Ultimate Post WordPress Plugin Stored Cross-Site Scripting Vulnerability
The Ultimate Post plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'moreResultsText' block attribute of the ultimate-post/advanced-search block in versions up to and including 5.0.31. This is due to insufficient input sanitization and output escaping in the Advanced_Search::content() render callback: the attribute value is filtered with wp_kses(), which strips disallowed HTML tags but does NOT escape HTML special characters such as double quotes in plain text, and the result is then concatenated directly into the data-viewmoretext HTML attribute without esc_attr(). This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.
Browse WordPress security risksQuick answer
Ultimate Post should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- Ultimate Post up to and including 5.0.31
Fixed versions
- Apply the latest vendor-supported patched version.
How to fix it
Ultimate Post is affected by CVE-2026-13253. Vulnerable versions up to 5.0.31 allow stored cross-site scripting: contributor-level users can inject stored script through the moreResultsText block attribute. Patch or disable the plugin, then clean stored content and review administrator sessions.
- Inventory all WordPress sites using Ultimate Post.
- Update Ultimate Post beyond 5.0.31 when a vendor-fixed release is available.
- Disable the plugin temporarily if patching is delayed and the affected workflow is reachable.
- Review shortcode attributes, form submissions, merge fields, blocks, and plugin records for stored script payloads.
- Remove malicious content and purge WordPress, object, page, and CDN caches.
- Apply a Content Security Policy where compatible to reduce XSS impact.
- Review administrator sessions and reset credentials if privileged users interacted with injected content.
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Verify the fix
- Confirm Ultimate Post is no longer running version 5.0.31 or older.
- Submit harmless script-like input in staging and confirm it is rejected or escaped on output.
- Open affected pages or admin lookup flows and confirm no stored script executes.
- Review rendered HTML for unsafe unescaped plugin attributes.
- Run a Fixnx scan and verify public WordPress exposure after cleanup.
Related categories
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Trusted references
FAQ
What is affected by CVE-2026-13253?
Ultimate Post versions listed as affected should be reviewed: Ultimate Post up to and including 5.0.31.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.