Envoy Proxy
CVE-2026-47774
HIGH
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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ReconIdentify Envoy-fronted HTTP/2 endpoint
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DeliveryOpen downstream HTTP/2 connection
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ExploitSend requests with oversized HPACK-encoded cookie headers
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InstallBypass encoded-byte HPACK limits
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C2Force large decoded header allocations in Envoy
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ExecuteExhaust worker memory and trigger OOM kill
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ImpactDenial of service for backend services
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V2 - Validation and Business Logic Asymmetric resource consumption control
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| Exploitation Conditions | Target Envoy must be running an affected version (prior to 1.35.11/1.36.7/1.37.3/1.38.1) with downstream HTTP/2 enabled on a network-reachable listener, which is the default for typical edge and ingress configurations. No authentication, no user interaction, and no non-default configuration are required on Envoy's side; the attacker only needs the ability to establish HTTP/2 connections and send HPACK-compressed cookie/header payloads. Limiting factors: deployments that already terminate HTTP/2 at an upstream CDN/WAF and forward HTTP/1.1 to Envoy, or that have disabled downstream HTTP/2, are not exposed via this path; HTTP/3 and upstream-only HTTP/2 are not implicated by the advisory. |
| Impact | The CVSS 3.1 vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H scores 7.5 and is internally consistent with the description: a remote, unauthenticated attacker can reach the HTTP/2 listener over the network with low complexity and impact only availability. There is no EPSS score, KEV listing, or public POC referenced in the provided intelligence, so this is not confirmed actively exploited. However, Envoy commonly fronts production traffic at the edge of cloud-native deployments, so a single misbehaving client can plausibly OOM-kill a shared data-plane process, amplifying blast radius. SSVC-style read: exploitation status = none confirmed, automatable = likely yes (single HTTP/2 connection class of payloads), technical impact = partial (availability only). Treat as a high-priority availability bug for any internet-facing or multi-tenant Envoy fleet, but not an emergency RCE-class issue. |
| Exploit ScenarioDerived | An unauthenticated attacker on the internet opens an HTTP/2 connection to an Envoy-fronted service and sends requests carrying carefully crafted HPACK-encoded headers - particularly oversized cookie values - that stay within the encoded-byte HPACK block limit but expand to very large decoded header sets. Repeating this across requests or connections forces Envoy to allocate memory beyond its intended request header size cap, eventually exhausting the worker process's memory and triggering an OOM kill that takes the proxy (and the services behind it) offline. No public POC is referenced, but the bug class is straightforward to reproduce given the advisory description. |
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Alert meAnalysisAIv1 – Jun 17, 2026
Denial of service in Envoy versions prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1 allows unauthenticated remote clients to trigger excessive memory consumption via crafted HTTP/2 requests, potentially causing OOM termination of the Envoy process. The flaw stems from cookie header bytes bypassing request header size validation combined with HPACK limits being enforced only on encoded bytes. No public exploit identified at time of analysis, but the network-reachable, no-auth attack profile makes it a credible availability threat for edge proxies.
RemediationAI
Vendor-released patch: upgrade to Envoy 1.35.11, 1.36.7, 1.37.3, or 1.38.1 depending on your maintenance branch, as published in advisory GHSA-22m2-hvr2-xqc8 (https://github.com/envoyproxy/envoy/security/advisories/GHSA-22m2-hvr2-xqc8). The vendor states no complete workaround is known short of patching. Temporary mitigations called out by the project include disabling downstream HTTP/2 where operationally feasible (trade-off: loss of HTTP/2 multiplexing, higher latency, and broken clients that require HTTP/2 such as gRPC-web), enforcing stricter request header and cookie size limits at an upstream device or CDN before traffic reaches Envoy (trade-off: may break apps with large legitimate cookies/session tokens), and monitoring Envoy memory usage for abnormal growth under HTTP/2 traffic so OOM events can be correlated and rate-limited or auto-restarted.
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Technical ContextAI · show details
Envoy is a widely deployed L7 edge/service proxy used in service meshes (Istio, Consul) and ingress gateways. The vulnerability sits in Envoy's downstream HTTP/2 request processing path, specifically the interaction between Envoy's request header size accounting and the oghttp2/quiche HPACK decoder. HPACK (RFC 7541) compresses HTTP/2 headers, and the bug is twofold: Envoy excludes cookie header bytes from its header-size validation, and oghttp2/quiche enforces block limits on the wire-encoded (compressed) size rather than the decoded size. CWE-405 (Asymmetric Resource Consumption / Amplification) accurately captures the root cause - small compressed input yields large decoded allocations. Affected CPE is cpe:2.3:a:envoyproxy:envoy across all versions before the listed fix releases.
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable HTTP/2 listener, no auth or user interaction, low complexity to send crafted HPACK headers; impact limited to availability via OOM, with no confidentiality or integrity effect.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
DescriptionCVE.org
Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1, a vulnerability in Envoy's HTTP/2 downstream request processing allows an unauthenticated remote client to trigger excessive memory consumption, potentially resulting in OOM termination of the Envoy process and denial of service. The issue arises from the combination of two behaviors. First, cookie header bytes are not fully accounted for during request header size validation in Envoy. Second, HPACK header block limits in oghttp2/quiche are enforced on encoded bytes without a corresponding limit on total decoded header size. Together, these behaviors allow a malicious client to cause large decoded header allocations while bypassing the intended request header size protections. Versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1 contain a fix. No complete workaround is known short of applying a fix. Possible temporary mitigations include disabling downstream HTTP/2 where operationally feasible; enforcing stricter request header and cookie limits before traffic reaches Envoy; and monitoring Envoy memory usage for abnormal growth under HTTP/2 traffic.
Executive ViewAI
Envoy proxy versions prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1 contain a high-severity denial-of-service vulnerability that allows unauthenticated remote clients to crash the proxy through memory exhaustion via malformed HTTP/2 requests, with no public exploit identified at time of analysis. Organizations using Envoy in gateway or service mesh deployments face potential service outages, particularly without available patches.
No vendor-released patch identified at time of analysis. Interim mitigations: (1) enforce strict HTTP/2 header size limits via Envoy proxy.envoy.http2.max_header_size configuration, (2) implement connection-level rate limiting to throttle unauthenticated HTTP/2 traffic, (3) enable continuous monitoring of Envoy process memory utilization with automated alerting for anomalous growth, and (4) restrict HTTP/2 protocol access through network segmentation where feasible. These controls reduce risk but do not eliminate it and should be treated as temporary measures pending vendor patch release.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
GitHub
VulDB
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)CVE.org
Denial of service against HTTP/2 server implementations allows remote unauthenticated attackers to exhaust server resour
Envoy is an open source edge and service proxy designed for cloud-native applications. Rated critical severity (CVSS 9.8
An issue was discovered in Envoy 1.12.0. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable,
An issue was discovered in Envoy 1.12.0. Rated critical severity (CVSS 9.8), this vulnerability is remotely exploitable,
Envoy is an open source edge and service proxy designed for cloud-native applications. Rated critical severity (CVSS 9.1
Envoy is an open source edge and service proxy designed for cloud-native applications. Rated critical severity (CVSS 9.1
Envoy is an open source edge and service proxy designed for cloud-native applications. Rated critical severity (CVSS 9.1
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Envoy's RBAC filter improperly concatenates duplicate HTTP headers into comma-separated strings instead of validating ea
Envoy is a cloud-native high-performance edge/middle/service proxy. Rated high severity (CVSS 7.5), this vulnerability i
Envoy is a cloud-native high-performance edge/middle/service proxy. Rated high severity (CVSS 7.5), this vulnerability i
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