TI-2025-40101 Aliases CVE-2025-64763 GHSA-rj35-4m94-77jh

Envoy forwards early CONNECT data in TCP proxy mode

LOW 24CWE-693Published 2025-12-03 · Updated 2025-12-03

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: Security bypass
Confidentiality · integrity · availability: Low · None · None
Fix status: Partial Red Hat: 2 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA, GitHub and Red Hat. Impact type from CWE-693.

Summary

Envoy is a high-performance edge/middle/service proxy. In 1.33.12, 1.34.10, 1.35.6, 1.36.2, and earlier, when Envoy is configured in TCP proxy mode to handle CONNECT requests, it accepts client data before issuing a 2xx response and forwards that data to the upstream TCP connection. If a forwarding proxy upstream from Envoy then responds with a non-2xx status, this can cause a de-synchronized CONNECT tunnel state. By default Envoy continues to allow early CONNECT data to avoid disrupting existing deployments. The envoy.reloadable_features.reject_early_connect_data runtime flag can be set to reject CONNECT requests that send data before a 2xx response when intermediaries upstream from Envoy may reject establishment of a CONNECT tunnel.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00323 25th percentileScored 2026-11-07

Fix Partial github.com/envoyproxy/envoy (Go): 1.36.3, 1.35.7, 1.34.11 +1Red Hat: 2 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: No
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
envoyproxy	envoy	1.36.0 – 1.36.2; 1.35.0 – 1.35.6; 1.34.0 – 1.34.10; up to 1.33.12	—	No fix listed	CNA
—	github.com/envoyproxy/envoy (Go)	1.36.0 to before 1.36.3	1.36.3	Patch available	GHSA-rj35-4m94-77jh
—	github.com/envoyproxy/envoy (Go)	1.35.0 to before 1.35.7	1.35.7	Patch available	GHSA-rj35-4m94-77jh
—	github.com/envoyproxy/envoy (Go)	1.34.0 to before 1.34.11	1.34.11	Patch available	GHSA-rj35-4m94-77jh
—	github.com/envoyproxy/envoy (Go)	before 1.33.13	1.33.13	Patch available	GHSA-rj35-4m94-77jh

envoy Vendorenvoyproxy Affected 1.36.0 – 1.36.2; 1.35.0 – 1.35.6; 1.34.0 – 1.34.10; up to 1.33.12 Fixed in — No fix listed CNA
github.com/envoyproxy/envoy (Go) Vendor— Affected 1.36.0 to before 1.36.3 Fixed in 1.36.3 Patch available GHSA-rj35-4m94-77jh
github.com/envoyproxy/envoy (Go) Vendor— Affected 1.35.0 to before 1.35.7 Fixed in 1.35.7 Patch available GHSA-rj35-4m94-77jh
github.com/envoyproxy/envoy (Go) Vendor— Affected 1.34.0 to before 1.34.11 Fixed in 1.34.11 Patch available GHSA-rj35-4m94-77jh
github.com/envoyproxy/envoy (Go) Vendor— Affected before 1.33.13 Fixed in 1.33.13 Patch available GHSA-rj35-4m94-77jh

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:envoyproxy:envoy::::::::	before 1.33.13; 1.34.0 to before 1.34.11; 1.35.0 to before 1.35.7; 1.36.0 to before 1.36.3	Vulnerable	envoyproxy

cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* Versions before 1.33.13; 1.34.0 to before 1.34.11; 1.35.0 to before 1.35.7; 1.36.0 to before 1.36.3 Vulnerable ·envoyproxy

Remediation

Fix · GHSA-rj35-4m94-77jh github.com/envoyproxy/envoy (Go) Fixed in 1.36.3 Advisory →
Fix · GHSA-rj35-4m94-77jh github.com/envoyproxy/envoy (Go) Fixed in 1.35.7 Advisory →
Fix · GHSA-rj35-4m94-77jh github.com/envoyproxy/envoy (Go) Fixed in 1.34.11 Advisory →
Fix · GHSA-rj35-4m94-77jh github.com/envoyproxy/envoy (Go) Fixed in 1.33.13 Advisory →

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

Product	Status	Plan or fix
OpenShift Service Mesh 2	Affected	No fix yet: Fix deferred
OpenShift Service Mesh 3	Affected	No fix yet: Fix deferred

Timeline

2026-10-02 Threatist record created from CVE-2025-64763
2026-10-03 Alias added: GHSA-rj35-4m94-77jh

References

TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
TI-2024-20001 HTTP/2: CPU exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
TI-2024-18524 HTTP/2: memory exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
TI-2023-12215 Envoy client may fake the header `x-envoy-original-path` CVSS 3.1CRITICAL 9.1
TI-2023-18002 Envoy vulnerable to OAuth2 credentials exploit with permanent validity CVSS 3.1CRITICAL 9.8

See all 126 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences