Envoy Proxy
CVE-2026-47774
HIGH
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
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Lifecycle Timeline
1DescriptionCVE.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.
AnalysisAI
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. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | 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. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | 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. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | 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. … |
| Remediation | 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). … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Inventory all Envoy instances and versions; configure HTTP/2 request logging and establish baseline memory metrics. …
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Same technique Denial Of Service
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