플러그인 이름	Mosaic Generator
Type of Vulnerability	저장된 XSS
CVE Number	CVE-2025-8621
긴급	낮은
CVE Publish Date	2025-08-11
Source URL	CVE-2025-8621

Urgent Alert: Mosaic Generator (≤ 1.0.5) — Authenticated (Contributor+) Stored XSS via c Parameter (CVE‑2025‑8621)

게시됨: 11 August 2025
작가: WP‑Firewall Security Team — WordPress Security & WAF Specialists

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요약

A stored Cross‑Site Scripting (XSS) vulnerability has been reported in the Mosaic Generator WordPress plugin, affecting versions ≤ 1.0.5. Authenticated users with Contributor (or higher) privileges can inject content via the c parameter that is persisted and later rendered in pages viewed by other users or administrators. There is no official patch available at the time of this alert. This advisory explains the risk, realistic attack scenarios, safe detection methods, and both immediate and long‑term mitigations — including how a WAF and virtual patching can protect your site while an official fix is produced.

Note: If your site allows contributor+ accounts (Contributor, Author, Editor, Administrator) and you use Mosaic Generator, treat this as high priority for review despite an overall CVSS classification that places the issue in the mid range. Stored XSS that can be injected by authenticated users is often used as a stepping stone to full site compromise.

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What is the issue?

• Vulnerability type: Stored Cross‑Site Scripting (XSS), OWASP A7 (XSS).
• Affected software: Mosaic Generator WordPress plugin
• Affected versions: ≤ 1.0.5
• Required privileges to exploit: Contributor or higher (authenticated)
• CVE: CVE‑2025‑8621
• Public disclosure: 11 August 2025
• Official patch status: No official fix available (N/A)

In short: the plugin accepts and stores input provided through a parameter named c without proper sanitization and/or output encoding. When the stored content is later rendered in the frontend or admin pages, the unsanitized payload executes in the context of a victim’s browser.

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Why this matters — realistic attack vectors

Stored XSS is more dangerous than reflected XSS because the payload is persisted in the site database and can trigger every time a page containing that content is viewed. When an authenticated contributor can persist HTML/JS that’s later displayed to editors or site visitors, multiple attack chains are possible:

• Stealing admin session cookies or authentication tokens if cookies are not properly protected (HttpOnly, SameSite).
• Performing actions on behalf of an administrative user (CSRF combined with XSS) to install malicious plugins/themes, create new administrator accounts, or alter site configuration.
• Delivering secondary payloads: redirect visitors to malicious sites, show phishing forms, or force downloads to plant backdoors.
• Bypassing content moderation processes by hiding payloads in encoded forms and revealing them at render time.
• Targeting editors and administrators to escalate privileges and gain persistent access.

Even when the initial attacker is only a Contributor (a typical role for guest writers or external collaborators), they can weaponize stored XSS to take over accounts with higher privileges.

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Attack scenarios (illustrative, not exploit code)

1. Contributor injects a malicious JavaScript snippet into a mosaic or description field via the c parameter when creating or editing content. The payload is stored in the plugin’s data tables.
2. An Editor or Administrator opens the mosaic preview page or the plugin management page in the admin dashboard; the stored payload executes in their browser.
3. Using XSS, the attacker sends a request to an administration endpoint (for example, create a new user or update plugin files) that relies on the admin’s logged‑in session. If successful, the attacker escalates access or establishes a backdoor.
4. The attacker hides persistence by creating a new admin user with an innocuous username or injects a scheduled task (cron) that maintains access.

Because of the persistence and the potential to target higher privilege users, site owners must treat stored XSS vulnerabilities seriously.

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Detection — how to check if you’re impacted

1. Inventory
   • Confirm whether your site runs the Mosaic Generator plugin and which version (Dashboard → Plugins or WP‑CLI wp plugin list).
   • If your version is ≤ 1.0.5 and you have users with Contributor or higher roles, consider the site impacted until mitigations are in place.
2. Search for suspicious stored content
   • Look for unusual <script> tags, HTML event attributes (e.g., onerror=, onclick=), javascript: URIs, or encoded payloads in posts, postmeta, and plugin tables.
   • Example (safe) SQL queries you can run from your DB management tool to find indicators — these look for obvious script tags; adapt them and use caution when running queries on production:
     • Search post content:
       SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%<script%' OR post_content LIKE '%onerror=%' OR post_content LIKE '%javascript:%';
     • Search post meta (plugin data often stored here):
       SELECT post_id, meta_key, meta_value FROM wp_postmeta WHERE meta_value LIKE '%<script%' OR meta_value LIKE '%onerror=%' OR meta_value LIKE '%javascript:%';
     • Search options table:
       SELECT option_name FROM wp_options WHERE option_value LIKE '%<script%' OR option_value LIKE '%onerror=%';
   • Use WP‑CLI if you prefer:
     wp db query "SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%<script%';"
   • Note: Attackers might obfuscate payloads. Also search for suspicious base64 strings or long HTML entities.
3. Log review
   • Check web server logs for requests that include the c parameter with unusual characters around the time user accounts edited or created content.
   • Look at access logs for POST/GET requests with c= from authenticated user IPs.
4. User account review
   • Audit accounts with Contributor and higher roles. Look for accounts created recently or accounts that were used at times that correlate with suspicious content insertion.
5. Malware scanning
   • Run a backend malware scan (filesystem and database). Look for new files, modified plugin/theme files, and webshells.

