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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 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 HTT

CVSS 7.5 · High EPSS 0.66% · P50

Affected Version Matrix 4

VendorProduct Version RangeStatus
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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I. Basic Information for CVE-2026-73548

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

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III. Intelligence Information for CVE-2026-73548

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

Other References for CVE-2026-73548 (5)

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

V. Comments for CVE-2026-73548

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