# CVE-2021-35971: Deserialization in n/a

> Attackers can execute arbitrary code by exploiting unsafe deserialization in Veeam Backup and Replication's .NET remoting interface.

- **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:** 30 Jun 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-vmw6-j58p-9p55

## What is CVE-2021-35971?

CVE-2021-35971 is a critical unsafe deserialization vulnerability in n/a, published on 30 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Veeam Backup and Replication 10 before 10.0.1.4854 P20210609 and 11 before 11.0.0.837 P20210507 mishandles deserialization during Microsoft .NET remoting.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2021-35971?

It affects 1 product.


Products: Veeam Veeam Backup \& Replication.

## How do I fix CVE-2021-35971?

No fix has been published for CVE-2021-35971 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-35971 being exploited?

There is no known exploitation of CVE-2021-35971 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2024-40711](https://insights.sbomify.com/CVE-2024-40711/): Veeam Backup and Replication Deserialization (critical 9.8, exploited in the wild)
- [CVE-2022-26501](https://insights.sbomify.com/CVE-2022-26501/): Veeam Backup & Replication Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2022-26500](https://insights.sbomify.com/CVE-2022-26500/): Veeam Backup & Replication Remote Code Execution (high 8.8, exploited in the wild)
- [CVE-2023-27532](https://insights.sbomify.com/CVE-2023-27532/): Veeam Backup & Replication Cloud Connect Missing Authentication for Critical Function (high 7.5, exploited in the wild)
- [CVE-2026-21666](https://insights.sbomify.com/CVE-2026-21666/): Missing authorization in Backup and Replication (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-35971 and fix it if it is affected.

What it is: CVE-2021-35971 is a critical unsafe deserialization vulnerability in n/a, published on 30 Jun 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-2021-35971 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-2021-35971/ (Markdown: https://insights.sbomify.com/CVE-2021-35971/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-35971
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-35971
- OSV: https://osv.dev/vulnerability/CVE-2021-35971

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-35971/
Summaries are generated and may contain mistakes; the official description above is the record.