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective solution is to upgrade the Omnispace Agora Project to version 26.10.0 or later, which presumably includes patches that correct the HTMLPurifier configuration or implement stricter output encoding practices. For organizations unable to immediately patch, implementing a Web Application Firewall rule set capable of detecting and blocking payloads containing unescaped double quotes within input value attributes can provide temporary protection. Additionally developers should enforce strict context-aware output encoding ensuring that all dynamic content inserted into HTML attributes is encoded using appropriate entity references such as converting double quotes to quot entities regardless of the sanitizer library settings. Input validation should also be strengthened to reject or sanitize special characters at the point of entry rather than relying solely on sanitization during rendering which can lead to inconsistencies and bypasses like this one.