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TI-2021-12445 Aliases CVE-2021-32778

Excessive CPU utilization when closing HTTP/2 streams

Priority LOW 35CWE-834Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
None · None · High
Fix status
Partial Red Hat: 1 fixed, 2 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat.

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.

Why it matters now

EPSS 0.0123 69th percentileScored 2026-11-07
Fix Partial envoy (envoyproxy): 1.19.1, 1.18.4, 1.17.4 +1Red Hat: 1 fixed, 2 without a fix

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
envoyproxyenvoy1.19.0 to before 1.19.1; 1.18.0 to before 1.18.4; 1.17.0 to before 1.17.4; 1.16.0 to before 1.16.51.19.1, 1.18.4, 1.17.4, 1.16.5Patch availableCNA
  • envoy Vendorenvoyproxy Affected 1.19.0 to before 1.19.1; 1.18.0 to before 1.18.4; 1.17.0 to before 1.17.4; 1.16.0 to before 1.16.5 Fixed in 1.19.1, 1.18.4, 1.17.4, 1.16.5 Patch available CNA

CPE configurations NVD · 2

CPEVersionsRoleVendor
cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*1.16.0 to before 1.16.5; 1.17.0 to before 1.17.4; 1.18.0 to before 1.18.4Vulnerableenvoyproxy
cpe:2.3:a:envoyproxy:envoy:1.19.0:*:*:*:*:*:*:*1.19.0Vulnerableenvoyproxy
  • cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* Versions 1.16.0 to before 1.16.5; 1.17.0 to before 1.17.4; 1.18.0 to before 1.18.4 Vulnerable ·envoyproxy
  • cpe:2.3:a:envoyproxy:envoy:1.19.0:*:*:*:*:*:*:* Versions 1.19.0 Vulnerable ·envoyproxy

Remediation

  • Fix · CNA envoy (envoyproxy) Fixed in 1.19.1, 1.18.4, 1.17.4, 1.16.5

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
OpenShift Service Mesh 1AffectedNo fix yet
OpenShift Service Mesh 2.0AffectedNo fix yet
OpenShift Service Mesh 2.1Fixed—

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-32778

References

Advisory 2

  • TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
  • TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
  • TI-2024-20001 HTTP/2: CPU exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
  • TI-2024-18524 HTTP/2: memory exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
  • TI-2023-12215 Envoy client may fake the header `x-envoy-original-path` CVSS 3.1CRITICAL 9.1
  • TI-2023-18002 Envoy vulnerable to OAuth2 credentials exploit with permanent validity CVSS 3.1CRITICAL 9.8
See all 126 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences