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CVE-2026-73548

7.5 · HIGH

Envoy is an open source edge and service proxy designed for cloud-native applications.

Published Sep 21, 2026envoyproxyCWE-444EPSS 0.46%

Overview

CVE-2026-73548 is a high-severity vulnerability affecting envoyproxy envoy. It was published on September 21, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories and patches from envoyproxy. Update envoy to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
envoyproxyenvoy>= 0, < 1.36.10Affected

References

GitHubgithub.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361GitHubgithub.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2bGitHubgithub.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91cGitHubgithub.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766GitHubgithub.com/envoyproxy/envoy/releases/tag/v1.36.10GitHubgithub.com/envoyproxy/envoy/releases/tag/v1.37.6GitHubgithub.com/envoyproxy/envoy/releases/tag/v1.38.4GitHubgithub.com/envoyproxy/envoy/releases/tag/v1.39.1GitHubgithub.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2GitHubgithub.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2

How CyberStrike helps

Frequently asked questions

What is CVE-2026-73548?

CVE-2026-73548 is a high-severity vulnerability affecting envoyproxy envoy. It was published on September 21, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-73548?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-73548?

Check the references section for vendor advisories and patches from envoyproxy. Update envoy to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-73548?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-73548 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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