# CVE-2021-42023: Weak cryptography in ModelSim Simulation

> A sophisticated attacker can discover built-in private keys in ModelSim and Questa Simulation, bypassing IEEE 1735 protections to decrypt intellectual property data.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/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:** 14 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-x8jw-8x39-62fp

## What is CVE-2021-42023?

CVE-2021-42023 is a medium-severity vulnerability in Siemens ModelSim Simulation, published on 14 Dec 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A vulnerability has been identified in ModelSim Simulation (All versions), Questa Simulation (All versions). The RSA white-box implementation in affected applications insufficiently protects the built-in private keys that are required to decrypt electronic intellectual property (IP) data in accordance with the IEEE 1735 recommended practice. This could allow a sophisticated attacker to discover the keys, bypassing the protection intended by the IEEE 1735 recommended practice.

Weakness: CWE-522 (Insufficiently Protected Credentials)

## Which versions are affected by CVE-2021-42023?

It affects 2 products.


Products: Siemens Modelsim, Siemens Questa.

## How do I fix CVE-2021-42023?

No fix has been published for CVE-2021-42023 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-42023 being exploited?

There is no known exploitation of CVE-2021-42023 in the wild and no public exploit code.

Public exploit code:

- CVE-2021-42023 (github_poc): https://github.com/Geeoon/ModelSim-Decryptor

## Other vulnerabilities in Siemens ModelSim Simulation

- [CVE-2024-53977](https://insights.sbomify.com/CVE-2024-53977/): Code injection in ModelSim (medium 5.4)
- [CVE-2024-47194](https://insights.sbomify.com/CVE-2024-47194/): Other in ModelSim (medium 5.4)
- [CVE-2024-47195](https://insights.sbomify.com/CVE-2024-47195/): Path traversal in ModelSim (medium 5.4)
- [CVE-2024-47196](https://insights.sbomify.com/CVE-2024-47196/): Path traversal in ModelSim (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-42023 and fix it if it is affected.

What it is: CVE-2021-42023 is a medium-severity vulnerability in Siemens ModelSim Simulation, published on 14 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-2021-42023 in the wild and no public exploit code.

Affected product: Siemens ModelSim Simulation. 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-2021-42023/ (Markdown: https://insights.sbomify.com/CVE-2021-42023/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-42023
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-42023
- OSV: https://osv.dev/vulnerability/CVE-2021-42023

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-42023/
Summaries are generated and may contain mistakes; the official description above is the record.