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7.5 High

CVE-2026-73548 Envoy is an open source edge and service proxy designed for cloud-native applications

Description

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 forwards data for a configured non-WebSocket HTTP upgrade before the upstream accepts the upgrade. An unauthenticated HTTP/2 client can place a complete HTTP/1.1 request in extended CONNECT data; Envoy downgrades the request, writes the data unframed to a keep-alive HTTP/1.1 upstream, and returns the socket to the shared pool while the smuggled response remains queued. A different downstream client can then receive the attacker's response. The relevant scope boundary is that webSocket upgrades, plain CONNECT, disabled backend keep-alive, per-downstream pools, and max_requests_per_connection set to 1 are not affected by the demonstrated path. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

Affected products and versions

Product Affected versions Fixed in
envoy 1.39 1.39.0 → < 1.39.1 1.39.1
envoy 1.38 1.38.0 → < 1.38.4 1.38.4
envoy 1.37 1.37.0 → < 1.37.6 1.37.6
envoy 1.36 earliest → < 1.36.10 1.36.10

References

Timeline

  1. Published
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Other CVEs of envoy

The 98 CVEs of envoy →
CVE-2026-73511 Envoy is an open source edge and service proxy designed for cloud-native applications 5.3 Medium CVE-2026-73553 Envoy is an open source edge and service proxy designed for cloud-native applications 7.5 High CVE-2026-73551 Envoy is an open source edge and service proxy designed for cloud-native applications 5.3 Medium CVE-2026-73546 Envoy is an open source edge and service proxy designed for cloud-native applications 7.4 High
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