Nome do plugin	Intl DateTime Calendar
Type of Vulnerability	Authenticated Stored XSS
CVE Number	CVE-2025-8293
Urgência	Baixo
CVE Publish Date	2025-08-16
Source URL	CVE-2025-8293

Urgent: Intl DateTime Calendar (≤ 1.0.1) Stored XSS (CVE-2025-8293) — What WordPress Site Owners Need to Know and How to Protect Their Sites

Autor: WP-Firewall Security Team
Data: 2025-08-16
Etiquetas: WordPress, Security, WAF, XSS, Plugin Vulnerability, CVE-2025-8293

TL;DR

A stored Cross-Site Scripting (XSS) vulnerability (CVE-2025-8293) affects the WordPress plugin “Intl DateTime Calendar” versions ≤ 1.0.1. An authenticated user with Contributor-level privileges can submit specially crafted input via the plugin’s date parameter that is stored and later rendered without adequate sanitization, leading to a persistent (stored) XSS condition.

This vulnerability has a CVSS-like severity of 6.5 and is exploitable by any authenticated editor-level or lower user who can access the affected input. There is currently no official patch available. If you run this plugin and accept content from Contributor-level users, you should act now: either remove/disable the plugin, mitigate with a web application firewall (WAF) rule or virtual patching, and follow the incident-response guidance below.

In this article we explain what happened, how attackers can abuse this flaw, how to detect if your site is impacted, and practical mitigation and hardening steps — including how a managed WAF (like our WP-Firewall service) can protect your site immediately even before an official plugin update is available.

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Background: What is the vulnerability?

• Affected software: Intl DateTime Calendar plugin for WordPress
• Affected versions: ≤ 1.0.1
• Vulnerability type: Stored (persistent) Cross-Site Scripting (XSS)
• CVE: CVE-2025-8293
• Required privileges: Contributor (authenticated user)
• Published: 16 August 2025

Stored XSS means the malicious payload is saved on the server (for example in a post meta, custom table or other stored content) and served to visitors later. In this case, the plugin accepts a date parameter from authenticated users, stores it, and later outputs it into an admin-facing or public page without proper context-aware escaping/encoding. A stored script will execute in the browser of any user who views the affected page.

Because the attacker needs only Contributor privileges, the bar to exploitation is relatively low on sites that allow user-contributed content (websites with guest blogging, community posts, or collaborative authorship workflows).

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How the attack works (high-level, non-actionable)

1. A user with Contributor privileges submits content that includes a manipulated date field. The plugin persists that value to the database.
2. When the vulnerable page is rendered (either in the admin area, the author preview, or a public page), the stored date value is output without proper escaping.
3. The browser interprets the injected content as executable JavaScript or HTML, running in the context of the site origin.
4. The attacker can use this to perform actions in the victim’s browser, such as stealing session tokens (if cookies are not protected), performing actions on behalf of logged-in users, injecting phishing content, or loading further malware.

Note: I’m intentionally not including proof-of-concept exploit code or payloads. That kind of actionable detail can be misused. Instead, this post focuses on practical detection and defense.

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Why this is important

• Contributor-level access is common: many WordPress sites accept content from non-admin authors. When contributors can inject persistent scripts, the entire site — and all users who view the content — are at risk.
• Stored XSS is often more dangerous than reflected XSS because the payload persists and can affect many visitors or multiple administrative users.
• There is no official fix currently available for the plugin, so site owners must act defensively until the vendor ships a secure release.

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Impact and potential attacker goals

An attacker who successfully exploits stored XSS can:

• Execute arbitrary JavaScript in the context of the victim’s browser.
• Steal session cookies or tokens (if cookies are not set with HttpOnly and appropriate SameSite attributes).
• Perform actions as an authenticated user (e.g., create posts, change content, manipulate settings) if the victim has sufficient privileges.
• Upload additional malicious content or backdoors (if the victim user can perform those actions).
• Phish site administrators by injecting fake admin notices or login prompts.
• Pivot to server-side compromise in some environments (for example, if admin pages are accessed and the attacker can use admin actions triggered by the XSS to upload files).

