# CVE-2021-27256: Command injection in R7800

> Network-adjacent attackers can execute arbitrary code as root on NETGEAR R7800 routers by exploiting a command injection flaw in the rc_service parameter.

- **Severity:** High 8.8 (`CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-7j9h-j7vq-452x

## What is CVE-2021-27256?

CVE-2021-27256 is a high-severity command injection vulnerability in Netgear D7800 Firmware, published on 5 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of NETGEAR R7800 firmware version 1.0.2.76. Although authentication is required to exploit this vulnerability, the existing authentication mechanism can be bypassed. The specific flaw exists within the handling of the rc_service parameter provided to apply_save.cgi. The issue results from the lack of proper validation of a user-supplied string before using it to execute a system call. An attacker can leverage this vulnerability to execute code in the context of root. Was ZDI-CAN-12355.

Weakness: CWE-78 (Improper Neutralization of Special Elements used in an OS Command)

## Which versions are affected by CVE-2021-27256?

It affects 43 products.


Products: Netgear Br200 Firmware, Netgear Br500 Firmware, Netgear D7800 Firmware, Netgear Ex6100v2 Firmware, Netgear Ex6150v2 Firmware, Netgear Ex6250 Firmware, Netgear Ex6400 Firmware, Netgear Ex6400v2 Firmware, Netgear Ex6410 Firmware, Netgear Ex6420 Firmware, Netgear Ex7300 Firmware, Netgear Ex7300v2 Firmware, Netgear Ex7320 Firmware, Netgear Ex7700 Firmware, Netgear Ex8000 Firmware, Netgear Lbr20 Firmware, Netgear R7800 Firmware, Netgear R8900 Firmware, Netgear R9000 Firmware, Netgear Rbk12 Firmware and 23 more.

## How do I fix CVE-2021-27256?

No fix has been published for CVE-2021-27256 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27256 being exploited?

There is no known exploitation of CVE-2021-27256 in the wild and no public exploit code.

## Other vulnerabilities in Netgear D7800 Firmware

- [CVE-2021-27251](https://insights.sbomify.com/CVE-2021-27251/): Other in R7800 (high 8.8)
- [CVE-2021-27252](https://insights.sbomify.com/CVE-2021-27252/): Command injection in R7800 (high 8.8)
- [CVE-2021-27253](https://insights.sbomify.com/CVE-2021-27253/): Command injection in R7800 (high 8.8)
- [CVE-2021-27257](https://insights.sbomify.com/CVE-2021-27257/): Other in R7800 (medium 6.5)
- [CVE-2021-27254](https://insights.sbomify.com/CVE-2021-27254/): Hardcoded credentials in R7800 (medium 6.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27256 and fix it if it is affected.

What it is: CVE-2021-27256 is a high-severity command injection vulnerability in Netgear D7800 Firmware, published on 5 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-27256 in the wild and no public exploit code.

Affected product: Netgear D7800 Firmware. 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-2021-27256/ (Markdown: https://insights.sbomify.com/CVE-2021-27256/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27256
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27256
- OSV: https://osv.dev/vulnerability/CVE-2021-27256

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27256/
Summaries are generated and may contain mistakes; the official description above is the record.