CVE-2026-4279: The Bread & Butter plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'breadbutter-customevent-button' shortcode in all version...

Description

The Bread & Butter plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'breadbutter-customevent-button' shortcode in all versions up to, and including, 8.2.0.25. This is due to insufficient input sanitization and output escaping on the 'event' shortcode attribute. The customEventShortCodeButton() function takes the 'event' attribute value and directly interpolates it into a JavaScript string within an onclick HTML attribute without applying esc_attr() or esc_js(). Notably, the sister function customEventShortCode() properly uses esc_js() for the same attribute, but this was omitted in the button variant. 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 the page and clicks the injected button.

Metrics

CVSS 3.1

6.4/10

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

EPSS Probability

0.24%

14.3th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-79

References

Timeline

Published: Apr 22, 2026
Last Modified: Jun 17, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2026-4279?

The Bread & Butter plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the 'breadbutter-customevent-button' shortcode in all versions up to, and including, 8.2.0.25. This is due to insufficient input sanitization and output escaping on the 'event' shortcode attribute. The customEventShortCodeButton() function takes the 'event' attribute value and directly interpolates it into a JavaScript string within an onclick HTML attribute without applying esc_attr() or esc_js(). Notably, the sister function customEventShortCode() properly uses esc_js() for the same attribute, but this was omitted in the button variant. 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 the page and clicks the injected button.

How severe is CVE-2026-4279?

CVE-2026-4279 has a CVSS score of 6.4/10 (MEDIUM severity). The EPSS model estimates a 0.24% probability of exploitation in the next 30 days.

How do I fix CVE-2026-4279?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.