Vulnerability Advisory — Recurring PayPal Donations Plugin (≤ 1.8): Cross‑Site Scripting (XSS) — CVE‑2025‑57891

Published: 22 August 2025
Reported: 15 July 2025 (researcher: Nabil Irawan)
Severity: Low (CVSS 5.9)
Required privilege to trigger: Administrator
Fixed in: 1.9

This advisory explains a stored Cross‑Site Scripting (XSS) vulnerability affecting versions 1.8 and earlier of the “Recurring PayPal Donations” WordPress plugin (CVE‑2025‑57891). It is written from the perspective of a Hong Kong security expert and targets site administrators, developers and incident responders: how the issue works, how to detect exploitation, immediate mitigations you can apply, and secure coding fixes plugin authors should implement.

Executive summary

• What happened: A stored XSS vulnerability was found in Recurring PayPal Donations (≤ 1.8). Administrator‑entered content is stored and later rendered without sufficient escaping or filtering, allowing injected HTML/JavaScript to run in the context of visitors and administrators.
• Risk: Low (CVSS 5.9) — exploitation requires Administrator privileges to insert payloads. Nonetheless, XSS can lead to session theft, redirecting donations, defacement, or client‑side payload delivery.
• Immediate fix: Upgrade the plugin to version 1.9 (or later) which includes the security fix.
• Interim mitigations: If updating is not immediately possible, apply targeted mitigations: virtual patching with a WAF, strict Content Security Policy (CSP) headers, sanitise stored data via maintenance scripts, and reduce admin exposure (IP restrictions, MFA).

How this XSS works — technical overview

Analysis shows the issue is a stored XSS originating from admin‑entered content that is later output without proper escaping. Common affected fields in donation plugins include donation descriptions, thank‑you messages, receipt templates, or custom HTML fields. If these values are stored and printed using raw echo/print without esc_html(), esc_attr(), wp_kses() or equivalent, injected scripts will execute in the browser of any visitor who views the affected output.

Because the attacker must have Administrator privileges to save the content, this is not an unauthenticated remote RCE. However, stolen or compromised admin accounts, rogue insiders, or insecure developer credentials can be used to plant persistent payloads that then affect site visitors and other administrators.

Key indicators:

• The plugin stores user content (options or postmeta) and later outputs it without escaping.
• The plugin accepts input fields where HTML is permitted and does not apply sanitisation on save or escaping on render.

Reproduction (high level)

Exploit code is not published here. High‑level reproduction steps an administrator could follow:

1. Log in to WP Admin as an Administrator.
2. Open the Recurring PayPal Donations plugin settings or UI that accepts free text/custom messages.
3. Enter HTML/JavaScript into a field that persists (e.g., donation message, thank you page content).
4. Save settings; the content is stored in options/postmeta.
5. A visitor or another admin views the frontend or plugin preview where the content is rendered; the malicious script executes.

The payload persists until removed, potentially affecting multiple visitors and admins.

Immediate actions for site administrators (priority order)

1. Upgrade to plugin version 1.9 or later.
   This is the definitive fix from the plugin author. Schedule and perform the update during an appropriate maintenance window.
2. If you cannot update immediately, apply temporary mitigations:
   • Deploy a targeted WAF rule (virtual patch) to block common XSS payloads against the plugin’s admin endpoints.
   • Restrict wp‑admin and plugin settings pages by IP or require VPN access where feasible.
   • Enforce strong admin account hygiene: rotate admin passwords, enable multi‑factor authentication, and audit admin users for unknown accounts.
   • Add a strict Content Security Policy (CSP) to reduce impact of inline scripts (test thoroughly to avoid breaking functionality). Example minimal header:
     Content-Security-Policy: default-src 'self'; script-src 'self' https://trusted.paypal.com; object-src 'none'; base-uri 'self';
3. Search for and remove malicious stored content:
   • Scan options and postmeta for <script> tags and suspicious external domains before making changes to production.
   • Use read‑only database queries first and maintain backups before editing.
4. Monitor and notify:
   • Review webserver logs for suspicious POSTs to admin endpoints and requests containing suspicious payloads.
   • Notify internal teams; if compromise is suspected, escalate to incident response.

