No exploitation reportedFix available

CVE-2021-39204

Q: Is CVE-2021-39204 actively exploited?

Active exploitation of CVE-2021-39204 has not been confirmed. Its EPSS score was 1.7% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-39204?

CVE-2021-39204 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-09-09
Fixed in1.18.4 · 1.17.4
WeaknessCWE-834

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2021-09-0922:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-39204?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-39204?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Envoy

Branch	Affected	Fixed in	Source
1.18	≥ 1.18.0, < 1.18.4	1.18.4	NVD
1.17	≥ 1.17.0, < 1.17.4	1.17.4	NVD
1.16	≤ 1.16.4	no fix published	NVD
1.19	= 1.19.0	no fix published	NVD

Pomerium

Branch	Affected	Fixed in	Source
0.14	< 0.14.8	0.14.8	NVD
0.15	= 0.15.0	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Envoy to 1.18.4 · 1.17.4

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CNACVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
CNAweakness (CWE)CWE-834read 2026-10-23
NVDweakness (CWE)CWE-834read 2026-10-23
FIRST EPSSEPSS score1.7 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-09-09
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-39204?

Is CVE-2021-39204 actively exploited?

Active exploitation of CVE-2021-39204 has not been confirmed. Its EPSS score was 1.7% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

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

CVE-2021-39204 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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