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Cross-site Scripting (XSS)Weakness · CWE-79

CVE-2026-8899

MEDIUM · 6.4 CVSS v3.1 Published 2026-05-27
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
The Auto Thumbnail plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'thumbnails' shortcode in all versions up to, and including, 1.0. This is due to insufficient input sanitization and output escaping on the shortcode's 'width' and 'height' attributes in the athn_thumbnails() function, which are concatenated directly into an HTML <img> tag. 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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The Auto Thumbnail WordPress plugin (versions up to 1.0) contains a stored XSS vulnerability in the athn_thumbnails() function. The 'width' and 'height' attributes from the thumbnails shortcode are not sanitized before being directly concatenated into an HTML <img> tag, allowing authenticated contributors+ to inject arbitrary JavaScript.

MitigationSanitize and escape the width and height attributes using appropriate functions (e.g., absint() or intval for integers, plus esc_attr()) before outputting in the HTML tag. Update plugin if patched version available.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Auto Thumbnail plugin is installed
    Go to WordPress admin > Plugins and look for 'Auto Thumbnail' in the installed plugins list, or check the plugin header file for version information in wp-content/plugins/auto-thumbnail/ or similar path
    Affected if plugin is not installed or not present in the site
  2. Verify plugin version is 1.0 or lower
    Check the main plugin file (usually auto-thumbnail.php) for the 'Version' header comment, or view the plugin details in WP admin plugins list
    Affected if version displayed is 1.0 or lower (or no version number is shown, indicating very early release)
  3. Identify if shortcode is in use
    Search post content, page content, or widget text for the thumbnail shortcode (commonly [athumbnail] or similar pattern using athn_thumbnails function), or check theme files for do_shortcode calls
    Affected if shortcode with width or height attributes is present in any published content
  4. Inspect the vulnerable code path
    Locate the athn_thumbnails function in the plugin file and examine how $width and $height variables are handled before HTML output - look for direct concatenation into img tags without sanitization functions like esc_attr(), absint(), or intval()
    Affected if code shows width/height values are output directly without sanitization using absint(), intval(), or esc_attr()
  5. Check for contributor+ user accounts
    Review WordPress users in admin > Users section and identify any accounts with Contributor, Author, Editor, or Administrator roles
    Affected if any user account with Contributor-level access or higher exists on the site

You are affected if the Auto Thumbnail plugin (version 1.0 or lower) is installed, the thumbnail shortcode with width/height attributes is in use on your site, and your plugin code lacks proper sanitization - combined with any contributor+ user account that could potentially inject the malicious payload.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Sanitize and escape the width and height attributes using appropriate functions (e.g., absint() or intval for integers, plus esc_attr()) before outputting in the HTML tag. Update plugin if patched version available.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,060
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-8899 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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