CVE-2026-78003 in Mailgun for Plugin
Summary
by MITRE • 08/22/2026
The Mailgun for WordPress plugin for WordPress is vulnerable to Server-Side Request Forgery (SSRF) via path traversal in versions up to and including 2.2.0. This is due to insufficient input validation in the add_list() function, which accepts user-controlled array keys from $_POST['addresses'], passes them through sanitize_text_field(). This makes it possible for unauthenticated attackers to make authenticated POST requests to any Mailgun API endpoint using the WordPress site's API key, including creating inbound email-forwarding routes that can intercept password reset emails, leading to administrator account takeover.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified in the Mailgun for WordPress plugin affects versions up to and including 2.2.0, representing a critical security flaw rooted in insufficient input validation within the add_list() function. This Server-Side Request Forgery (SSRF) vector allows unauthenticated attackers to manipulate how the application constructs API requests by exploiting path traversal techniques. The core technical failure lies in the handling of user-controlled array keys derived from the $_POST['addresses'] parameter. Although the plugin attempts to sanitize this input using the WordPress function sanitize_text_field(), this measure is inadequate for preventing SSRF attacks because it does not restrict or validate the structure of the data against malicious payloads designed to alter request paths or parameters. Consequently, an attacker can inject specific sequences that bypass standard validation checks, effectively tricking the server into making authenticated POST requests to arbitrary Mailgun API endpoints using the legitimate WordPress site's stored API credentials.
The operational impact of this vulnerability is severe due to its unauthenticated nature and the high privileges associated with the compromised API key. By leveraging the SSRF flaw, an attacker can interact directly with the Mailgun infrastructure on behalf of the victim website. This capability extends beyond simple data exfiltration; it allows for active manipulation of email routing configurations. Specifically, attackers can create inbound email-forwarding routes that redirect sensitive communications intended for legitimate users to addresses controlled by the adversary. The most critical consequence of this control is the interception of password reset emails sent by WordPress or associated services. Since these emails typically contain time-sensitive tokens required to regain access to user accounts, their interception enables a direct path to account compromise without requiring any prior authentication credentials from the attacker.
This attack scenario aligns with several established cybersecurity frameworks and standards. The vulnerability is classified under CWE-918, which addresses Server-Side Request Forgery (SSRF), specifically highlighting the weakness in server-side input validation that allows an actor to influence the content or destination of requests made by a web application. Furthermore, the exploitation technique maps to MITRE ATT&CK techniques related to Resource Hijacking and Credential Access. The act of creating inbound routes corresponds to T1508 (Exploitation for Defense Evasion) if used to hide malicious activity, but more directly relates to T1539 (Steal Web Session Cookie) or T1114 (Email Collection) when considering the interception aspect. However, the primary mechanism of account takeover via intercepted password resets is a classic example of Credential Access through phishing-like mechanisms facilitated by server-side manipulation, falling under the broader category of Initial Access and Persistence if the attacker maintains control over the compromised accounts for further lateral movement within the organization's digital ecosystem.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The most effective solution is to upgrade the Mailgun for WordPress plugin to a version newer than 2.2.0, where developers have presumably implemented stricter input validation and output encoding practices that prevent path traversal and SSRF payloads from being processed correctly. In addition to updating software, administrators should enforce strict API key permissions by adhering to the principle of least privilege, ensuring that keys used for routine operations do not possess excessive rights such as creating routes or modifying domain settings unless absolutely necessary. Implementing a Web Application Firewall (WAF) with rules specifically tuned to detect SSRF patterns and path traversal sequences can provide an additional layer of defense against exploitation attempts. Furthermore, organizations should monitor Mailgun API logs for unusual activity, such as the creation of new inbound routes or unexpected spikes in outbound email traffic, which may indicate that a vulnerability has been successfully exploited. Regular security audits and code reviews focusing on how external inputs are handled before being passed to internal APIs are essential to preventing similar vulnerabilities from persisting in WordPress ecosystems.