Even if the attacker cannot immediately escalate to full site takeover, the presence of persistent XSS undermines the trustworthiness of your site, can inject malicious content into analytics and SEO, and may result in penalties from search engines or hosting providers.

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Exploitability assessment

• Required privilege: Contributor. This reduces the barrier to entry — any site that allows contributor submissions or has weak user onboarding might be exposed.
• Remote: Yes, remote (no physical access required).
• Complexity: Moderate (requires identifying and using the plugin interface that accepts the date parameter).
• Prevalence: Depends on plugin usage. If you run Intl DateTime Calendar and accept Contributor content, you are exposed unless you have mitigations in place.

Patch authors assigned this a 6.5 severity score (often representative of a medium/high risk for web apps), reflecting the moderate impact combined with the ease of exploitation on many sites.

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How to quickly determine whether your site is vulnerable or impacted

If you use the Intl DateTime Calendar plugin (≤ 1.0.1) do the following checks:

1. Inventory: Confirm the plugin and version on your site (Dashboard → Plugins). If your plugin is ≤ 1.0.1, treat it as vulnerable.
2. User roles: Check whether non-admin users (Contributor or Author roles) can submit content that might interact with the plugin (posts, calendar events, custom post types).
3. Search for suspicious content:
   • Search post content, custom fields, post meta and comment tables for suspicious <script> tags or inline event attributes like onerror, carregar.
   • Specifically check content produced by Contributors.
4. Audit logs and access logs:
   • Look for unexpected POST requests or parameters containing HTML or unusual characters.
   • Web server logs may include suspicious request lines containing the date parameter with encoded characters.
5. Browser-side indicators:
   • If you find an XSS on a page, viewing it in your browser may trigger unexpected pop-ups, redirects, or injected UI. Do this only in a controlled environment and not while logged in as admin.
6. Malware scanners:
   • Run a server-side scan for injected files and suspicious database entries. A WAF with scanning features will often have signatures for stored XSS patterns.

If you find evidence of malicious content, follow incident response steps below.

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Immediate mitigations (step-by-step)

When there is no official plugin patch available, you should prioritize defensive measures that reduce risk quickly.

1. Disable the plugin (recommended)
   The simplest and most reliable mitigation is to deactivate or remove the vulnerable plugin until an update is provided. If the plugin is not essential to your site’s operation, uninstall it.
2. Restrict Contributor access
   Temporarily restrict or disable Contributor-level user creation or submission workflows until the plugin is patched.
   Change contributor workflows: require admin approval of all posts, block untrusted users from uploading content or adding HTML.
3. Harden user roles and capabilities
   Review all user accounts. Remove or disable stale or unused accounts.
   Promote strict moderation: every user-generated submission should pass through a reviewer.
4. Apply virtual patching with WAF rules
   If you run a web application firewall (WAF), apply an input-blocking rule that blocks or sanitizes requests where the date parameter contains HTML/script tokens or encoded equivalents.
   A managed firewall (such as WP-Firewall) can deploy rules quickly without waiting for the plugin author to ship a patch.
5. Content Security Policy (CSP) and cookie protection
   Implement a restrictive CSP to limit inline script execution and external script loading.
   Ensure cookies use HttpOnly and SameSite attributes; set the session cookie to be Secure (HTTPS) and HttpOnly to limit cookie theft via XSS.
6. Cleanup and verification
   Inspect database records for posts, post_meta, comments, or custom tables for stored payloads. Remove or sanitize suspicious content.
   Re-scan the site for server-side backdoors or modified core/plugin/theme files.
7. Monitoring and logging
   Increase monitoring of logs for suspicious POSTs, unusual admin page access, and high error rates.
   Configure alerts for new user registrations, role changes, and new published posts from non-admin users.

