How severe is CVE-2021-39204?

CVE-2021-39204 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-39204?

CVE-2021-39204 affects the following packages: github.com/pomerium/pomerium (Go), github.com/pomerium/pomerium (Go). Ecosystems affected: Go.

How do I fix CVE-2021-39204?

Update github.com/pomerium/pomerium to 0.14.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39204 is resolved across your whole dependency graph.

How do I detect CVE-2021-39204 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/pomerium/pomerium, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-39204 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-39204 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-39204 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-39204?

CVE-2021-39204 has an EPSS (Exploit Prediction Scoring System) score of 1.7%, placing it in the 77th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-39204?

CVE-2021-39204 is classified as CWE-834 (CWE-834). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-39204 published, and has it been updated?

CVE-2021-39204 was published on September 9, 2021 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2021-39204 — pomerium

HIGH

CVE-2021-39204 is a high-severity (CVSS 7.5) CWE-834 vulnerability in github.com/pomerium/pomerium. A fix is available for github.com/pomerium/pomerium — see the affected versions and patch details below.

Excessive CPU usage

Also known asBIT-envoy-2021-39204GHSA-5wjf-62hw-q78r

Published

Sep 9, 2021

Updated

Oct 20, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Nov 7, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs77th percentile — riskier than 77% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

2 pkgs affected

🐹github.com/pomerium/pomerium🐹github.com/pomerium/pomerium

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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.

Impact

This can result in a DoS condition.

Patches

Pomerium versions 0.14.8 and 0.15.1 contain an upgraded envoy binary with this vulnerability patched.

Workarounds

N/A

References

envoy GSA envoy CVE envoy announcement

For more information

If you have any questions or comments about this advisory:

Open an issue in pomerium/pomerium
Email us at [email protected]

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/pomerium/pomerium`	all versions	0.14.8`go get github.com/pomerium/pomerium@v0.14.8`
🐹Go	`github.com/pomerium/pomerium`	≥ 0.15.0&&< 0.15.1	0.15.1`go get github.com/pomerium/pomerium@v0.15.1`

Affected Products

2 products · 6 configurations

Application

envoyenvoyproxy

≥ 1.18.0 && ≤ 1.16.4

1 version

1.19.0

Application

pomeriumpomerium

< 0.14.8

1 version

0.15.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/pomerium/pomerium, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/pomerium/pomerium to 0.14.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39204 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

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. ### Impact This can result in a DoS condition. ### Patches Pomerium versions 0.14.8 and 0.15.1 contain an upgraded envoy binary with this vulnerability patched. ### Workarounds N/A ### References [envoy GSA](https://github.com/envoyproxy/envoy/security/advisories/GHSA-3xh3-33v5-chcc) [envoy CVE](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-32778) [envoy announcement](https://groups.google

O3 Security · Impact-Aware SCA

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Find it across Go, including transitive dependencies.

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CVSS Score

7.5/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE Classification

CWE-834CWE-834

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

OpenSSF Scorecard

Package health score

envoy

8.5/10

Code-Review10/10

Maintained10/10

Dependency-Update-Tool10/10

Branch-Protection4/10

Vulnerabilities0/10

Assessed Nov 6, 2026

Timeline

Disclosed

Sep 9, 2021

Last updated

Oct 20, 2026

Identifiers

CVE-2021-39204

GHSA-5wjf-62hw-q78r

BIT-envoy-2021-39204

References

Advisorygithub.com · GHSA 3xh3 33v5 chcc Advisorygithub.com · GHSA 5wjf 62hw q78r Advisorynvd.nist.gov · CVE 2021 39204 Webgroups.google.com · wD05NZBbAgAJ Packagegithub.com · pomerium

Related vulnerabilities

This CVE is high severity; 4 of 8 other CVEs affecting pomerium are rated as high or higher (top: critical).

CVE-2026-50285CVE-2024-47616CVE-2022-24797CVE-2024-39315CVE-2023-33189GHSA-j34v-3552-5r7jCVE-2021-41230CVE-2021-39206

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 20, 2026

CVE-2021-39204 — pomerium

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Impact

Patches

Workarounds

References

For more information

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

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