My Calendar decodes encoded fallback attributes into executable script content
My Calendar through 3.8.3 permits a Contributor or higher-privileged user to store hex-escaped script content in the fallback shortcode attribute. The escapes remain literal text during wp_kses_post filtering on save. At rendering, shortcode_parse_atts() calls stripcslashes(), decoding them into HTML before they reach an unescaped output, so scripts run when the page is viewed.
- Component
- My Calendar – Accessible Event Manager
- Plugin slug
my-calendar- Affected
- <= 3.8.3
- Safe version
3.8.4- Published
- Sep 09, 2026
This CVE was published Sep 09, 2026 and is one of 14 known issues for this plugin.
Update, patch or deactivate.
Update My Calendar to 3.8.4 or later. The official changelog identifies the matching fix. The checked current release is 3.8.4.
A safe version is available, so updating to that version or later is the preferred remediation. If an immediate update is not practical, consider a targeted application patch or temporarily restricting the affected functionality.
Deactivate only when warranted by your risk profile, or when advised by your hosting provider in the limited circumstances where the vulnerability cannot otherwise be mitigated. If you’re unsure which action is appropriate, contact Fused or your hosting provider for guidance.
Technical description
The My Calendar – Accessible Event Manager plugin for WordPress is vulnerable to Stored Cross-Site Scripting via 'fallback' Shortcode Attribute in all versions up to, and including, 3.8.3 due to insufficient input sanitization and output escaping. 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. The bypass relies on hex-encoded shortcode attribute payloads (e.g. \x3cscript\x3e), which wp_kses_post cannot strip on save because they appear as literal backslash sequences rather than real HTML tags; WordPress core's shortcode_parse_atts() then calls stripcslashes() at render time, decoding the escapes into real angle brackets before they reach the unescaped sink.
CVE / CNA vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N