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How a managed WAF like WP-Firewall mitigates this vulnerability immediately

Managed WAFs provide an effective interim layer of defense while you wait for official fixes. Here’s how we handle a scenario like this:

• Rapid virtual patching: We create and deploy a rule that intercepts requests looking like exploit attempts (for example, any request with a date parameter that contains script tags or common XSS payload patterns) and either blocks or sanitizes the input before it reaches WordPress.
• Context-aware blocking: Rather than blocking all requests using the word “date”, our rules target unusual or malicious encodings, HTML tags, event handlers, and base64-encoded payloads delivered in parameters or request bodies.
• Granular adaptation: Rules can be scoped to the affected plugin’s endpoints (so you don’t interfere with other site functionality).
• Response modification: When stored payloads already exist in content, the WAF can serve a sanitized copy to visitors or strip dangerous tags from content at render time.
• Monitoring and alerting: WAF logs indicate attempted exploit patterns so you can triage and investigate suspicious users and submissions.

Note: A WAF is not a permanent substitute for code fixes, but it’s a realistic and immediate protection method while you coordinate with plugin authors and security teams for a proper patch.

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Example of defensive WAF rule (pseudo-code)

Rule: Block HTML/script injection in "date" parameter
Trigger:
  - HTTP_METHOD in (POST, PUT)
  - Request contains parameter "date"
Condition:
  - The value of "date" after URL-decode matches regex:
    (?i).*<(?:script|iframe|img|svg|math|video|audio|body|object|embed|link)[\s>].*
    OR contains "onerror"|"onload"|"javascript:"|"data:text/html"
Action:
  - Block request with HTTP 403
  - Log full request detail (header + body) to WAF audit log
  - (Optional) Send email alert to site admin

Important: tune the regex and logic to avoid false positives (e.g., some legitimate date formats may include < or other characters when malformed or encoded). Use logging-only mode first to understand impact.

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Safer content rendering & hardening tips (developer guidance)

If you maintain custom themes or plugin code, adopt these best practices immediately:

• Contextual escaping: Use the correct escaping functions when rendering data:
  • For HTML body content use wp_kses() with a strict allowed list.
  • For attributes use esc_attr().
  • For JavaScript contexts, use wp_json_encode() where appropriate to safely insert server-side data into script blocks.
• Sanitize on input and escape on output: Do not rely solely on input validation. Store raw data only when you have robust escaping at output time.
• Avoid echoing user-submitted values directly into admin-facing pages without sanitization.
• Use nonces and capability checks for any actions that modify content, even if coming from authenticated users.
• Implement strict allowed HTML lists for contributor-submitted content. For example, use wp_kses_post() as a baseline and further restrict tags for non-trusted roles.

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Incident response checklist (if you suspect compromise)

If you discover that an XSS payload was successfully injected and potentially executed, follow a thorough incident-response procedure:

1. Isolate: Temporarily disable the vulnerable plugin or take the site into maintenance mode to block further exposures.
2. Preserve forensic data: Export logs (WAF, webserver, application) and take file and database snapshots for analysis.
3. Rotate credentials:
   • Force password resets for all administrator accounts.
   • Revoke and reissue any API keys, tokens, or integration credentials that may have been exposed.
   • Invalidate active sessions where possible.
4. Clean up the injected content:
   • Remove malicious stored payloads in posts, metadata, comments, and plugin data tables.
   • Search for and remove any uploaded backdoors or modified PHP files.
5. Re-scan the environment: Run a full malware and integrity scan on files and database.
6. Rebuild if necessary: If the site appears to have been significantly modified, prefer a rebuild from known-good backups rather than attempt to scrub a compromised install.
7. Document and report: Keep records of the incident and, if required, report to your hosting provider and upstream stakeholders.
8. Re-enable protections: Before bringing the site back online, ensure mitigations (WAF rules, CSP, patched plugin, etc.) are in place.

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Long-term hardening to prevent similar problems

• Principle of least privilege:
  • Limit the Contributor role’s abilities: no unmoderated publishing and no file upload if not necessary.
  • Require admin approval for any user-submitted HTML or rich content.
• Plugin governance:
  • Only install plugins from trusted sources; keep inventory and update regularly.
  • Deactivate and remove plugins that are unused or poorly maintained.
• Harden cookies and headers:
  • Set Secure, HttpOnly, and SameSite attributes for cookies.
  • Employ a Content Security Policy that restricts sources of executable scripts.
  • Use X-Content-Type-Options: nosniff and X-Frame-Options: SAMEORIGIN.
• Continuous monitoring:
  • File integrity monitoring (FIM) to detect unexpected changes.
  • Log aggregation with alerts for suspicious POSTs, unusual admin logins, and privilege escalations.
• Regular security reviews:
  • Periodic manual review of user accounts and content moderation queues.
  • Pen tests and vulnerability scans that include plugin assessments.

Example CSP snippet (set cautiously and test):

Content-Security-Policy:
  default-src 'self';
  script-src 'self' 'nonce-<random>' https://trusted.cdn.example;
  object-src 'none';
  frame-ancestors 'none';

This helps reduce the blast radius of XSS by limiting where scripts may load from and by using nonces for any inline scripts you intentionally allow.

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Detection: what to look for in logs and audits

• POST requests to plugin endpoints with unusually long date parameter values or containing encoded sequences like %3C (URL-encoded <).
• Non-admin users performing multiple rapid submissions or attempting to publish content containing HTML tags.
• Unexpected changes to published posts shortly after contributor submissions.
• WAF logs showing repeated rule hits from the same accounts or IP addresses against the date parâmetro.
• Browser-based reports of popups, redirects, or strange page behavior from moderators or administrators viewing content.

If you enable WAF logging or set rules to log-only for a short period before blocking, you’ll gather valuable intel about attempted exploitation and which accounts might be involved.

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Why virtual patching matters now

When a plugin author has not yet released a fix, you still need to protect your site. Virtual patching (temporary rule-based mitigation at the WAF level) prevents malicious requests from reaching the vulnerable code path, buys time for a vendor patch and coordinated disclosure follow-up, and reduces immediate risk to site visitors and administrators.

At WP-Firewall we deploy virtual patches rapidly and monitor for bypass attempts, ensuring the mitigation is tuned and does not disrupt legitimate site behavior.

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Practical examples of what NOT to do

• Don’t ignore the vulnerability because it requires Contributor access. Many sites allow contributor registration or third-party authorships.
• Don’t assume only public-facing pages are affected — admin or preview pages can also execute stored payloads if an admin views the malicious content.
• Don’t rely solely on client-side defenses (like browser extensions) — defense-in-depth is required: server-side sanitation, escaping, WAF rules, CSP and secure cookies are all needed.

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Communications and responsible disclosure

If you maintain a site impacted by this vulnerability:

• Notify your internal stakeholders, hosting provider and any affected third parties if you suspect a compromise.
• Encourage contributors to re-submit content only after administrative review.
• Track updates from the plugin maintainer and the CVE database for an official patch release.

If you are a developer or plugin author, prioritize a security fix: properly escape output, add input validation, and publish an update with full release notes and recommended upgrade instructions.

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Closing thoughts

Stored XSS vulnerabilities like CVE-2025-8293 are a stark reminder that even low/medium severity issues can create serious operational risk—especially on community-driven sites that accept content from authenticated users. The fastest way to reduce risk is to disable or remove the vulnerable plugin if you can, or apply virtual patching via a managed WAF while you await an official update. Complement these steps with a solid hygiene routine: least privilege, content moderation, CSP, and strong cookie settings.

If you’d like help assessing your exposure or applying rapid protections for your sites, our security team can assist with virtual patching, rule tuning, and incident response guidance. Remember: it’s better to mitigate now than to respond to a visible incident later.

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