# CVE-2026-121491: Fiber Admin 3.1.0 - 4.0.0 - Unauthenticated RCE via Host Header

Status: published. Published: 2026-11-07. Updated: 2026-11-07.

The Fiber Admin WordPress plugin before 4.0.1 does not validate or escape a request header before writing it into a PHP file it regenerates on an unprotected admin hook, allowing unauthenticated attackers to execute arbitrary code when its custom database error page is enabled and they win a race against an administrator saving its settings.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Unknown / Fiber Admin: ≥ 3.1.0; < 4.0.1 (affected, semver). Source: CNA: WPScan

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-94

## Exploit evidence

- exploit: https://wpscan.com/vulnerability/42b9773d-9c69-4435-be20-ae86f52b4608/ (CNA: WPScan)

## References

- https://wpscan.com/vulnerability/42b9773d-9c69-4435-be20-ae86f52b4608/ (CNA: WPScan; exploit, vdb-entry, technical-description)

## Provenance

- CNA: WPScan: https://www.cve.org/CVERecord?id=CVE-2026-121491; retrieved 2026-11-07; source updated 2026-11-07

Revision: 34f187a3f25e914ec571f42d8ec52d67b6db8ce50a9d4ac92ee1ed0d7943e680

Canonical: https://y2.dev/cve/CVE-2026-121491

## Agent and API access

Public CVE pages, Markdown, and JSON are free to read without an account or API key.

- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

- WebMCP: search_cve_disclosures, get_cve_disclosure, get_cve_page_markdown, get_y2_cve_access. Available in compatible browsers.

- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.