# CVE-2021-21303: Injection attack in Helm

> Attackers can inject terminal escape sequences via unsanitized Helm chart metadata, potentially altering or obscuring terminal output.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 5 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** AZL-6470, BIT-helm-2021-21303, GHSA-c38g-469g-cmgx, GO-2022-1040, UBUNTU-CVE-2021-21303

## What is CVE-2021-21303?

CVE-2021-21303 is a medium-severity vulnerability in helm, published on 5 Feb 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

Helm is open-source software which is essentially "The Kubernetes Package Manager". Helm is a tool for managing Charts. Charts are packages of pre-configured Kubernetes resources. In Helm from version 3.0 and before version 3.5.2, there a few cases where data loaded from potentially untrusted sources was not properly sanitized. When a SemVer in the `version` field of a chart is invalid, in some cases Helm allows the string to be used "as is" without sanitizing. Helm fails to properly sanitized some fields present on Helm repository `index.yaml` files. Helm does not properly sanitized some fields in the `plugin.yaml` file for plugins In some cases, Helm does not properly sanitize the fields in the `Chart.yaml` file. By exploiting these attack vectors, core maintainers were able to send deceptive information to a terminal screen running the `helm` command, as well as obscure or alter information on the screen. In some cases, we could send codes that terminals used to execute higher-order logic, like clearing a terminal screen. Further, during evaluation, the Helm maintainers discovered a few other fields that were not properly sanitized when read out of repository index files. This fix remedies all such cases, and once again enforces SemVer2 policies on version fields. All users of the Helm 3 should upgrade to the fixed version 3.5.2 or later. Those who use Helm as a library should verify that they either sanitize this data on their own, or use the proper Helm API calls to sanitize the data.

Weakness: CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component)

## Which versions are affected by CVE-2021-21303?

4 open source packages ship an affected version, including helm.sh/helm/v3 and helm. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `helm.sh/helm/v3` | Go | From 3.0.0 | 3.5.2 |
| `helm.sh/helm/v3` | Go | From 3.0.0 | 3.5.2 |
| `helm.sh/helm/v3` | Go | From 3.0.0 | 3.5.2 |
| `helm` | Bitnami | From 3.0.0 | 3.5.2 |

Products: Helm Helm.

## How do I fix CVE-2021-21303?

Upgrade helm.sh/helm/v3 to 3.5.2 or later.

## Is CVE-2021-21303 being exploited?

There is no known exploitation of CVE-2021-21303 in the wild and no public exploit code.

## Other vulnerabilities in helm

- [CVE-2019-18658](https://insights.sbomify.com/CVE-2019-18658/): Helm Unsafe Link Following (critical 9.8)
- [CVE-2019-1010275](https://insights.sbomify.com/CVE-2019-1010275/): Helm Improper Certificate Validation (critical 9.8)
- [CVE-2019-25210](https://insights.sbomify.com/CVE-2019-25210/): Information disclosure in n/a (critical 9.1)
- [CVE-2025-53547](https://insights.sbomify.com/CVE-2025-53547/): Helm Chart Dependency Updating With Malicious Chart.yaml Content And Symlink Can Lead To Code Execution (high 8.5)
- [CVE-2020-11013](https://insights.sbomify.com/CVE-2020-11013/): lookup Function Information Discolosure in Helm (high 8.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21303 and fix it if it is affected.

What it is: CVE-2021-21303 is a medium-severity vulnerability in helm, published on 5 Feb 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-21303 in the wild and no public exploit code.

Affected packages and fixed versions:
- helm.sh/helm/v3 (Go): affected from 3.0.0; fixed in 3.5.2
- helm.sh/helm/v3 (Go): affected from 3.0.0; fixed in 3.5.2
- helm.sh/helm/v3 (Go): affected from 3.0.0; fixed in 3.5.2
- helm (Bitnami): affected from 3.0.0; fixed in 3.5.2

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-2021-21303/ (Markdown: https://insights.sbomify.com/CVE-2021-21303/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21303
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21303
- OSV: https://osv.dev/vulnerability/CVE-2021-21303

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21303/
Summaries are generated and may contain mistakes; the official description above is the record.