# CVE-2026-123139: Code injection in Neon

> A malicious browser extension can take control of the browser via MCP Hub commands to Opera Neon's Browser Operator extension.

- **Severity:** Medium 5.8 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Harmful if only installed:** No
- **Needs a specific call:** No
- **Fix available:** No
- **Published:** 12 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-2f45-6797-cj93

## What is CVE-2026-123139?

CVE-2026-123139 is a medium-severity code injection vulnerability in Opera Neon, published on 12 Nov 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

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.

Weakness: CWE-940 (Improper Verification of Source of a Communication Channel)

## Which versions are affected by CVE-2026-123139?

An affected version is exposed as installed. No special setting or call is needed.


## How do I fix CVE-2026-123139?

No fix has been published for CVE-2026-123139 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-123139 being exploited?

There is no known exploitation of CVE-2026-123139 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-123139 and fix it if it is affected.

What it is: CVE-2026-123139 is a medium-severity code injection vulnerability in Opera Neon, published on 12 Nov 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-123139 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected product: Opera Neon. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-123139/ (Markdown: https://insights.sbomify.com/CVE-2026-123139/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-123139
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-123139
- OSV: https://osv.dev/vulnerability/CVE-2026-123139

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-123139/
Summaries are generated and may contain mistakes; the official description above is the record.