# CVE-2021-39204: Excessive CPU usage in Pomerium

> Attackers can cause excessive CPU usage and denial of service by resetting many HTTP/2 streams in Pomerium.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 9 Sep 2021
- **Updated:** 4 Aug 2024
- **Also known as:** BIT-envoy-2021-39204, GHSA-5wjf-62hw-q78r

## What is CVE-2021-39204?

CVE-2021-39204 is a high-severity denial of service vulnerability in Envoyproxy Envoy, published on 9 Sep 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Pomerium is an open source identity-aware access proxy. Envoy, which Pomerium is based on, incorrectly handles resetting of HTTP/2 streams with excessive complexity. This can lead to high CPU utilization when a large number of streams are reset. This can result in a DoS condition. Pomerium versions 0.14.8 and 0.15.1 contain an upgraded envoy binary with this vulnerability patched.

Weakness: CWE-834 (Excessive Iteration)

## Which versions are affected by CVE-2021-39204?

5 open source packages ship an affected version, including envoy and github.com/pomerium/pomerium. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `envoy` | Bitnami | All versions | 1.16.5, 1.17.4, 1.18.4, 1.19.1 |
| `github.com/pomerium/pomerium` | Go | All versions | 0.14.8 |
| `github.com/pomerium/pomerium` | Go | All versions | 0.14.8 |
| `github.com/pomerium/pomerium` | Go | From 0.15.0 | 0.15.1 |
| `github.com/pomerium/pomerium` | Go | From 0.15.0 | 0.15.1 |

Products: Envoyproxy Envoy, Pomerium Pomerium.

## How do I fix CVE-2021-39204?

Upgrade envoy to a fixed version for your release line: 1.16.5, 1.17.4, 1.18.4 or 1.19.1.

## Is CVE-2021-39204 being exploited?

There is no known exploitation of CVE-2021-39204 in the wild and no public exploit code.

## Other vulnerabilities in Envoyproxy Envoy

- [CVE-2022-29226](https://insights.sbomify.com/CVE-2022-29226/): Trivial authentication bypass in Envoy (critical 10.0)
- [CVE-2019-18801](https://insights.sbomify.com/CVE-2019-18801/): Memory corruption in n/a (critical 9.8)
- [CVE-2019-18802](https://insights.sbomify.com/CVE-2019-18802/): Security feature bypass in n/a (critical 9.8)
- [CVE-2020-35470](https://insights.sbomify.com/CVE-2020-35470/): Information disclosure in n/a (high 8.8)
- [CVE-2024-23324](https://insights.sbomify.com/CVE-2024-23324/): Envoy ext auth can be bypassed when Proxy protocol filter sets invalid UTF-8 metadata (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-39204 and fix it if it is affected.

What it is: CVE-2021-39204 is a high-severity denial of service vulnerability in Envoyproxy Envoy, published on 9 Sep 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-2021-39204 in the wild and no public exploit code.

Affected packages and fixed versions:
- envoy (Bitnami): affected all versions; fixed in 1.16.5, 1.17.4, 1.18.4, 1.19.1
- github.com/pomerium/pomerium (Go): affected all versions; fixed in 0.14.8
- github.com/pomerium/pomerium (Go): affected all versions; fixed in 0.14.8
- github.com/pomerium/pomerium (Go): affected from 0.15.0; fixed in 0.15.1
- github.com/pomerium/pomerium (Go): affected from 0.15.0; fixed in 0.15.1

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-2021-39204/ (Markdown: https://insights.sbomify.com/CVE-2021-39204/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-39204
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-39204
- OSV: https://osv.dev/vulnerability/CVE-2021-39204

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-39204/
Summaries are generated and may contain mistakes; the official description above is the record.