Urgent: Bold Page Builder (≤ 5.5.2) — Stored XSS (CVE-2025-66057)

Published: 27 November 2025   |   Author: Hong Kong Security Expert

A security researcher disclosed a stored Cross-Site Scripting (XSS) vulnerability affecting Bold Page Builder versions ≤ 5.5.2 (CVE-2025-66057). A low-privilege user (Contributor-level) can inject HTML/JavaScript that is stored and later executed in visitors’ browsers — including administrators. Although vendor fixes are available in 5.5.3, many sites remain unpatched or cannot immediately update due to compatibility concerns. This advisory explains the risk, root cause, detection methods, containment, technical mitigations (including WAF rules and virtual patching examples), and recovery steps in a straightforward, practical manner.

Executive summary — TL;DR

• Vulnerability: Stored Cross-Site Scripting (XSS) in Bold Page Builder ≤ 5.5.2 (CVE-2025-66057).
• Impact: Arbitrary JavaScript/HTML injection — possible session theft, account takeover, drive-by redirects, malicious content injection, SEO damage.
• Privilege required: Contributor (low-level); common in many WordPress sites.
• CVSS: 6.5 (medium). Labels don’t tell the whole story — contextual risk matters.
• Immediate action: Update to 5.5.3 or later as soon as practicable. If you can’t update immediately, apply mitigations below (restrict editing, scan content, apply WAF/virtual patching).

Why this XSS matters even if it’s “low priority”

CVSS scores are a triage tool, but stored XSS deserves attention because:

• Contributor-level accounts are common (guest authors, clients, editors). These accounts may be abused to store persistent payloads.
• Stored XSS is persistent: payloads sit in the database and are served to anyone who loads the affected page, including admins.
• Attackers can escalate via cookie theft, session hijacking, or by injecting further destructive content such as redirects or cryptomining scripts.
• Page builders and custom admin views increase the risk surface: admin screens that render builder content can trigger payloads when editors or admins open them.

Bottom line: treat stored XSS seriously and remediate quickly.

What caused the vulnerability (technical overview)

Stored XSS in page builders typically arises from one or more faults:

• Unsafe output encoding — user-supplied properties (element attributes, custom HTML blocks) are echoed into pages without proper escaping.
• Raw HTML elements allowed for low-trust roles — elements that intentionally permit HTML/JS but aren’t restricted to trusted users.
• Reliance on client-side validation only — no server-side enforcement.
• Insufficient filtering of event handler attributes (onload, onclick), javascript: URIs, or encoded payloads (base64, hex, unicode).

The public advisory suggests a Contributor could insert payloads that were rendered unsanitized to visitors, indicating missing or insufficient output sanitization.

Who is at risk?

• Sites running Bold Page Builder ≤ 5.5.2.
• Sites that allow non-trusted users (Contributors, Authors) to edit content.
• Sites that accept stored submissions (imported content, plugin-stored content) that are later rendered.
• Multisite networks with many low-privilege accounts.

If your WordPress site uses Bold Page Builder, assume risk until you verify otherwise.

Immediate mitigation checklist (next 60–120 minutes)

1. Confirm plugin version:
   • Dashboard → Plugins → Bold Page Builder → check version.
   • Or WP-CLI: wp plugin get bold-page-builder --field=version
2. If version ≤ 5.5.2, plan to update to 5.5.3 immediately. If you cannot update right away (compatibility testing required), proceed with the mitigations below.
3. Restrict editing:
   • Temporarily revoke Contributor/Author editing privileges until patched.
   • Disable or restrict any untrusted accounts that can edit content.
4. Enable WAF / virtual patching:
   • If you have a WAF (hosted or appliance), enable rules to block script tags, event handlers and data/javascript URIs against POSTs that create content.
5. Scan for injected content:
   • Search the database for <script>, inline event handlers, javascript:, and large base64 blobs (see detection section).
6. Harden admin access:
   • Enforce two-factor authentication (2FA) for admin/editor accounts.
   • Rotate passwords for admin, FTP, and hosting panel accounts if compromise is suspected.
7. Take a fresh backup:
   • Export a full site backup (files + database) before making changes so you can revert if needed.

Detection — how to find stored XSS payloads

Stored XSS payloads commonly use markers such as <script>, onerror, onclick, javascript:, or encoded forms. Search your database carefully.

