Vulnerability 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 Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Envoyproxy | Envoy | < 1.36.10 |
Related Weaknesses (CWE)
References
- https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671Patch
- https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bPatch
- https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140bPatch
- https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0Patch
- https://github.com/envoyproxy/envoy/releases/tag/v1.36.10Release Notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.37.6Release Notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.38.4Release Notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.39.1Release Notes
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2ExploitVendor Advisory
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2ExploitVendor Advisory
FAQ
What is CVE-2026-73548?
CVE-2026-73548 is a vulnerability with a CVSS score of 7.5 (HIGH). 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 bef...
How severe is CVE-2026-73548?
CVE-2026-73548 has been rated HIGH with a CVSS base score of 7.5/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-73548?
Check the references section above for vendor advisories and patch information. Affected products include: Envoyproxy Envoy.