CVE-2026-1877: Auto Post Scheduler Plugin CSRF Vulnerability

CVE-2026-1877 Overview

The Auto Post Scheduler plugin for WordPress is vulnerable to Cross-Site Request Forgery (CSRF) in all versions up to and including 1.84. This vulnerability exists due to missing nonce validation on the aps_options_page function, which allows unauthenticated attackers to update plugin settings and inject malicious web scripts via a forged request. Successful exploitation requires tricking a site administrator into performing an action such as clicking on a malicious link.

Critical Impact

Attackers can modify plugin settings and inject malicious scripts into WordPress sites by exploiting the missing CSRF protection, potentially leading to stored Cross-Site Scripting (XSS) attacks affecting all site visitors.

Affected Products

• Auto Post Scheduler plugin for WordPress versions up to and including 1.84

Discovery Timeline

• 2026-03-31 - CVE-2026-1877 published to NVD
• 2026-04-01 - Last updated in NVD database

Technical Details for CVE-2026-1877

Vulnerability Analysis

This vulnerability combines two distinct weaknesses: Cross-Site Request Forgery (CSRF) and stored Cross-Site Scripting (XSS). The aps_options_page function in the Auto Post Scheduler plugin lacks proper nonce validation, which is WordPress's standard mechanism for protecting against CSRF attacks. Without this validation, the plugin cannot verify that form submissions originate from legitimate, authenticated user sessions.

The missing nonce check enables attackers to craft malicious requests that, when executed by an authenticated administrator, modify the plugin's settings. The secondary impact occurs because the plugin also fails to properly sanitize input values before storing them, allowing malicious JavaScript to be injected into the settings. This stored XSS payload then executes whenever the affected pages are loaded by any user.

Root Cause

The root cause of this vulnerability is the absence of nonce verification in the aps_options_page function. WordPress provides the wp_verify_nonce() and check_admin_referer() functions specifically to prevent CSRF attacks by validating that requests include a valid, time-limited security token. The vulnerable code at lines 200 and 962 of auto-post-scheduler.php processes settings updates without checking for these security tokens, creating an exploitable condition.

Attack Vector

The attack requires social engineering to trick a logged-in WordPress administrator into visiting a malicious webpage or clicking a crafted link. The attacker's page contains a hidden form that automatically submits a request to the vulnerable WordPress site's aps_options_page endpoint. Because the administrator's browser includes their authentication cookies with the request, and the plugin doesn't validate a nonce, the malicious settings update succeeds.

The attack can be delivered through various vectors including phishing emails, malicious advertisements, compromised websites, or social media links. Once the administrator's browser executes the forged request, the attacker's malicious JavaScript payload is stored in the plugin settings and will execute in the context of any user who views affected admin pages.

Detection Methods for CVE-2026-1877

Indicators of Compromise

• Unexpected changes to Auto Post Scheduler plugin settings without administrator action
• Presence of JavaScript code or <script> tags within plugin configuration values
• Administrator reports of clicking suspicious links prior to observed anomalies
• Browser console errors or unexpected script execution on WordPress admin pages

Detection Strategies

• Review Auto Post Scheduler plugin settings for any malicious JavaScript or HTML injection
• Audit web server access logs for POST requests to wp-admin/options-general.php with Auto Post Scheduler parameters from unexpected referrers
• Monitor WordPress database entries in the wp_options table for aps_ prefixed options containing suspicious content
• Deploy Web Application Firewalls (WAF) with rules to detect CSRF attack patterns targeting WordPress plugins

Monitoring Recommendations

• Implement real-time monitoring of WordPress admin settings changes with alerts for unexpected modifications
• Configure logging for all administrative actions within WordPress using security plugins
• Enable browser Content Security Policy (CSP) headers to mitigate impact of successful XSS injection
• Regularly review plugin configurations as part of security audit procedures

How to Mitigate CVE-2026-1877

Immediate Actions Required

• Update the Auto Post Scheduler plugin to a version newer than 1.84 that includes CSRF protection
• If an update is not available, consider temporarily deactivating the plugin until a patch is released
• Review current plugin settings for any signs of malicious content injection
• Educate WordPress administrators about the risks of clicking unknown links while logged into the admin panel

Patch Information

Organizations should monitor the WordPress Plugin Repository and the Wordfence Vulnerability Report for updates regarding a patched version of the Auto Post Scheduler plugin. The fix should implement proper nonce validation using WordPress security functions like wp_verify_nonce() or check_admin_referer() in the aps_options_page function.

Workarounds

• Implement additional authentication requirements for WordPress administrators (e.g., IP restrictions, VPN access)
• Use a Web Application Firewall to filter malicious requests targeting the vulnerable endpoint
• Consider using alternative scheduling plugins that have proper CSRF protections until the vulnerability is patched
• Configure browsers with extensions that block automatic form submissions from untrusted domains

# Configuration example
# Add to WordPress .htaccess to restrict admin access by IP
<Files "options-general.php">
    Order Deny,Allow
    Deny from all
    Allow from 192.168.1.0/24
    Allow from 10.0.0.0/8
</Files>