# CVE-2026-123139: CVE-2026-123139

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

Improper verification of the source of a communication channel vulnerability in Opera Neon on macOS and Windows allows a malicious browser extension to take control of the browser by sending commands through MCP Hub to the built-in Browser Operator extension. This issue affects Opera Neon MCP Hub extension: 0.0.1.

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Opera / Neon: 1.0.0 (affected, custom). Source: CNA: Opera; platforms: Windows, MacOS

## Severity and prioritization

- CVSS 4.0: 5.8 (medium); CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:L/SI:L/SA:N/E:U; source: CNA: Opera

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-940

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://security.opera.com/en/improper-verification-of-source-of-a-communication-channel-opera-security-advisories/ (CNA: Opera)

## Provenance

- CNA: Opera: https://www.cve.org/CVERecord?id=CVE-2026-123139; retrieved 2026-11-12; source updated 2026-11-12

Revision: cf1e010f2eb379f728fdf8071ee3b548ec772ef005a0655cd5cc446f11bc82ac

Canonical: https://y2.dev/cve/CVE-2026-123139

## 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.