Example SQL searches (backup first, use phpMyAdmin/Adminer/WP-CLI with care):

-- Find script tags in wp_posts.post_content
SELECT ID, post_title
FROM wp_posts
WHERE post_content LIKE '%<script%';

-- Find inline event handlers like onclick, onerror etc.
SELECT ID, post_title
FROM wp_posts
WHERE post_content REGEXP 'on(click|load|error|mouseover|mouseenter)';

-- Search options or plugin tables for script tags
SELECT * FROM wp_options WHERE option_value LIKE '%<script%';

Postmeta and custom builder tables often store JSON or serialized HTML. Example:

SELECT post_id, meta_key, meta_value
FROM wp_postmeta
WHERE meta_value LIKE '%<script%';

Look for encoded payloads (data:application/javascript;base64 or long base64 strings). Search for the token “base64” or unusually long non-space sequences.

When inspecting, prioritise content edited by low-trust users. Some themes/plugins legitimately store inline JS — review context before deleting.

Containment & cleanup (if you find malicious content)

1. Isolate the payload:
   • Edit the affected post/postmeta and remove the malicious markup immediately.
   • If there are many occurrences, consider a controlled bulk cleanup (scripted DOM parsing is safer than naïve string replace).
2. Revoke sessions:
   • Force logout for all users (rotate auth keys or use session invalidation mechanisms).
3. Rotate credentials:
   • Reset passwords for admin/editor accounts, FTP, control panel, and any exposed API keys.
4. Re-scan the site:
   • Run a full-site malware and integrity scan for injected scripts and backdoors.
5. If account compromise is suspected:
   • Audit user accounts and recent edits; remove or lock suspicious accounts.
6. Restore if necessary:
   • If cleanup is complex, restore a clean backup taken prior to the earliest malicious change.

Hardening to prevent similar issues

• Principle of least privilege: restrict Contributor permissions and use content moderation workflows.
• Disable Raw HTML for untrusted roles: only trusted roles should be allowed to insert raw HTML/JS.
• Server-side sanitization: developers must escape output and sanitize inputs using WordPress APIs (wp_kses_post, esc_html, esc_attr).
• Content Security Policy (CSP): a strict CSP can mitigate impact but requires careful tuning.
• Regular updates and staging: test plugin updates on staging before deploying to production.
• Use WAF rules or virtual patching as a temporary mitigation until updates are applied.

Technical mitigations — WAF rules you can deploy immediately

If you cannot update immediately, deploy WAF rules to block common exploitation vectors. Test on staging first to avoid blocking legitimate content.

1) Block literal <script> tags in content POSTs

SecRule REQUEST_BODY "@rx (?i)<\s*script" \
    "id:100001,phase:2,deny,log,msg:'Blocked XSS script tag in request body'"

2) Block javascript: URIs and data URIs in user-submitted URLs

SecRule REQUEST_BODY "@rx (?i)javascript\s*:" \
    "id:100002,phase:2,deny,log,msg:'Blocked javascript: URI in request body'"

SecRule REQUEST_BODY "@rx (?i)data\s*:\s*text/html|data\s*:\s*application/javascript" \
    "id:100003,phase:2,deny,log,msg:'Blocked data: URI in request body'"

3) Block inline event handlers (onload, onclick, onerror, etc.)

SecRule REQUEST_BODY "@rx (?i)on(click|load|error|mouseover|mouseenter|submit)\s*=" \
    "id:100004,phase:2,deny,log,msg:'Blocked inline event handler in request body'"

4) Block encoded <script> tags (hex, unicode, base64)

SecRule REQUEST_BODY "@rx (?i)(%3C|\\u003c).*script|base64\,[A-Za-z0-9+/]{20,}" \
    "id:100005,phase:2,deny,log,msg:'Blocked encoded script or base64 payload'"

Notes:

• Whitelist admin paths cautiously if needed for legitimate admin workflows.
• Log and monitor blocked requests to tune rules and reduce false positives.
• These are conceptual ModSecurity examples; adapt to your WAF engine and test on staging.

