CVE
Opera Neon spoofed commands in MCP Hub allow browser takeover
- Exploited
- No known exploitation
- Fix
- See vendor advisory
- Who is exposed
- Not reported
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- FIRST's estimate of the chance attackers exploit it in the next 30 days, updated daily.What do these mean? →
- 0.12% · 1st percentile
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 11/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Opera Neon on macOS and Windows has a flaw where it fails to verify the source of messages on a communication channel. A local attacker who gets a malicious browser extension installed, with the user's involvement, can use it to take control of the browser by sending commands through MCP Hub to the built-in Browser Operator extension.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure?/25Unknown. No advisory context yet
- Reach?/20Unknown. No tracked technology or package matched
- Severity5.8/10CVSS 5.8
- No patch5/5No fixed version listed; see vendor advisory
What would change the score
- Would score about 66 if added to CISA KEV
- Would score about 61 if CISA's SSVC rates exploitation active
- Would score about 33 if advisories confirm default setups are exposed
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-123139 (Improper verification of the source of a communication channel vulnerability in Opera Neon on macOS and Windows allows a malicious browser…), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-123139 (entry last updated 2026-11-12):
Affected:
- Opera Neon: versions 1.0.0
Fixed versions: none listed yet.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-123139 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-123139 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://security.opera.com/en/improper-verification-of-source-of-a-communication-channel-opera-security-advisories/
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-123139
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-123139"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- Opera Neon
1.0.0
Evidence 3
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Link
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-123139
Is CVE-2026-123139 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-123139?
Neon: version 1.0.0.Source: cve.now feed data