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TI-2026-51641 Aliases CVE-2026-73550

Envoy: HTTP/2 Discarded Host Header 200 GB Header-Copy OOM in Envoy

Priority HIGH 72CWE-401Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-401.

Summary

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy copies every decoded HTTP/2 Host header value before discarding it when :authority is already present. The discarded value bypasses saveHeader, so its bytes and count are not charged against request header limits. An unauthenticated client can use HPACK indexing to submit many references to a large Host value across a bounded number of streams, forcing extreme header-copy allocation and causing the proxy to be out-of-memory killed. The relevant scope boundary is that the demonstrated amplification uses HTTP/2 HPACK and the duplicate Host discard behavior. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00552 46th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed envoy (envoyproxy): 1.36.10, 1.37.6, 1.38.4 +1Red Hat: 5 advisories

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
envoyproxyenvoybefore 1.36.10; 1.37.0 to before 1.37.6; 1.38.0 to before 1.38.4; 1.39.0 to before 1.39.11.36.10, 1.37.6, 1.38.4, 1.39.1Patch availableCNA
  • envoy Vendorenvoyproxy Affected before 1.36.10; 1.37.0 to before 1.37.6; 1.38.0 to before 1.38.4; 1.39.0 to before 1.39.1 Fixed in 1.36.10, 1.37.6, 1.38.4, 1.39.1 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*before 1.36.10; 1.37.0 to before 1.37.6; 1.38.0 to before 1.38.4; 1.39.0 to before 1.39.1Vulnerableenvoyproxy
  • cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* Versions before 1.36.10; 1.37.0 to before 1.37.6; 1.38.0 to before 1.38.4; 1.39.0 to before 1.39.1 Vulnerable ·envoyproxy

Remediation

  • Fix · CNA envoy (envoyproxy) Fixed in 1.36.10, 1.37.6, 1.38.4, 1.39.1

Red Hat 5 advisories

  • RHSA-2026:65121 Released 2026-09-08 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 3.4.2
    • Red Hat OpenShift Service Mesh 3.4 registry.redhat.io/openshift-service-mesh/istio-cni-rhel9, registry.redhat.io/openshift-service-mesh/istio-pilot-rhel9, registry.redhat.io/openshift-service-mesh/istio-proxyv2-rhel9 +1
  • RHSA-2026:65115 Released 2026-09-08 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 3.3.7
    • Red Hat OpenShift Service Mesh 3.3 registry.redhat.io/openshift-service-mesh/istio-cni-rhel9, registry.redhat.io/openshift-service-mesh/istio-pilot-rhel9, registry.redhat.io/openshift-service-mesh/istio-proxyv2-rhel9 +1
  • RHSA-2026:65113 Released 2026-09-08 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 3.2.9
    • Red Hat OpenShift Service Mesh 3.2 registry.redhat.io/openshift-service-mesh/istio-cni-rhel9, registry.redhat.io/openshift-service-mesh/istio-pilot-rhel9, registry.redhat.io/openshift-service-mesh/istio-proxyv2-rhel9 +1
Show 2 more Red Hat advisories
  • RHSA-2026:65112 Released 2026-09-08 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 3.1.12
    • Red Hat OpenShift Service Mesh 3.1 registry.redhat.io/openshift-service-mesh/istio-cni-rhel9, registry.redhat.io/openshift-service-mesh/istio-pilot-rhel9, registry.redhat.io/openshift-service-mesh/istio-proxyv2-rhel9 +1
  • RHSA-2026:65106 Released 2026-09-08 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 3.0.15
    • Red Hat OpenShift Service Mesh 3.0 registry.redhat.io/openshift-service-mesh/istio-cni-rhel9, registry.redhat.io/openshift-service-mesh/istio-pilot-rhel9, registry.redhat.io/openshift-service-mesh/istio-proxyv2-rhel9 +1

Vendor assessments

Red Hat

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

ProductStatusPlan or fix
Red Hat OpenShift Service Mesh 3.0Fixed RHSA-2026:65106
Red Hat OpenShift Service Mesh 3.1Fixed RHSA-2026:65112
Red Hat OpenShift Service Mesh 3.2Fixed RHSA-2026:65113
Red Hat OpenShift Service Mesh 3.3Fixed RHSA-2026:65115
Red Hat OpenShift Service Mesh 3.4Fixed RHSA-2026:65121
Not affected: 5 products
  • Red Hat OpenShift Service Mesh 3.0
  • Red Hat OpenShift Service Mesh 3.1
  • Red Hat OpenShift Service Mesh 3.2
  • Red Hat OpenShift Service Mesh 3.3
  • Red Hat OpenShift Service Mesh 3.4

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-73550

References

Exploit 1

Patch 4

Other 4

  • 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