# CVE-2021-31921: Missing authorization in n/a

> Attackers can bypass authorization checks to access unexpected cluster services when AUTO_PASSTHROUGH routing is configured.

- **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:** Yes
- **Published:** 2 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-3j84-jghj-gqwg, RHSA-2021:2061, RHSA-2021:2085

## What is CVE-2021-31921?

CVE-2021-31921 is a critical missing authorization vulnerability in n/a, published on 2 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Istio before 1.8.6 and 1.9.x before 1.9.5 contains a remotely exploitable vulnerability where an external client can access unexpected services in the cluster, bypassing authorization checks, when a gateway is configured with AUTO_PASSTHROUGH routing configuration.

Weakness: CWE-862 (Missing Authorization)

## Which versions are affected by CVE-2021-31921?

It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `servicemesh` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-citadel` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-galley` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-istioctl` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-mixc` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-mixs` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-pilot-agent` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-pilot-discovery` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh-sidecar-injector` | Red Hat:service_mesh:1.1::el8 | All versions | 0:1.1.15-4.el8 |
| `servicemesh` | Red Hat:service_mesh:2.0::el8 | All versions | 0:2.0.5-3.el8 |
| `servicemesh-istioctl` | Red Hat:service_mesh:2.0::el8 | All versions | 0:2.0.5-3.el8 |
| `servicemesh-mixc` | Red Hat:service_mesh:2.0::el8 | All versions | 0:2.0.5-3.el8 |
| `servicemesh-mixs` | Red Hat:service_mesh:2.0::el8 | All versions | 0:2.0.5-3.el8 |
| `servicemesh-pilot-agent` | Red Hat:service_mesh:2.0::el8 | All versions | 0:2.0.5-3.el8 |
| `servicemesh-pilot-discovery` | Red Hat:service_mesh:2.0::el8 | All versions | 0:2.0.5-3.el8 |

Products: Istio Istio.

## How do I fix CVE-2021-31921?

Upgrade to a fixed version.

## Is CVE-2021-31921 being exploited?

There is no known exploitation of CVE-2021-31921 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2021-34824](https://insights.sbomify.com/CVE-2021-34824/): Information disclosure in n/a (high 8.8)
- [CVE-2026-31837](https://insights.sbomify.com/CVE-2026-31837/): Istio JWKS resolver to prevent private key material from being exposed when JWKS fetch fails. (high 8.7)
- [CVE-2021-39155](https://insights.sbomify.com/CVE-2021-39155/): Authorization Policy Bypass Due to Case Insensitive Host Comparison (high 8.3)
- [CVE-2021-39156](https://insights.sbomify.com/CVE-2021-39156/): Fragments in Path May Lead to Authorization Policy Bypass (high 8.1)
- [CVE-2022-39388](https://insights.sbomify.com/CVE-2022-39388/): Istio may allow identity impersonation if user has localhost access (high 7.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-31921 and fix it if it is affected.

What it is: CVE-2021-31921 is a critical missing authorization vulnerability in n/a, published on 2 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-2021-31921 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-2021-31921/ (Markdown: https://insights.sbomify.com/CVE-2021-31921/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-31921
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-31921
- OSV: https://osv.dev/vulnerability/CVE-2021-31921

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-31921/
Summaries are generated and may contain mistakes; the official description above is the record.