CVE-2026-73548Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool
Updated under an hour ago ()
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No exploitation reported and no EPSS estimate yet.
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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
- 7.5 HIGH (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
- Weakness (CWE)
- CWE-444
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Analyzed
- Record last updated
- Sep 24, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
envoyproxy envoy envoyproxy:envoy (from the name) | before 1.36.10; from 1.37.0, < 1.37.6; from 1.38.0, < 1.38.4; from 1.39.0, < 1.39.1 | CNA record |
envoyproxy envoy envoyproxy:envoy | before 1.36.10; from 1.37.0 before 1.37.6; from 1.38.0 before 1.38.4; from 1.39.0 before 1.39.1 | NVD |
References
- https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2x-refsource-confirm, exploit, vendor-advisory
- https://github.com/envoyproxy/envoy/commit/309855626966cff176155c821043ed3b44671361x-refsource-misc, patch
- https://github.com/envoyproxy/envoy/commit/3c7998545a9c9fb3933a4bc1907d92f0e752bc2bx-refsource-misc, patch
- https://github.com/envoyproxy/envoy/commit/4633b8cce3d15b8734eefe232e30c12b0140b91cx-refsource-misc, patch
- https://github.com/envoyproxy/envoy/commit/bd6711f2617658e28dfa3df3dace6bfe3cfc0766x-refsource-misc, patch
- https://github.com/envoyproxy/envoy/releases/tag/v1.36.10x-refsource-misc, release-notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.37.6x-refsource-misc, release-notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.38.4x-refsource-misc, release-notes
- https://github.com/envoyproxy/envoy/releases/tag/v1.39.1x-refsource-misc, release-notes
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.