CVE-2026-75908 in Newsletters Plugin
Summary
by MITRE • 08/25/2026
The Newsletters plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 4.17. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for authenticated attackers, with author-level access and above, to send arbitrary newsletter emails to users of any WordPress role, including administrators, by forging POST fields during a normal post submission. This allows an attacker-supplied role slug via the newsletters_mailinglistsroles POST field to be passed directly to get_users(), enabling unauthorized mass-mailing and potential phishing against privileged site users through the site's own outbound email channel.
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Analysis
by VulDB Data Team • 08/25/2026
The Newsletters plugin for WordPress, specifically in versions up to and including 4.17, contains a critical authorization bypass vulnerability that undermines the intended access control mechanisms of the application. This flaw stems from insufficient verification of user privileges when processing newsletter mailing operations. While the vulnerability requires an authenticated attacker with at least author-level permissions to exploit, this threshold is relatively low within many WordPress environments where content creation roles are commonly assigned. The core technical failure lies in how the plugin handles input data during the submission of a new post or newsletter draft. Instead of strictly validating that the requested recipient list aligns with the sender's authorized scope, the application directly processes user-supplied role slugs from POST fields without adequate sanitization or authorization checks against the current user's actual capabilities.
The technical mechanism of this exploit involves manipulating specific form parameters during a standard post submission workflow. An attacker can forge HTTP POST requests to include arbitrary values in the newsletters_mailinglistsroles field. These forged values are passed directly into WordPress functions such as get_users(), which then resolves these role slugs to identify target recipients. Because there is no intermediate validation step to ensure that an author-level user has permission to send emails to higher-privileged roles, such as administrators or editors, the system proceeds with dispatching the email. This effectively bypasses the intended restriction where lower-tier users should only be able to notify peers of similar privilege levels, thereby allowing lateral movement in terms of communication reach within the site's ecosystem.
The operational impact of this vulnerability is significant due to its potential for abuse as a vector for phishing and social engineering attacks. By leveraging the legitimate outbound email channel of the WordPress installation, an attacker can send arbitrary newsletter emails to any user on the platform, including those with administrative privileges. This creates a high-fidelity attack surface because recipients are likely to trust messages appearing to originate from their own organization's internal systems rather than external sources. The ability to mass-mail privileged users increases the likelihood of successful credential harvesting or malware distribution if malicious links or attachments are included in the forged newsletters. Furthermore, this abuse can lead to reputational damage for the site owner and potential compliance violations depending on the sensitivity of the information disseminated through these unauthorized communications.
From a classification perspective, this vulnerability aligns with CWE-285, which describes Improper Authorization, as the application fails to enforce proper access controls when granting users permission to perform actions. It also relates closely to CWE-913, specifically concerning improper control of frequency-limit or rate limiting if used for mass mailing, though the primary issue is authorization rather than resource exhaustion. In terms of offensive security frameworks, this exploit maps to MITRE ATT&CK techniques involving Initial Access and Execution via trusted relationships, as well as Command and Control through legitimate application channels. The attacker leverages existing credentials and trust within the WordPress environment to execute actions that should be restricted by role-based access control policies.
Mitigation strategies must address both immediate remediation and long-term security posture improvements. The most effective solution is to upgrade the Newsletters plugin to a version later than 4.17, where developers have presumably implemented stricter input validation and authorization checks for recipient selection fields. For organizations unable to update immediately due to compatibility constraints, temporary mitigations should include restricting author-level access to only those users who absolutely require newsletter publishing capabilities. Additionally, implementing Web Application Firewall rules that monitor for anomalous POST payloads containing unexpected role slugs in the newsletters_mailinglistsroles field can provide a layer of defense-in-depth. Security teams should also audit user roles across their WordPress installations to ensure that minimum privilege principles are enforced, reducing the pool of potential attackers who possess author-level access or higher. Regular monitoring of outbound email logs for unusual patterns or high volumes of messages sent by lower-privileged accounts can aid in early detection of exploitation attempts.