Lazy Blocks < 4.3.0 - Admin+ Stored XSS via Custom Block Frontend HTML
Priority LOW 16CWE-79Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- High
- User interaction
- Required
- Attack complexity
- Low
- Impact type
- Cross-site scripting
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA. Impact type from CWE-79.
Summary
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.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00138 3rd percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by the CNA
Fix Fixed Custom Block Builder (Unknown): 4.3.0
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Unknown | Custom Block Builder | before 4.3.0 | 4.3.0 | Patch available | CNA |
- Custom Block Builder VendorUnknown Affected before 4.3.0 Fixed in 4.3.0 Patch available CNA
Remediation
- Fix · CNA Custom Block Builder (Unknown) Fixed in 4.3.0
Timeline
- 2026-10-02 Threatist record created from CVE-2026-8981
- 2026-10-03 Alias added: GHSA-cfcv-65jq-76jw
References
Sources
- CVE-2026-8981 · CVE Program
- CVE-2026-8981 · NVD
- FIRST EPSS
- GHSA-cfcv-65jq-76jw · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences