JavaScript Injection Vulnerability in Custom Block Builder Plugin for WordPress
CVE-2026-8981

3.5LOW

Key Information:

Vendor

WordPress
Status
Custom Block Builder
Vendor
CVE Published:
9 June 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-8981?

The Custom Block Builder plugin for WordPress prior to version 4.3.0 fails to correctly validate the unfiltered_html capability for all paths writing to block template code fields. This oversight permits administrators on multisite setups, or on single-site installations with DISALLOW_UNFILTERED_HTML defined, to inject malicious JavaScript. Such scripts execute for any visitor viewing pages that incorporate the compromised block, thereby posing a serious security risk.

Affected Version(s)

Custom Block Builder 0 < 4.3.0

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-8981 - Proof of Concept

References

https://wpscan.com/vulnerability/9815b0e6-e411-4a5c-9c63-...
exploitvdb-entrytechnical-description

CVSS V3.1

Score:
3.5
Severity:
LOW
Confidentiality:
Low
Integrity:
Low
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
High
User Interaction:
Required
Scope:
Unchanged

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

Luca Jungnickel
WPScan
.