Detection: how to tell if your site was exploited

Look for:

• Unexpected <script> tags or inline scripts in pages that previously contained plain text (donation descriptions, receipts).
• Redirects from donation pages to unfamiliar domains or altered PayPal links.
• New or modified admin pages, posts, or options containing HTML/JS.
• New administrator accounts or changes to existing accounts.
• Outgoing connections from the server to unfamiliar domains.
• Browser console errors referencing inline scripts where none existed before.

Automated checks (examples):

SELECT option_name, LENGTH(option_value) as L, option_value
FROM wp_options
WHERE option_value LIKE '%<script%';

grep -R --exclude-dir=wp-content/uploads -n "<script" /var/www/html

find /var/www/html -type f -mtime -7 -print

If exploitation is detected: contain first (maintenance mode or offline), preserve evidence, and follow incident response steps below.

Incident response (recommended steps)

1. Contain: Enable maintenance mode or restrict admin access by IP. Preserve logs and evidence.
2. Preserve evidence: Create full forensic backups of files and the database; export webserver access and error logs.
3. Eradicate:
   • Remove malicious content from database and files.
   • Disable the affected plugin if you cannot update immediately.
   • Revoke and rotate all administrator passwords and API keys (including PayPal credentials if relevant).
   • Inspect for webshells or backdoors in uploads, plugin and theme directories.
4. Recover:
   • Upgrade the plugin to 1.9 or later.
   • Restore clean backups if necessary.
   • Rebuild admin accounts only after forensic review.
5. Post‑incident: Enforce MFA for all admin users, increase monitoring, schedule regular scans, and perform a root cause analysis (RCA).

Suggested virtual patch / WAF rules (examples)

Below are generic rule examples to help create targeted virtual patches. Tune these to your environment and test in monitoring mode before blocking to avoid false positives. Replace field names with actual plugin parameter names (for example: donation_message, receipt_text).

ModSecurity (Apache) example — basic XSS detection in request parameters:

# Block suspicious script tags and inline event handlers in request fields
SecRule ARGS_NAMES|ARGS "@rx (?:<\s*script\b|javascript:|on\w+\s*=)" \
    "id:1001001,phase:2,deny,status:403,log,msg:'Potential XSS - blocking request',severity:2"

More specific rule targeting plugin admin pages (only block when URI contains the plugin slug):

SecRule REQUEST_URI "@contains recurring-donation" "phase:1,id:1001002,pass,nolog,chain"
  SecRule ARGS "@rx (?:<\s*script\b|javascript:|on\w+\s*=)" "id:1001003,phase:2,deny,log,msg:'WAF: recurring-donation XSS attempt'"

Nginx (ngx_lua) example — block requests with script tags:

# inside server/location
access_by_lua_block {
  local args = ngx.req.get_uri_args()
  local suspicious = false
  for k, v in pairs(args) do
    if type(v) == "table" then
      v = table.concat(v, " ")
    end
    if v:lower():find("<script") or v:lower():find("javascript:") or v:lower():find("on%w+=") then
      suspicious = true
      break
    end
  end
  if suspicious then
    ngx.log(ngx.ERR, "Blocked suspicious XSS request")
    return ngx.exit(403)
  end
}

WordPress‑level hardening (PHP hook) — sanitize incoming options before saving:

add_filter( 'pre_update_option_recurring_donation_custom_message', function( $new_value, $old_value, $option ) {
    // Strip scripts; allow limited HTML if needed.
    return wp_kses( $new_value, array(
        'a' => array( 'href' => true, 'title' => true ),
        'strong' => array(), 'em' => array(), 'p' => array()
    ) );
}, 10, 3 );

These are starting points. Where possible, scope rules to requests targeting the vulnerable plugin pages and include only clearly suspicious payloads to reduce false positives.

Fixes plugin developers must implement

1. Validate input on save: Use sanitize_text_field(), sanitize_email(), sanitize_hex_color(), intval(), or wp_kses() depending on expected input. If admin HTML is intended, restrict it with wp_kses() and a strict allowed tags list.
2. Escape output on render: Use esc_html(), esc_attr(), esc_url(), or wp_kses_post() when printing content. Escape at render time even for “trusted” admin inputs.
3. Capability checks and nonces: Verify current_user_can( ‘manage_options’ ) or equivalent before processing settings. Use wp_nonce_field() and check_admin_referer() to mitigate CSRF.
4. Store structured data: Prefer structured arrays or keyed objects instead of arbitrary HTML blobs where possible.
5. Unit tests and security review: Add tests ensuring HTML tags are properly escaped/filtered in outputs. Include static analysis and threat modelling in development lifecycle.

Example secure save handler:

if ( isset( $_POST['recurring_message'] ) && current_user_can( 'manage_options' ) ) {
    check_admin_referer( 'recurring_save_settings', 'recurring_nonce' );
    $clean = wp_kses( wp_unslash( $_POST['recurring_message'] ), array(
        'a' => array( 'href' => true, 'title' => true ),
        'strong' => array(), 'em' => array(), 'p' => array()
    ) );
    update_option( 'recurring_message', $clean );
}

Rendering safely:

echo wp_kses_post( get_option( 'recurring_message' ) ); // already cleaned, but safe double-check

Long‑term security recommendations for site owners

• Keep WordPress core, plugins and themes updated promptly.
• Limit Administrator accounts to those who truly need full privileges; use Editor/Author roles where possible.
• Enforce multi‑factor authentication for all privileged accounts.
• Harden wp‑admin access via IP whitelisting or VPN for administrators.
• Deploy WAF rules or virtual patching between disclosure and patching to reduce exposure.
• Enable file integrity monitoring and scheduled malware scans.
• Back up site and database regularly and verify restore procedures.
• Monitor application logs and set alerts for suspicious POST requests or unusual URIs.

Example search queries and commands for responders

SELECT option_name, option_value FROM wp_options WHERE option_value LIKE '%<script%';
SELECT meta_id, meta_key, meta_value FROM wp_postmeta WHERE meta_value LIKE '%<script%';

grep -R --exclude-dir=wp-content/uploads -n "<script" wp-content/plugins wp-content/themes

SELECT ID, user_login, user_registered FROM wp_users WHERE user_registered > DATE_SUB(NOW(), INTERVAL 30 DAY);

find /var/www/html -type f -mtime -30 -ls

FAQ

Q: My site uses this plugin but I don’t see signs of compromise. What should I do?
A: Update the plugin to 1.9 immediately. Then perform detection checks listed above (database search for <script> tags, recent logins, new admin users). Continue monitoring logs for unusual activity.

Q: Does this vulnerability allow attackers to run arbitrary code on the server?
A: No. This is a client‑side XSS issue: JavaScript executes in visitors’ browsers, not on the server. However, XSS can facilitate session theft which could lead to server‑side changes.

Q: My WordPress site uses a managed firewall. Am I safe?
A: A managed WAF can significantly reduce risk if it provides timely virtual patching. However, WAF rules must be tuned to the specific vectors; plugin updates are still necessary and should be applied.

Timeline & credit

• Reported by researcher: Nabil Irawan — 15 July 2025
• Public advisory published: 22 August 2025
• CVE assigned: CVE‑2025‑57891
• Fixed in Recurring PayPal Donations plugin: version 1.9

We thank the researcher for responsible disclosure and encourage plugin developers to adopt the secure coding patterns described above.

Closing recommendations — what to do now

1. Update Recurring PayPal Donations to version 1.9 immediately.
2. If you cannot update now, deploy targeted virtual patches / WAF rules, restrict admin access by IP, and enforce MFA.
3. Search database and files for injected scripts and suspicious entries; remove or restore from clean backups if active malicious content is found.
4. Harden admin account security and rotate credentials.
5. Consider adding a CSP to reduce impact of inline scripts and schedule regular malware scans.

XSS issues such as CVE‑2025‑57891 are straightforward to remediate but can be leveraged into larger compromises if administrative access is weak. Patch promptly, harden admin controls, and maintain layered protections to reduce both likelihood and impact of exploitation.