# CVE-2021-20156: Security feature bypass in Trendnet AC2600 TEW-827DRU

> Attackers can install malicious firmware on Trendnet routers due to missing signature validation, leading to full device compromise.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 30 Dec 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-6w2f-q3rq-jh8v

## What is CVE-2021-20156?

CVE-2021-20156 is a medium-severity vulnerability in Trendnet AC2600 TEW-827DRU, published on 30 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Trendnet AC2600 TEW-827DRU version 2.08B01 contains an improper access control configuration that could allow for a malicious firmware update. It is possible to manually install firmware that may be malicious in nature as there does not appear to be any signature validation done to determine if it is from a known and trusted source. This includes firmware updates that are done via the automated "check for updates" in the admin interface. If an attacker is able to masquerade as the update server, the device will not verify that the firmware updates downloaded are legitimate.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2021-20156?

It affects 1 product.


Products: Trendnet Tew-827dru Firmware.

## How do I fix CVE-2021-20156?

No fix has been published for CVE-2021-20156 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20156 being exploited?

There is no known exploitation of CVE-2021-20156 in the wild and no public exploit code.

## Other vulnerabilities in Trendnet AC2600 TEW-827DRU

- [CVE-2024-28354](https://insights.sbomify.com/CVE-2024-28354/): Command injection in n/a (critical 10.0)
- [CVE-2021-20151](https://insights.sbomify.com/CVE-2021-20151/): Auth bypass in Trendnet AC2600 TEW-827DRU (critical 10.0)
- [CVE-2021-20149](https://insights.sbomify.com/CVE-2021-20149/): Missing authorization in Trendnet AC2600 TEW-827DRU (critical 9.8)
- [CVE-2021-20155](https://insights.sbomify.com/CVE-2021-20155/): Hardcoded credentials in Trendnet AC2600 TEW-827DRU (critical 9.8)
- [CVE-2021-20158](https://insights.sbomify.com/CVE-2021-20158/): Auth bypass in Trendnet AC2600 TEW-827DRU (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20156 and fix it if it is affected.

What it is: CVE-2021-20156 is a medium-severity vulnerability in Trendnet AC2600 TEW-827DRU, published on 30 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-20156 in the wild and no public exploit code.

Affected product: Trendnet AC2600 TEW-827DRU. 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-2021-20156/ (Markdown: https://insights.sbomify.com/CVE-2021-20156/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20156
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20156
- OSV: https://osv.dev/vulnerability/CVE-2021-20156

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20156/
Summaries are generated and may contain mistakes; the official description above is the record.