CVE-2026-1011 in 365
Summary
by MITRE • 01/16/2026
A stored cross-site scripting (XSS) vulnerability exists in the Altium Support Center AddComment endpoint due to missing server-side input sanitization. Although the client interface applies HTML escaping, the backend accepts and stores arbitrary HTML and JavaScript supplied via modified POST requests.
The injected content is rendered verbatim when support cases are viewed by other users, including support staff with elevated privileges, allowing execution of arbitrary JavaScript in the victim’s browser context.
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Analysis
by VulDB Data Team • 01/16/2026
This vulnerability represents a critical stored cross-site scripting flaw in the Altium Support Center application that fundamentally undermines user security and application integrity. The issue manifests specifically within the AddComment endpoint where the system fails to implement proper server-side input validation and sanitization mechanisms. While the client-side interface correctly applies HTML escaping to prevent immediate client-side exploitation, this protective measure proves insufficient as the backend component accepts and permanently stores malicious input without adequate filtering or sanitization. The vulnerability stems from a fundamental architectural oversight where the application assumes client-side protections are sufficient to prevent malicious data injection, creating a dangerous trust boundary failure that allows attackers to bypass intended security controls.
The technical exploitation of this vulnerability follows a well-defined attack pattern that aligns with CWE-79, which specifically addresses cross-site scripting vulnerabilities. Attackers can craft malicious POST requests containing HTML and JavaScript payloads that are subsequently stored within the application's database. When legitimate users, including support personnel with elevated privileges, view the support case containing the malicious comment, the stored content executes within their browser context without proper sanitization. This creates a persistent threat vector where malicious code can execute in the context of any user who accesses the affected support case, potentially enabling session hijacking, credential theft, or further escalation attacks. The vulnerability demonstrates a clear breakdown in the principle of least privilege as support staff with elevated access rights become potential targets for exploitation.
The operational impact of this vulnerability extends beyond simple data corruption or display issues, creating significant risks for both end users and organizational security. Support staff members who regularly access and review support cases become prime targets for attackers seeking to exploit their elevated privileges, potentially allowing unauthorized access to sensitive customer information or internal support systems. The stored nature of the vulnerability means that malicious payloads can persist for extended periods, providing attackers with ongoing access to victim systems. This vulnerability directly relates to ATT&CK technique T1531 which focuses on manipulation of external-facing applications, and T1059 which covers command and scripting interpreter usage. Organizations using Altium Support Center face potential data breaches, reputational damage, and regulatory compliance violations that could result from unauthorized access to support case information or user session compromise.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term architectural improvements. The primary fix involves implementing comprehensive server-side input validation and sanitization for all user-supplied content, particularly within endpoints that store data for later retrieval. This includes employing robust HTML sanitization libraries that can strip or escape dangerous elements such as script tags, event handlers, and other potentially malicious content before storage. Organizations should also implement Content Security Policy headers to provide additional defense-in-depth against XSS exploitation attempts. Regular security testing including automated scanning and manual penetration testing should be conducted to identify similar vulnerabilities in other application endpoints. The fix must also include proper input validation at multiple layers, ensuring that client-side protections are not relied upon exclusively for security, and that all data entering the application backend undergoes rigorous sanitization regardless of its source or intended use.