Opera Neon: an installed extension can drive the browser agent

01What happened

Opera published advisory CVE-2026-123139 on November 12, 2026 for Opera Neon on macOS and Windows, naming improper verification of the source of a communication channel in the Opera Neon MCP Hub extension, version 0.0.1. Opera is the assigning CNA and the record reached the GitHub Advisory Database the same day. No outside researcher is credited on either page.

02How it works

Opera Neon ships MCP Hub, which lets Model Context Protocol clients act inside the live browser session, and a built-in Browser Operator extension that carries those actions out. MCP Hub does not verify which extension a command came from, the weakness GitHub classifies as CWE-940. A malicious browser extension running in the same browser can therefore push commands through the hub to Browser Operator, and whatever controls Browser Operator controls the browsing session.

03Who is affected

Users of Opera Neon on macOS and Windows running MCP Hub extension version 0.0.1 are in scope. Exploitation needs a hostile extension already installed in the same browser, so somebody who installs only extensions they trust is not exposed by this flaw on its own.

04What to do

Review the extensions installed in Opera Neon and remove any that are unfamiliar or no longer needed. Opera's advisory names no fixed version, so take Opera Neon updates as they ship and treat MCP Hub as reachable by anything running with extension privileges.

Questions people ask

Can a website exploit the Opera Neon MCP Hub flaw on its own?

No. Opera's advisory describes the attacker as a malicious browser extension, and the CVSS v4 vector published with the record uses a local attack vector with passive user interaction. A page visited in Opera Neon cannot reach MCP Hub this way. The practical precondition is that a hostile extension is already installed and running in the same browser.

Is there a patched version of Opera Neon for CVE-2026-123139?

Opera's advisory does not state a fixed version, and the GitHub Advisory Database entry lists the patched version as unknown. The only component version named anywhere is the affected one, Opera Neon MCP Hub extension 0.0.1. Until Opera names a fix, the practical step is to keep Opera Neon updated and to audit which extensions are installed.

What is Browser Operator in Opera Neon, and why does it matter here?

Browser Operator is the built-in Opera Neon extension that performs actions inside the user's live browsing session on behalf of an AI client. MCP Hub is the channel that carries those commands to it. Because the hub does not check which extension sent a command, Browser Operator will act on instructions from an attacker's extension as readily as on legitimate ones.

Sources 2 links, all fetched

1. 1security.opera.comOpera Advisory
2. 2github.comGitHub Advisory