CVE-2026-90453 in Malcolm
Summary
by MITRE • 09/12/2026
A file-upload handler redirects the authenticated client's browser to a URL taken directly from that same request's Referer header, without validating it against the application's own origin. This allows an authenticated attacker to craft a request that causes another user's browser to be redirected to an arbitrary external destination after completing an upload.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/12/2026
The vulnerability described constitutes an Unvalidated Redirect and Forward flaw, specifically manifesting as an Open Redirect within the context of a file-upload operation. This security weakness arises from a fundamental failure in input validation where the application trusts user-supplied data without sufficient scrutiny. In this specific scenario, the server-side handler retrieves the Referer header value directly from the HTTP request and uses it to construct a redirect response for the authenticated client's browser. The critical technical flaw lies in the absence of any mechanism to verify that the destination URL belongs to an expected domain or origin. By relying on the Referer header, which is easily spoofable by clients, the application inadvertently creates a pathway for attackers to manipulate navigation flows. This behavior violates standard security practices regarding state management and session handling during file uploads, where trust boundaries are often blurred between client-provided metadata and server-side logic.
From an operational perspective, this vulnerability allows an authenticated attacker to exploit the redirect mechanism to perform phishing attacks or drive-by downloads against other users of the application. Since the redirection occurs after a successful upload operation, it may appear legitimate to the victim user who just completed their task. An attacker can craft a malicious request containing a Referer header pointing to a fraudulent site that mimics the login page of the target organization or hosts malware. When another authenticated user submits this crafted request, their browser is redirected away from the application's trusted domain without warning. This disruption not only degrades the user experience but also facilitates social engineering attacks where users might inadvertently enter credentials into a fake portal or download malicious payloads under the guise of completing their upload task. The impact is particularly severe because it leverages existing authentication sessions, making the attack appear more trustworthy than standard external phishing links.
This vulnerability aligns with Common Weakness Enumeration (CWE) ID 601, which defines URL Redirection to Untrusted Site via User-Input in a Redirect Parameter. Although CWE 601 typically refers to explicit redirect parameters like url or dest, the principle applies equally here as the Referer header is effectively being used as an implicit control parameter for navigation logic. Furthermore, this flaw maps directly to the MITRE ATT&CK technique T1583.002, which covers Acquire Infrastructure: Domains under the broader category of Resource Development. Attackers utilize such vulnerabilities to establish credible footholds by making malicious links appear legitimate through trusted domains. The exploitation chain involves crafting a request with a spoofed Referer header pointing to attacker-controlled infrastructure and inducing an authenticated victim to execute it via social engineering or cross-site scripting if other vectors exist.
To mitigate this vulnerability, the application must implement strict validation for all redirect destinations. Developers should maintain a whitelist of allowed domains that are permitted as redirect targets rather than relying on negative filtering which can be bypassed through encoding tricks or subdomain variations. If dynamic redirects are necessary, they should use internal identifiers mapped to safe URLs in a server-side database instead of accepting raw URL strings from user input. Additionally, the application should avoid using the Referer header for any security-critical logic such as navigation control, as this header is optional and easily manipulated by clients or intermediate proxies. Implementing SameSite cookie attributes can also help mitigate some forms of cross-site request forgery that might accompany these redirects, although it does not directly prevent open redirect vulnerabilities. Regular code reviews focusing on input validation patterns and automated static analysis tools configured to detect CWE 601 instances are essential for preventing such flaws in future development cycles.