CVE-2026-63169 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 users to post messages containing attacker-controlled iframes through the messenger's HTMLPurifier SafeIframe branch. Attackers can craft a message with a malicious iframe that is stored and automatically rendered to other channel members, enabling zero-click drive-by downloads and framed JavaScript execution in recipients' browsers.
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Analysis
by VulDB Data Team • 10/14/2026
The Omnispace Agora Project prior to version 26.10.0 suffers from a critical Stored Cross-Site Scripting vulnerability within its messaging subsystem. This flaw specifically resides in the HTMLPurifier SafeIframe branch, which is designed to sanitize user-supplied content by allowing only safe iframe elements while stripping out potentially dangerous tags and attributes. However, the implementation fails to adequately restrict or validate the properties of these allowed iframes, creating a significant security gap that allows authenticated users to inject malicious payloads into stored messages. The vulnerability arises because the sanitization logic permits the inclusion of iframe elements but does not sufficiently constrain their source URLs or execution contexts, thereby enabling an attacker to embed arbitrary HTML content that persists in the application's database and is subsequently served to other users without further filtering.
From a technical perspective, this flaw represents a classic case of insufficient validation within a whitelist-based sanitization strategy. While allowing specific tags like iframes can be necessary for legitimate functionality such as embedding videos or maps, it requires rigorous control over all attributes associated with those tags. In this instance, the application allows authenticated users to post messages containing attacker-controlled iframe elements. When another user views the channel where these messages are posted, the browser automatically renders the stored HTML content. Because the malicious iframes are not stripped out during the rendering process, they execute within the context of the victim's session and origin. This mechanism effectively bypasses standard security controls that rely on input validation at the point of entry, as the data is considered trusted once it has been successfully stored in the database.
The operational impact of this vulnerability is severe due to its potential for zero-click exploitation against victims who simply view the affected channel. An attacker can craft a message containing an iframe pointing to a malicious server hosting drive-by download exploits or phishing pages. When a victim loads the page, the browser automatically executes the JavaScript within the framed content without any additional interaction from the user. This capability allows attackers to perform actions such as stealing session cookies, hijacking authenticated sessions, exfiltrating sensitive data visible on the current page via cross-origin requests if permissions allow, or redirecting users to malicious sites for credential harvesting. The persistence of the payload means that every new member joining the channel or any existing member refreshing their view becomes a potential target, amplifying the blast radius significantly compared to reflected XSS attacks which require immediate interaction with a specific link.
This vulnerability aligns closely with CWE-79, known as Improper Neutralization of Input During Web Page Generation commonly referred to as Cross-site Scripting. Specifically, it falls under stored variants where malicious scripts are permanently stored within target applications such as databases or message boards. In terms of the MITRE ATT&CK framework, this exploit maps to T1059 Command and Control via Application Layer Protocol for initial access if used in conjunction with other techniques, but more directly relates to TA0003 Persistence through Stored XSS payloads that remain active until removed by an administrator. The use of iframes also touches upon aspects of client-side code injection where the attacker leverages legitimate application features to execute unauthorized scripts within the user's browser environment.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary fix involves updating the Omnispace Agora Project to version 26.10.0 or later, which addresses this specific sanitization flaw in the HTMLPurifier configuration. For organizations unable to patch immediately, implementing a Web Application Firewall with rules capable of detecting and blocking iframe injection attempts can provide temporary protection. Additionally, developers should review all instances where user input is rendered as HTML and ensure that any allowed tags have their attributes strictly validated against a comprehensive whitelist. Enabling Content Security Policy headers with strict frame-ancestors directives can also mitigate the impact by preventing malicious sites from framing legitimate application pages or restricting which origins are permitted to embed content within the application, thereby reducing the effectiveness of drive-by download attempts and framed JavaScript execution attacks.