What’s Vulnerable › Vulnerabilities

CVE-2021-39204: Excessive CPU usage in Pomerium

• Severity: medium (CVSS 5.0 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-09-09 · updated 2026-06-17
• Weakness: CWE-834

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.

Affected products

• envoyproxy envoy: through 1.16.4; from 1.17.0 before 1.17.4; from 1.18.0 before 1.18.4; 1.19.0 — fixed in 1.17.4, 1.18.4
• pomerium: before 0.14.8; 0.15.0 — fixed in 0.14.8

How to fix

Upgrade to a fixed version: envoyproxy envoy 1.17.4, 1.18.4; pomerium 0.14.8. Check the vendor advisory for mitigations.

References

• https://github.com/envoyproxy/envoy/security/advisories/GHSA-3xh3-33v5-chcc
• https://github.com/pomerium/pomerium/security/advisories/GHSA-5wjf-62hw-q78r
• https://groups.google.com/g/envoy-announce/c/5xBpsEZZDfE/m/wD05NZBbAgAJ
• https://github.com/envoyproxy/envoy/security/advisories/GHSA-3xh3-33v5-chcc
• https://github.com/pomerium/pomerium/security/advisories/GHSA-5wjf-62hw-q78r
• https://groups.google.com/g/envoy-announce/c/5xBpsEZZDfE/m/wD05NZBbAgAJ

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