How to test if you’re vulnerable (safe testing)

Never test destructive payloads on production. Use staging or local copies. Prefer non-executing probes:

• Insert a harmless marker via a Contributor account and see if it renders. Example: <!--XSS-TEST-12345--> — if the marker appears on the front-end, contributor input reaches rendering paths.
• If scripting tests are necessary, do them on an isolated staging copy. Example payload for staging:

  <img src=x onerror="console.log('XSS TEST')">

Incident response playbook (active exploitation)

1. Put site in maintenance mode to limit exposure to visitors.
2. Snapshot current state and preserve logs (webserver, WAF) for forensics.
3. Remove malicious content from storage but retain forensic copies for analysis.
4. Revoke sessions and rotate credentials.
5. Scan files for backdoors and modified core files; clean or restore from clean backups.
6. Notify impacted users/stakeholders if sensitive data may have been exposed and follow applicable breach reporting rules.
7. Perform root cause analysis and harden systems post-incident.

Example forensic queries and log analysis

• Web server logs: search for POSTs to editor endpoints (e.g., /wp-admin/admin-ajax.php) with suspicious payloads around the disclosure time.
• WAF logs: look for denies matching script tags, event handlers, or base64 sequences.
• Database timeline: check wp_posts.post_date and wp_postmeta for new entries by Contributors around suspicious times.

Long-term remediation for developers (secure coding takeaways)

• Escape on output and sanitize input: use WordPress APIs (esc_html, esc_attr, wp_kses, wp_kses_post).
• Restrict raw HTML to trusted roles only.
• Validate and normalise input server-side.
• Avoid storing untrusted code in settings that render in admin contexts.
• Adopt CSP and automated security tests (SAST) and code reviews focused on output encoding.
• Establish a release process to deliver security patches quickly, and maintain the ability to deploy virtual patches (WAF signatures) temporarily if necessary.

Practical next steps (deploy right now)

• Update Bold Page Builder to 5.5.3 or later immediately where possible.
• If update is not possible:
  • Enable WAF rules to block <script>, inline event handlers, and javascript: URIs.
  • Restrict Contributor/Author editing roles until you patch.
  • Run a content database scan for <script>, base64 payloads, and inline handlers.
  • Force admin logouts and rotate credentials.
  • Apply CSP if feasible and test.
• After patching: re-scan and monitor logs for at least 30 days for suspicious activity.

Example detection signatures

Use these regex/string patterns in scanners or WAF rules (tune to reduce false positives):

• <\s*script\b (script tags)
• on(click|error|load|mouseover|mouseenter|submit)\s*= (inline event handlers)
• javascript\s*: (javascript: URIs)
• data:\s*text/html|data:\s*application/javascript (data URIs)
• base64,[A-Za-z0-9+/]{50,} (large base64 blobs)
• Encoded forms like \\u003c or %3C followed by script

Verification — confirming you’re secure after patching

1. Confirm plugin version is 5.5.3 or later.
2. Re-scan the site for residual script tags or suspicious handlers.
3. Review WAF logs for blocked attempts and unusual volumes of scan/probe traffic.
4. Monitor server access and error logs for unfamiliar IPs or repeated attempts.
5. Perform a post-incident review to confirm root cause and record remediation steps.

Frequently asked questions (FAQ)

Q: I have no Contributors on my site. Am I safe?

A: Having no Contributors reduces the typical attack vector, but payloads may still be introduced via imports, third-party plugins, or compromised accounts. Continue scanning and employ layered controls until patched.

Q: My site is heavily customised and I can’t update immediately. What should I do?

A: Implement WAF/virtual patching immediately, restrict editing roles, scan and clean content, and plan a staged, tested update path using staging environments and backups.

Q: Can CSP 100% stop XSS?

A: No single control is foolproof. CSP is a strong mitigation when correctly configured, but must be paired with output encoding, sanitization, access control, and monitoring.

Final notes — from a Hong Kong security perspective

Page builders are high-value targets because they deal directly with the content layer that many low-privilege users can edit. Stored XSS is dangerous precisely because it persists and can affect site-wide audiences. The recommended approach is layered: patch promptly, restrict the editing surface, scan and remediate stored content, and deploy temporary WAF signatures where necessary. Maintain backups, monitor logs, and conduct a post-incident review if any suspicious activity is found.

If you run Bold Page Builder: prioritise updating to 5.5.3 or later. If immediate updating is not possible, apply the containment and technical mitigations above and scan your site for injected payloads.

Stay vigilant — patch early, monitor continuously, and practise defence in depth.