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CVE-2026-73548— Envoy: Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool

Quick assessment

Affected

envoyproxy envoy

Exploitation

No confirmed in-the-wild exploitation; assess based on exposure

Recommended action

Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Envoy 是一个专为云原生应用设计的开源边缘和服务代理。在 1.36.10、1.37.6、1.38.4 和 1.39.1 之前，Envoy 在上游服务尚未接受非 WebSocket HTTP 升级请求时，就提前转发了该升级请求的数据。一个未经身份验证的 HTTP/2 客户端可以在扩展的 CONNECT（extended CONNECT）数据中嵌入一个完整的 HTTP/1.1 请求。Envoy 会将该请求降级处理，将数据以无帧（unframed）方式写入一个保持连接（keep-alive）的 HTTP/1.1 上

CVSS 7.5 · High EPSS 0.46% · P40 Updated Sep 28, 2026

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 4

Vendor	Product	Version Range	Status
envoyproxy	envoy	`< 1.36.10`	affected
		`>= 1.37.0, < 1.37.6`	affected
		`>= 1.38.0, < 1.38.4`	affected
		`>= 1.39.0, < 1.39.1`	affected

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Vulnerability Information

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Vulnerability Title

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

Source: CVE Program / CVE List V5

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.

Source: CVE Program / CVE List V5

CVSS Information

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Source: CVE Program / CVE List V5

Vulnerability Type

HTTP请求的解释不一致性(HTTP请求私运)

Source: CVE Program / CVE List V5

Affected Products

Vendor	Product	Affected Versions	CPE	Subscribe
envoyproxy	envoy	< 1.36.10	-

II. Public POCs for CVE-2026-73548

#	POC Description	Source Link	Shenlong Link

AI-Generated POC Premium

No public POC found.

III. Intelligence Information for CVE-2026-73548

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Patches & Fixes for CVE-2026-73548 (4)

🔗 http: prevent generic upgrade connection poisoning · envoyproxy/envoy@bd6711f · GitHub Read full article x_refsource_MISC
🔗 http: prevent generic upgrade connection poisoning · envoyproxy/envoy@4633b8c · GitHub Read full article x_refsource_MISC
🔗 http: prevent generic upgrade connection poisoning · envoyproxy/envoy@3098556 · GitHub Read full article x_refsource_MISC
🔗 http: prevent generic upgrade connection poisoning · envoyproxy/envoy@3c79985 · GitHub Read full article x_refsource_MISC

Other References for CVE-2026-73548 (5)

🔗 Release v1.38.4 · envoyproxy/envoy · GitHub Read full article x_refsource_MISC
🔗 Release v1.37.6 · envoyproxy/envoy · GitHub Read full article x_refsource_MISC
🔗 Release v1.39.1 · envoyproxy/envoy · GitHub Read full article x_refsource_MISC
🔗 Release v1.36.10 · envoyproxy/envoy · GitHub Read full article x_refsource_MISC
🔗 Cross-user response poisoning via a generic (non-WebSocket) HTTP upgrade on Envoy's shared backend pool · Advisory · envoyproxy/envoy · GitHub Read full article x_refsource_CONFIRM

https://www.cve.org/CVERecord?id=CVE-2026-73548

Same Patch Batch · envoyproxy · 2026-09-21 · 13 CVEs total

CVE-2026-73550	7.5 HIGH	Envoy: HTTP/2 Discarded Host Header 200 GB Header-Copy OOM in Envoy
CVE-2026-73512	7.5 HIGH	Envoy: use-after-free in QUIC on internal redirects
CVE-2026-73553	7.5 HIGH	Envoy: RBAC Authorization Bypass via Path Parameters
CVE-2026-73513	7.5 HIGH	Envoy: oghttp2 upstream trailers incorrect handling
CVE-2026-73547	7.5 HIGH	Envoy ext_authz: request `:path` pseudoheader dereferenced w/o null check
CVE-2026-73552	7.5 HIGH	Envoy: HTTP RBAC safe_regex can fail open on RFC-valid obs-text header values
CVE-2026-73546	7.4 HIGH	Envoy: Stored XSS in Admin Stats Interface (/stats?format=html)
CVE-2026-48521	5.9 MEDIUM	Envoy: HTTP/3 connection pool selection null-derefs in ProdClusterManagerFactory::allocate
CVE-2026-50572	5.9 MEDIUM	Envoy: ext_authz - RawHttpClientImpl onSuccess 0x0 segfault
CVE-2026-73511	5.3 MEDIUM	Envoy: Potential path-matching/authentication bypass when using Envoy in combination with
CVE-2026-73549	5.3 MEDIUM	Envoy - Incomplete fix for CVE-2026-26310: copyInternetAddressAndPort crashes on scoped IP
CVE-2026-73551	5.3 MEDIUM	Envoy: Path normalization does not handle dot and dotdot segments with parameters

IV. Related Vulnerabilities

Same product: envoy

Same vendor: envoyproxy

Same weakness: CWE-444