CVE-2021-32778

Name: CVE-2021-32778
Creator: NVD / NIST
Published: 2021-08-24T21:15:09.553+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 1.23%

Last modified Jun 17, 2026

CVE-2021-32778 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions envoy’s procedure for resetting a HTTP/2 stream has O(N^2) complexity, leading to high CPU utilization when a large number of streams are reset. EPSS estimates a 1.23% chance of exploitation in the next 30 days.

Description

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions envoy’s procedure for resetting a HTTP/2 stream has O(N^2) complexity, leading to high CPU utilization when a large number of streams are reset. Deployments are susceptible to Denial of Service when Envoy is configured with high limit on H/2 concurrent streams. An attacker wishing to exploit this vulnerability would require a client opening and closing a large number of H/2 streams. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to reduce time complexity of resetting HTTP/2 streams. As a workaround users may limit the number of simultaneous HTTP/2 dreams for upstream and downstream peers to a low number, i.e. 100.

Metrics

CVSS 3.1

7.5/10

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

EPSS Probability

1.23%

65.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Envoyproxy	Envoy	>= 1.16.0, < 1.16.5
Envoyproxy	Envoy	>= 1.17.0, < 1.17.4
Envoyproxy	Envoy	>= 1.18.0, < 1.18.4
Envoyproxy	Envoy	1.19.0

References

https://github.com/envoyproxy/envoy/security/advisories/GHSA-3xh3-33v5-chccThird Party Advisory
https://www.envoyproxy.io/docs/envoy/v1.19.0/version_history/version_historyRelease Notes, Vendor Advisory
https://github.com/envoyproxy/envoy/security/advisories/GHSA-3xh3-33v5-chccThird Party Advisory
https://www.envoyproxy.io/docs/envoy/v1.19.0/version_history/version_historyRelease Notes, Vendor Advisory

Timeline

Published: Aug 24, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-32778?

How severe is CVE-2021-32778?

CVE-2021-32778 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.23% probability of exploitation in the next 30 days.

How do I fix CVE-2021-32778?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-32778?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST