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Fencer Vulns
high 7.5

CVE-2026-73548 json

Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool

published 2026-09-21 48 d ago modified 2026-10-06 33 d ago also BIT-envoy-2026-73548 , EUVD-2026-84103 , GHSA-3vhp-c83q-jqc2

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 40%
public exploits
0
none known

Summary

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.

Patch / fix

  • bitnami envoy 1.36.10, 1.37.6, 1.38.4, 1.39.1
  • envoyproxy envoy 1.36.10, 1.37.6, 1.38.4, 1.39.1
  • istioctl openSUSE Tumbleweed 1.30.4-1.1

opensuse advisories openSUSE-SU-2026:11630-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-73548 updated cvss 7.5

envoy: envoy: connection poisoning through generic non-WebSocket HTTP upgrade requests

  • Red Hat OpenShift Service Mesh 3.0 openshift-service-mesh/istio-proxyv2-rhel9 1788296328
    fixed: vendor fix RHSA-2026:65106
  • Red Hat OpenShift Service Mesh 3.1 openshift-service-mesh/istio-proxyv2-rhel9 1788294715
    fixed: vendor fix RHSA-2026:65112
  • Red Hat OpenShift Service Mesh 3.2 openshift-service-mesh/istio-proxyv2-rhel9 1788329366
    fixed: vendor fix RHSA-2026:65113
  • Red Hat OpenShift Service Mesh 3.3 openshift-service-mesh/istio-proxyv2-rhel9 1788327866
    fixed: vendor fix RHSA-2026:65115
  • Red Hat OpenShift Service Mesh 3.4 openshift-service-mesh/istio-proxyv2-rhel9 1788333924
    fixed: vendor fix RHSA-2026:65121
  • Red Hat OpenShift Service Mesh 3.0 openshift-service-mesh/istio-cni-rhel9 1788292951, openshift-service-mesh/istio-pilot-rhel9 1788292901, openshift-service-mesh/istio-rhel9-operator 1788292915, openshift-service-mesh/istio-must-gather-rhel9 1788266981, openshift-service-mesh/istio-sail-operator-bundle 1788341233, openshift-service-mesh-dev-preview-beta/istio-ztunnel-rhel9 1788334488 Red Hat OpenShift Service Mesh 3.1 openshift-service-mesh/istio-cni-rhel9 1788294468, openshift-service-mesh/istio-pilot-rhel9 1788294578, openshift-service-mesh/istio-rhel9-operator 1788294534, openshift-service-mesh/istio-must-gather-rhel9 1788271718, openshift-service-mesh/istio-sail-operator-bundle 1788349977, openshift-service-mesh-tech-preview/istio-ztunnel-rhel9 1788334034 Red Hat OpenShift Service Mesh 3.2 openshift-service-mesh/istio-cni-rhel9 1788301003, openshift-service-mesh/istio-pilot-rhel9 1788301006, openshift-service-mesh/istio-ztunnel-rhel9 1788304137, openshift-service-mesh/istio-rhel9-operator 1788301001, openshift-service-mesh/istio-must-gather-rhel9 1788272030, openshift-service-mesh/istio-sail-operator-bundle 1788341754 Red Hat OpenShift Service Mesh 3.3 openshift-service-mesh/istio-cni-rhel9 1788301494, openshift-service-mesh/istio-pilot-rhel9 1788301650, openshift-service-mesh/istio-ztunnel-rhel9 1788286709, openshift-service-mesh/istio-rhel9-operator 1788301636, openshift-service-mesh/istio-must-gather-rhel9 1788262619, openshift-service-mesh/istio-sail-operator-bundle 1788342282 Red Hat OpenShift Service Mesh 3.4 openshift-service-mesh/istio-cni-rhel9 1788333736, openshift-service-mesh/istio-pilot-rhel9 1788333884, openshift-service-mesh/istio-ztunnel-rhel9 1788334411, openshift-service-mesh/istio-rhel9-operator 1788333618, openshift-service-mesh/istio-must-gather-rhel9 1788334442, openshift-service-mesh/istio-sail-operator-bundle 1788347718
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
yes
Technical impact
partial
Assessed
45 d ago

Exploit prediction

0.46% chance of exploitation in the next 30 days, higher than 40% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/envoyproxy/envoy/security/advisories/GHSA-3vhp-c83q-jqc2 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
bitnami envoy
<1.36.10
>=1.37.0, <1.37.6
>=1.38.0, <1.38.4
>=1.39.0, <1.39.1
1.36.10
1.37.6
1.38.4
1.39.1

Affected products

  • envoyproxy envoy

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.