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CVE-2026-48743— Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length

Quick assessment

Affected
envoyproxy envoy
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Envoy Proxy Envoy是Envoy Proxy团队的应用网关。 Envoy Proxy Envoy 1.35.11之前版本、1.36.7之前版本、1.37.3之前版本和1.38.1之前版本存在输入验证错误漏洞，该漏洞源于HTTP/3请求处理问题，可能导致下游请求被错误翻译为上游HTTP/1请求，从而造成路由绕过和请求解同步。

CVSS 7.5 · High EPSS 0.30% · P20

Possible ATT&CK Techniques 1 AI

T1071 · Application Layer Protocol

Affected Version Matrix 4

VendorProduct Version RangeStatus
envoyproxy envoy >= 1.38.0, < 1.38.1 affected
>= 1.37.0, < 1.37.3 affected
>= 1.36.0, < 1.36.7 affected
>= 1.35.0, < 1.35.11 affected
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I. Basic Information for CVE-2026-48743

Vulnerability Information
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Vulnerability Title
Envoy: HTTP/3 to HTTP/1 request smuggling via headers-only request with nonzero Content-Length
Source: CVE Program / CVE List V5
Vulnerability Description
Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, Envoy can translate a downstream HTTP/3 request that is complete at the transport layer (HEADERS with FIN / headers-only close) but still carries a nonzero Content-Length into a complete upstream HTTP/1 request with unresolved body debt. In an HTTP/1 upstream deployment where the origin replies before reading the declared body and keeps the connection reusable, the beginning of the next Envoy-generated upstream request can be consumed as the first request's body. The remaining bytes are then parsed by the origin as a new HTTP/1 request. This was reproduced as a route-bypass/desync: direct /pwn was denied by Envoy, but the second downstream H3 stream received the response for backend-parsed GET /pwn HTTP/1.1. This vulnerability is fixed in 1.35.11, 1.36.7, 1.37.3, and 1.38.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/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
Vulnerability Title
Envoy Proxy Envoy 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Envoy Proxy Envoy是Envoy Proxy团队的应用网关。 Envoy Proxy Envoy 1.35.11之前版本、1.36.7之前版本、1.37.3之前版本和1.38.1之前版本存在输入验证错误漏洞，该漏洞源于HTTP/3请求处理问题，可能导致下游请求被错误翻译为上游HTTP/1请求，从而造成路由绕过和请求解同步。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
envoyproxy envoy >= 1.38.0, < 1.38.1 -

II. Public POCs for CVE-2026-48743

# POC Description Source Link Shenlong Link
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default-local-qwen3.6 · 14893 chars
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III. Intelligence Information for CVE-2026-48743

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Vendor Advisories for CVE-2026-48743 (1)

Same Patch Batch · envoyproxy · 2026-06-26 · 14 CVEs total

CVE-2026-48042 7.5 HIGH Envoy: Stack overflow in destructor of highly nested JSON
CVE-2026-48044 7.5 HIGH Envoy Zstd Decompressor: Ratio Check at Wrong Loop Depth lead to memory explosion
CVE-2026-47220 7.5 HIGH Envoy: Segmentation fault when using %REQUESTED_SERVER_NAME% in log format
CVE-2026-47775 6.8 MEDIUM Envoy OAuth2 Filter: Padding Oracle via AES-256-CBC Cookie Decryption
CVE-2026-47204 6.5 MEDIUM Envoy: grpc_stats filter segfault on Connect protocol requests to direct_response routes
CVE-2026-47207 6.5 MEDIUM Envoy crashes if multiple unexpected ext_proc responses are packed into one gRPC message
CVE-2026-47221 5.9 MEDIUM Envoy: Null pointer deref in internal redirects
CVE-2026-48497 5.9 MEDIUM Envoy: Abnormal process termination in DNS UDP filter
CVE-2026-48706 5.9 MEDIUM Envoy Heap Buffer Overflow in TcpStatsdSink
CVE-2026-47205 5.9 MEDIUM Envoy: ext_authz Use-After-Free during Stream Teardown with Per-Route Overrides
CVE-2026-48090 5.9 MEDIUM Envoy HTTP: OAuth2 filter late async token completion after stream teardown (UAF / crash r
CVE-2026-47692 4.8 MEDIUM Envoy: PROXY Protocol v2 header generator emits "skipped" TLVs, causing 65 KB attacker-con
CVE-2026-47778 4.4 MEDIUM Envoy: Embedded NUL in TLS DNS SAN Truncation in the Default TLS Certificate Validator. (A

IV. Related Vulnerabilities

Same product: envoy
Same vendor: envoyproxy
Same weakness: CWE-444

V. Comments for CVE-2026-48743

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