CVE-2026-81741 in Groundhogg Plugin
Summary
by MITRE • 09/09/2026
The Groundhogg — CRM, Newsletters, and Marketing Automation WordPress plugin before 4.7.2 does not restrict the redirect target of its email preference confirmation flow to the site's own host, allowing unauthenticated attackers to redirect visitors to an arbitrary external URL by way of a crafted link.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified in Groundhogg versions prior to 4.7.2 represents a critical Open Redirect flaw within the plugin’s email preference confirmation mechanism. This security deficiency stems from insufficient validation of user-supplied input used for determining post-action redirection targets. Specifically, when an unauthenticated visitor interacts with links designed to confirm their email preferences or update subscription statuses, the application accepts and processes redirect parameters without verifying that the destination URL resides on the same host as the WordPress site itself. This lack of domain restriction allows attackers to craft malicious URLs containing arbitrary external domains in the redirection parameter.
From a technical perspective, this flaw exploits the standard behavior of HTTP 3xx status codes used for redirects. When a user clicks a link generated by Groundhogg that includes a tampered redirect target, the web server issues an immediate response directing the browser to load content from a completely different domain controlled by the attacker. Because the initial request originates from a trusted and legitimate WordPress site, users are likely to trust the legitimacy of the action. The transition occurs seamlessly in the user’s browser address bar after the brief loading phase associated with the redirect, often bypassing visual cues that might otherwise alert cautious users to the change in domain context.
The operational impact of this vulnerability is primarily centered around social engineering and phishing attacks. Attackers can leverage this flaw to create highly convincing phishing pages by hosting malicious content on a lookalike or compromised external server while using the trusted Groundhogg URL as the entry point. This technique significantly increases the success rate of credential harvesting campaigns, malware distribution attempts, or other fraudulent activities because the initial link appears safe and authoritative. Furthermore, this vulnerability can be exploited to deface websites by redirecting traffic to pages containing malicious scripts that attempt to exploit browser vulnerabilities or manipulate session cookies if subsequent interactions occur on a trusted domain via cross-site scripting vectors facilitated through the redirected page.
This issue aligns with CWE-601, which defines Open Redirect as a type of vulnerability where an application redirects users to URLs provided by untrusted sources without proper validation. In terms of offensive security frameworks, this behavior corresponds to ATT&CK technique T1583.002, specifically Acquire Infrastructure: Domains, and is often utilized in conjunction with T1566.002 Spearphishing Link during the initial access phase of an attack chain. The exploitation requires no authentication, making it accessible to a wide range of threat actors seeking low-effort entry points into WordPress ecosystems that rely heavily on email marketing automation plugins like Groundhogg.
Mitigation strategies must prioritize immediate patching and defensive coding practices. Site administrators should upgrade the Groundhogg plugin to version 4.7.2 or later, where this validation logic has been corrected to enforce strict domain whitelisting for redirect targets. For environments where upgrading is not immediately feasible, temporary mitigations include implementing server-side rules using web application firewalls (WAFs) to detect and block requests containing suspicious query parameters indicative of open redirects. Additionally, developers should ensure that all future implementations of redirection logic strictly validate the host component of any URL against a predefined list of allowed domains or enforce same-origin policies before issuing HTTP redirect responses. Regular security audits focusing on input validation for navigation flows are essential to prevent similar vulnerabilities in other plugins and core functionalities within the WordPress ecosystem.