CVE-2026-73548

7.5 HIGHpublic exploit available

Published 2026-09-21 · Updated 2026-09-21

AI risk analysis

Summary: The flaw allows an unauthenticated HTTP/2 client to smuggle a complete HTTP/1.1 request and response through Envoy, potentially intercepting sensitive data. This matters because it can lead to unauthorized access and data exposure.
Exploitability: Exploitation requires an attacker to send a specific HTTP/2 request with CONNECT data; preconditions include the target running an affected version of Envoy without proper configuration to mitigate this issue.
Blast radius: If exploited, this could result in significant data breaches and unauthorized access across multiple downstream clients sharing the same connection pool.
Prioritized remediation: Upgrade to Envoy versions 1.36.10, 1.37.6, 1.38.4, or 1.39.1 immediately to mitigate this vulnerability.

httpproxysmugglingupgradepatch

Analysis generated locally by qwen2.5:7b-instruct (no data left the box). AI-assisted — verify against primary sources before acting.

NVD 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.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Weaknesses

CWE-444

Public exploit & PoC references

All references

Source data: NVD (nvd.nist.gov), public domain. Exploit-DB.ai adds local AI analysis for defensive use only.

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