If you find evidence of exploitation (unexpected script tags, newly created administrator accounts, or unknown scheduled tasks), treat this as an incident — see the Incident Response section below.

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Immediate mitigations (what to do now)

If you cannot immediately remove or update the plugin, apply an emergency mitigation plan:

1. Reduce exposure
   • Disable or deactivate the Mosaic Generator plugin until an official patch is available and you have verified a safe upgrade path.
     wp plugin deactivate mosaic-generator
   • If the plugin is needed, restrict who can use it: temporarily remove Contributor and lower access to the plugin features, or change roles so only trusted Editors/Administrators can create mosaics.
2. Harden user permissions
   • Review contributor accounts. Remove or suspend suspicious contributors.
   • Require stronger vetting and monitoring of external authors.
   • Consider converting untrusted Contributor accounts to lower‑privilege roles (Subscriber) until the issue is resolved.
3. Content sanitization / remove known payloads
   • Search the database for probable payloads (see Detection section) and remove or sanitize offending entries.
   • Export suspected posts and review them carefully before re‑publishing.
   • If you restore from a backup, ensure the backup predates any possible injection and that it is clean.
4. Apply WAF / Virtual patching (recommended while waiting for official fix)
   • Deploy a Web Application Firewall rule to block requests containing suspicious c parameter values or to block requests that attempt to write HTML tags or script content.
   • Implement rules to block or sanitize the c parameter content if it contains <, >, script, or event handlers.
   • Monitor and block attempts to access the plugin admin endpoints from non‑trusted IPs.
5. Protect session cookies and admin access
   • Ensure cookies use HttpOnly and SameSite flags; use secure cookies (HTTPS).
   • Remove persistent login cookies for admin/editor accounts and require fresh authentication.
   • Enforce 2‑factor authentication (2FA) for admin and editor accounts.
6. Scan and review server configuration
   • Temporarily increase logging level to capture exploit attempts.
   • Check file system for modified plugin or theme files and unknown PHP files.

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Why a WAF or virtual patch helps (how we would protect you)

A well‑configured WordPress Web Application Firewall (WAF) provides virtual patching: it mitigates the vulnerability at the request/response boundary without modifying plugin code. This is crucial when an official patch is unavailable.

Key WAF strategies for this case:

• Block requests that include dangerous payloads in the c parameter (server‑side inspection). For example, block requests where c contains <script or encoded variants.
• Block requests that attempt to submit HTML/JS to plugin endpoints (POST requests to plugin admin or AJAX endpoints).
• Filter outgoing HTML to strip known patterns that would execute as JavaScript (when practical and safe).
• Implement rate limits and anomaly detection on user accounts to detect automation or repeated attempts.

Note: virtual patching must be implemented carefully to avoid false positives that break legitimate functionality. The best approach is tuned and monitored rules that are updated as more intelligence becomes available.

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Long‑term remediation (for developers and site maintainers)

If you maintain a site development team or you are the plugin author, take these code‑level steps to fix the underlying cause:

1. Proper input validation and sanitization
   • On input, perform strict validation for the expected data type and format. If a parameter should be an ID, number, or limited string, reject anything else.
   • Avoid allowing raw HTML input unless explicitly required. Where HTML is required, use a safe HTML sanitizer (e.g., allowed HTML via wp_kses with a strict whitelist).
2. Output escaping
   • Always escape output based on context (esc_html(), esc_attr(), esc_js(), wp_kses_post, etc.). Even if data is sanitized on input, escape on output as a second layer.
3. Capability checks and nonce validation
   • Ensure that any endpoint processing the c parameter validates the current user’s capabilities.
   • Add and verify nonces for actions that modify or store data — this helps protect against CSRF chains combined with XSS.
4. Store data safely
   • If storing generated markup or user input, consider storing a sanitized form and a separate raw form only where strictly necessary, with access restrictions.
   • Avoid injecting user content directly into admin pages or JavaScript contexts.
5. Security reviews and automated testing
   • Add automated tests to check that input is sanitized and output escaped.
   • Include security checks in your CI/CD pipeline where applicable.

If you’re a plugin developer: when you release a patch, also publish a disclosure advising administrators about the upgrade path and recommended emergency mitigations, and provide guidance for administrators who may already be compromised.

