The Post SMTP plugin for WordPress is vulnerable to unauthorized modification of data due to a missing capability check on the `handle_office365_oauth_redirect()` function in all versions up to, and including, 3.8.0. This is due to the function being hooked to `admin_init` without any `current_user_can()` check or nonce verification. This makes it possible for authenticated attackers, with Subscriber-level access and above, to overwrite the site's Office 365 OAuth mail configuration (access token, refresh token, and user email) via a crafted URL. The configuration option is used during wizard setup of Microsoft365 SMTP, only available in the Pro option of the plugin. This could cause an Administrator to believe an attacker-controlled Azure app is their own, and lead them to connect the plugin to the attacker's account during configuration after upgrading to Pro.
CVE-2026-2559 is a medium severity with CVSS 5.3 Vulnerability issue affecting the Plugin Post SMTP – Complete Email Deliverability and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App. It affects Versions up to 3.8.0 and is fixed in 3.9.0.
CVE-2026-2559 is tracked for the Plugin Post SMTP – Complete Email Deliverability and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App as medium severity with CVSS 5.3. The affected range is Versions up to 3.8.0. Update Post SMTP – Complete Email Deliverability and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App to 3.9.0 or newer where that version is compatible with the site.
| Software Type | Plugin |
|---|---|
| Software Slug |
post-smtp
View on wordpress.org
|
| CVE | CVE-2026-2559 |
| Patched Versions |
3.9.0
|
| Affected Versions |
Versions up to 3.8.0
|
These internal links group the same WordPress plugin by CVE, issue type, severity, and patch status so operators and search engines can connect the full vulnerability cluster.
Post SMTP – Complete SMTP Solution with Logs, Alerts, Backup SMTP & Mobile App <= 3.6.0 - Missing Authorization to Account Takeover via Unauthenticated Email Log Disclosure
POST SMTP Mailer – Email log, Delivery Failure Notifications and Best Mail SMTP for WordPress <= 2.8.7 - Authorization Bypass via type connect-app API
Post SMTP <= 3.2.0 - Missing Authorization to Authenticated (Subscriber+) Account Takeover via Email Log Exposure
Post SMTP <= 3.8.0 - Unauthenticated Stored Cross-Site Scripting via 'event_type'
Post SMTP <= 3.0.2 - Unauthenticated Stored Cross-Site Scripting
POST SMTP Mailer – Email log, Delivery Failure Notifications and Best Mail SMTP for WordPress <= 2.9.3 - Authenticated (Administrator+) SQL Injection
POST SMTP Mailer – Email log, Delivery Failure Notifications and Best Mail SMTP for WordPress <= 2.8.7 - Unauthenticated Stored Cross-Site Scripting via device
POST SMTP Mailer – Email log, Delivery Failure Notifications and Best Mail SMTP for WordPress <= 2.8.6 - Authenticated (Administrator+) SQL Injection
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