CVE-2026-85676 in Dub
Summary
by MITRE • 09/04/2026
Dub contains an open redirect vulnerability in the redir_url query parameter that is accepted on every short link without validation or domain allowlist enforcement. Attackers can append the redir_url parameter to any short link to redirect visitors to arbitrary external URLs through the trusted Dub domain, bypassing destination blacklists and potentially enabling phishing attacks with link cloaking enabled.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified in Dub represents a critical open redirect flaw rooted in insufficient input validation within the application's URL redirection logic. Specifically, the redir_url query parameter is processed without any form of domain allowlisting or strict validation mechanisms. This architectural oversight allows an attacker to inject arbitrary external URLs into the request stream, which the server then processes and redirects users toward without verifying if the destination falls within a trusted set of domains. The absence of such controls means that every short link generated by the platform can be manipulated to serve as a vector for malicious redirection, fundamentally undermining the integrity of the URL shortening service.
From an operational perspective, this flaw enables attackers to bypass existing security measures designed to prevent abuse, such as destination blacklists. By leveraging the trusted reputation of the Dub domain, adversaries can cloak their phishing links behind legitimate-looking URLs that originate from a known and trustworthy source. This technique significantly increases the likelihood of successful social engineering attacks, as users are more inclined to trust links associated with reputable platforms. The ability to redirect traffic to arbitrary external sites facilitates credential harvesting, malware distribution, and other malicious activities under the guise of safe browsing experiences.
This vulnerability aligns closely with CWE-601, which defines URL Redirection to Untrusted Site (Open Redirect). It also maps to MITRE ATT&CK technique T1583.002, specifically Acquire Infrastructure: Domains, where attackers register or compromise domains to lend credibility to their campaigns. In the context of Dub, while no new infrastructure is registered by the attacker in terms of hosting malicious content, they are effectively abusing existing trusted infrastructure for redirection purposes. This abuse allows them to evade security filters that rely on domain reputation scores and blacklists, as the initial click occurs on a whitelisted domain before being forwarded to the potentially harmful destination.
To mitigate this risk, it is imperative to implement strict validation rules for all redirect parameters. The application should enforce an allowlist of approved domains or validate that the target URL belongs to a predefined set of trusted entities. Alternatively, implementing relative path redirections where possible can reduce exposure to external domain manipulation. Additionally, integrating security headers such as Content Security Policy with directives limiting frame ancestors and script sources may provide supplementary protection against certain exploitation vectors associated with open redirects. Regular code audits focusing on input validation and output encoding are essential to prevent similar vulnerabilities in future updates.