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Incident response checklist (if you suspect exploitation)

If you find evidence of exploitation, take the following steps immediately:

1. Isolate and contain
   • Deactivate the vulnerable plugin.
   • Limit admin/editor access and force password resets for high‑privilege accounts.
   • Temporarily disable any unknown plugins/themes.
2. Preserve evidence
   • Export logs, database snapshots, and copies of affected files for forensic review.
   • Do not perform destructive cleanup before preserving evidence.
3. Clean and recover
   • Remove any malicious scripts from the database or files.
   • Restore from a clean backup if available and if you can ensure the backup is not infected.
   • Rotate all administrator passwords and any API keys stored on the site.
4. Post‑compromise hardening
   • Apply the long‑term remediations above.
   • Rebuild compromised accounts or recreate new admin accounts only after confirming a clean environment.
5. Get professional help if needed
   • If you detect persistence, unknown scheduled tasks, or backdoors you cannot remove, enlist a professional incident response service to perform a full remediation.

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Safe detection scripts and admin checks (practical, non‑exploit, read‑only)

Here are practical checks you can run. These do not contain exploit payloads and are safe to execute. Always test on staging or run in read‑only mode on production.

• WP‑CLI: list plugin version
  wp plugin list --format=csv | grep -i mosaic
• WP‑CLI: search posts for script-like content
  wp db query "SELECT ID, post_title FROM wp_posts WHERE post_content LIKE '%<script%' OR post_content LIKE '%onerror=%' LIMIT 100;"
• MySQL: find suspicious postmeta entries (example)
  SELECT post_id, meta_key FROM wp_postmeta WHERE meta_value LIKE '%<script%' OR meta_value LIKE '%onerror=%' LIMIT 200;
• File system check: find recently modified PHP files in wp-content
  find wp-content -type f -mtime -14 -name '*.php' -print
• List recently created users
  SELECT ID, user_login, user_email, user_registered FROM wp_users WHERE user_registered > DATE_SUB(NOW(), INTERVAL 30 DAY);

These queries are starting points and need to be adapted to your environment (different table prefixes, etc.). Do not edit results in place without backup.

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How WP‑Firewall helps (virtual patching, detection & mitigation)

As a WordPress firewall and security service provider, our recommended layered approach includes:

• Managed WAF rules that specifically target this class of stored XSS — inspecting both GET and POST parameters and blocking attempts to submit scripts or HTML to plugin endpoints.
• Virtual patching (vPatching) that prevents known exploit vectors from reaching the application while you wait for a code patch.
• Real‑time rule updates driven by threat intelligence so protection is activated quickly when disclosures occur.
• Malware scanning that includes database scanning for stored payloads and filesystem scanning for newly added webshells.
• Guided incident response playbooks to help you contain and clean up if exploitation occurred.

If you run WP‑Firewall, we will deploy tuned virtual patches for the Mosaic Generator vulnerability to block exploit attempts at the edge and reduce the risk to your site immediately.

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Frequently asked questions

Q: If I am only using Contributors and I trust them, am I still at risk?
A: Yes. Trusted contributors can still make mistakes or accounts can be compromised. If contributors are allowed to input HTML or use plugin interfaces that accept parameters, there’s an attack surface. Limit the ability to paste raw HTML and require moderation.

Q: Does disabling mosaics remove the risk?
A: Deactivating the plugin prevents new injections, but stored payloads in the database may remain and execute if other parts of the site render that data. You must also search and sanitize stored content before re‑enabling.

Q: Should I remove the plugin entirely?
A: If you cannot immediately verify a safe version or apply virtual patches, deactivating and removing the plugin is the safest choice. Reinstall and reconfigure only after confirming a patched version is available.

Q: Can Content Security Policy (CSP) fully prevent exploit?
A: CSP can reduce impact by blocking inline scripts and external resource loads, but it requires careful configuration and may break existing functionality. CSP is one layer — use it together with input validation, escaping, and a WAF.

Q: What about backups?
A: Backups are essential, but infected backups will reintroduce the problem. Always validate backups for cleanliness before restoring.

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Recommended immediate checklist (summary)

• Confirm plugin version. If ≤ 1.0.5, assume the site is vulnerable.
• Deactivate the plugin or restrict access to plugin features.
• Audit Contributor+ accounts; suspend suspicious accounts.
• Review database for stored <script> tags and event handlers; sanitize or remove entries.
• Deploy WAF/virtual patching to block payloads targeting the c parameter and plugin endpoints.
• Harden admin sessions (HttpOnly, SameSite, 2FA), rotate passwords.
• Preserve logs and evidence if you suspect compromise; consider professional incident response for persistent infections.

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Final notes from WP‑Firewall Security Team

Stored XSS vulnerabilities that require only Contributor privileges are very practical for attackers and should not be underestimated. Even when a CVSS value suggests medium severity, the real world impact depends on site configuration, which users view the affected content, and the presence (or absence) of compensating controls like WAFs and content sanitizers.

Take decisive action: inventory, isolate, and harden. Use virtual patching to stop exploitation immediately while you sanitize stored content or wait for an official plugin upgrade. If you need assistance with rule tuning, incident response, or rapid virtual patching, WP‑Firewall specialists are available to help you secure your site quickly and with minimal downtime.

Stay safe, and prioritize protecting administrator and editor accounts — they are the prime targets for chained attacks that lead to full site compromise.

— WP‑Firewall Security Team