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Fencer Vulns
medium 5.8

CVE-2021-32778 json

Excessive CPU utilization when closing HTTP/2 streams

published 2021-08-24 5 y ago modified 2026-09-08 2 mo ago also BIT-envoy-2021-32778 , EUVD-2021-19542 , GHSA-3xh3-33v5-chcc

cvss
5.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.2%
EPSS 1.2% chance of exploitation in 30 days, percentile 69%
public exploits
0
none known

Summary

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.

Patch / fix

  • bitnami envoy 1.16.5, 1.17.4, 1.18.4, 1.19.1
  • envoyproxy envoy 1.16.5, 1.17.4, 1.18.4
  • servicemesh service mesh 2.1 2.1.0-5.el8
  • servicemesh-cni service mesh 2.1 2.1.0-5.el8
  • servicemesh-proxy service mesh 2.1 2.1.0-13.el8
  • servicemesh-grafana service mesh 2.1 7.2.1-2.el8
  • servicemesh-operator service mesh 2.1 2.1.0-4.el8
  • servicemesh-ratelimit service mesh 2.1 2.1.0-1.el8
  • servicemesh-prometheus service mesh 2.1 2.23.0-1.el8
  • servicemesh-proxy-wasm service mesh 2.1 2.1.0-13.el8

red hat advisories RHEA-2021:4051

  • istio Arch Linux 1.11.1-1

arch linux advisories AVG-2321

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-32778 updated cvss 7.5

envoyproxy/envoy: excessive CPU usage when handling a large number of HTTP/2 requests

  • Red Hat OpenShift Service Mesh 1 servicemesh-proxy Red Hat OpenShift Service Mesh 2.0 servicemesh-proxy
    affected: no fix available
  • Red Hat OpenShift Service Mesh 2.1 servicemesh 2.1.0-5.el8, servicemesh-cni 2.1.0-5.el8, servicemesh-proxy 2.1.0-13.el8, servicemesh-grafana 7.2.1-2.el8, servicemesh-operator 2.1.0-4.el8, servicemesh-ratelimit 2.1.0-1.el8, +4 more
    fixed: vendor fix RHEA-2021:4051

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.23% chance of exploitation in the next 30 days, higher than 69% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD 2.0 5.0 AV:N/AC:L/Au:N/C:N/I:N/A:P
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
bitnami envoy
>=1.16.0, <1.16.5
>=1.17.0, <1.17.4
>=1.18.0, <1.18.4
>=1.19.0, <1.19.1
1.16.5
1.17.4
1.18.4
1.19.1

Affected products

  • envoyproxy envoy

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.