Custom Block Builder: A security weakness
Custom Block Builder is affected by a security weakness. Exposure depends on how the affected operation is made reachable by the site. The resulting impact depends on how the affected component exposes the vulnerable operation. The published affected range is < 4.3.0.
- Component
- Custom Block Builder
- Plugin slug
custom-block-builder- Affected
- < 4.3.0
- Safe version
4.3.0- Published
- Jun 09, 2026
This CVE was published Jun 09, 2026 and is one of 1 known issue for this plugin.
Update, patch or deactivate.
Update Custom Block Builder to 4.3.0 or later, or disable and remove it until a fixed version is available.
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 Custom Block Builder WordPress plugin before 4.3.0 does not consistently check the unfiltered_html capability across all paths that write to its block template code fields, allowing administrators on multisite installations (or single-site installs with DISALLOW_UNFILTERED_HTML defined) to inject arbitrary JavaScript that executes for any visitor of pages embedding the affected block.
CVE / CNA vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:L/I:L/A:N