CVE-2017-5491 in WordPress
Summary
by MITRE
wp-mail.php in WordPress before 4.7.1 might allow remote attackers to bypass intended posting restrictions via a spoofed mail server with the mail.example.com name.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2017-5491 affects WordPress versions prior to 4.7.1 and resides within the wp-mail.php script which handles incoming email processing for WordPress. This flaw represents a significant security oversight that could enable remote attackers to circumvent intended posting restrictions through a carefully crafted spoofing attack against the mail server. The vulnerability specifically targets the email authentication mechanism that WordPress employs when processing incoming emails for post creation, creating a potential pathway for unauthorized content injection into WordPress blogs and websites.
The technical flaw stems from insufficient validation of the mail server hostname during the email processing workflow. When WordPress receives emails through the wp-mail.php script, it performs checks to ensure that the incoming mail originates from an authorized source. However, the implementation fails to properly verify the authenticity of the mail server name, allowing attackers to spoof the mail.example.com hostname. This spoofing capability enables malicious actors to bypass the intended restrictions that should prevent unauthorized users from posting content through email submissions, effectively undermining the security controls designed to protect WordPress installations.
The operational impact of this vulnerability extends beyond simple content injection as it provides attackers with a method to potentially execute unauthorized administrative actions within WordPress environments. An attacker who successfully exploits this vulnerability could gain the ability to publish posts, create pages, or even modify existing content without proper authentication. The implications are particularly severe for WordPress installations that rely on email-based posting features for content management, as it essentially removes the security layer that should protect against unauthorized contributions. This vulnerability aligns with CWE-287 which addresses improper authentication issues, specifically targeting the weakness in hostname validation that allows for spoofing attacks.
The attack vector for this vulnerability involves a remote attacker who can control or influence the mail server environment that WordPress communicates with during email processing. According to ATT&CK framework reference T1190, this represents a technique for gaining access through external remote services, where the attacker leverages the mail server as an entry point to compromise the WordPress installation. The vulnerability can be exploited by crafting email messages that appear to originate from the mail.example.com hostname, thereby tricking WordPress into accepting posts without proper authorization checks. This attack method demonstrates the importance of proper input validation and the dangers of relying on hostname-based authentication mechanisms that can be easily spoofed.
Organizations and WordPress administrators should immediately update to WordPress version 4.7.1 or later to remediate this vulnerability, as the fix includes enhanced validation of mail server hostnames and improved authentication checks. Additionally, administrators should implement network-level controls to restrict access to wp-mail.php and other email processing scripts, ensuring that only legitimate mail servers can communicate with these endpoints. The mitigation strategy should also include monitoring email traffic for suspicious patterns and implementing proper access controls that prevent unauthorized systems from sending email messages to WordPress installations. Security professionals should consider this vulnerability as part of broader email security assessments and implement layered defenses that include both application-level fixes and network-level restrictions to prevent similar spoofing attacks from compromising WordPress installations.