# CVE-2021-27734: Auth bypass in n/a

> Remote attackers can change existing user credentials in Hirschmann HiOS and HiSecOS devices, leading to unauthorized access and privilege escalation.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 17 May 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-r6q8-h627-r6p2

## What is CVE-2021-27734?

CVE-2021-27734 is a critical authentication bypass vulnerability in n/a, published on 17 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Hirschmann HiOS 07.1.01, 07.1.02, and 08.1.00 through 08.5.xx and HiSecOS 03.3.00 through 03.5.01 allow remote attackers to change the credentials of existing users.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2021-27734?

It affects 2 products.


Products: Belden Hirschmann Hios, Belden Hisecos.

## How do I fix CVE-2021-27734?

No fix has been published for CVE-2021-27734 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27734 being exploited?

There is no known exploitation of CVE-2021-27734 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2020-6994](https://insights.sbomify.com/CVE-2020-6994/): Memory corruption in HiOS for the following devices RSP, RSPE, RSPS, RSPL, MSP, EES, EES, EESX, GRS, OS, RED (critical 9.8)
- [CVE-2020-9307](https://insights.sbomify.com/CVE-2020-9307/): Denial of service in n/a (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27734 and fix it if it is affected.

What it is: CVE-2021-27734 is a critical authentication bypass vulnerability in n/a, published on 17 May 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-27734 in the wild and no public exploit code.

Affected product: n/a. 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-2021-27734/ (Markdown: https://insights.sbomify.com/CVE-2021-27734/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27734
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27734
- OSV: https://osv.dev/vulnerability/CVE-2021-27734

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27734/
Summaries are generated and may contain mistakes; the official description above is the record.