CVE-2026-48743: CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in envoyproxy envoy
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.
AI Analysis
Technical Summary
The vulnerability (CVE-2026-48743) in Envoy proxy arises from inconsistent handling of HTTP/3 downstream requests that are complete at the transport layer but declare a nonzero Content-Length. Envoy translates these into HTTP/1 upstream requests with unresolved body debt. In upstream HTTP/1 deployments where the origin server responds before reading the full declared body and keeps the connection reusable, the next Envoy-generated upstream request's beginning can be consumed as the previous request's body. This leads to the origin parsing remaining bytes as a new HTTP/1 request, enabling request smuggling and route bypass scenarios. The vulnerability affects Envoy versions prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, where it has been fixed.
Potential Impact
An attacker could exploit this vulnerability to perform HTTP request smuggling, causing the origin server to misinterpret requests. This can lead to route bypass or desynchronization attacks, potentially allowing unauthorized access to backend resources or manipulation of request handling. The CVSS score of 7.5 (high severity) reflects the potential for information disclosure and integrity impact without availability impact.
Mitigation Recommendations
This vulnerability is fixed in Envoy versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1. Users should upgrade to these or later versions to remediate the issue. Patch status is confirmed by the version-based fixes; no other mitigation guidance is provided.
CVE-2026-48743: CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in envoyproxy envoy
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.
CVSS v3.1
Score 7.5high
Affected software
pkg:github/envoyproxy/envoyRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability (CVE-2026-48743) in Envoy proxy arises from inconsistent handling of HTTP/3 downstream requests that are complete at the transport layer but declare a nonzero Content-Length. Envoy translates these into HTTP/1 upstream requests with unresolved body debt. In upstream HTTP/1 deployments where the origin server responds before reading the full declared body and keeps the connection reusable, the next Envoy-generated upstream request's beginning can be consumed as the previous request's body. This leads to the origin parsing remaining bytes as a new HTTP/1 request, enabling request smuggling and route bypass scenarios. The vulnerability affects Envoy versions prior to 1.35.11, 1.36.7, 1.37.3, and 1.38.1, where it has been fixed.
Potential Impact
An attacker could exploit this vulnerability to perform HTTP request smuggling, causing the origin server to misinterpret requests. This can lead to route bypass or desynchronization attacks, potentially allowing unauthorized access to backend resources or manipulation of request handling. The CVSS score of 7.5 (high severity) reflects the potential for information disclosure and integrity impact without availability impact.
Mitigation Recommendations
This vulnerability is fixed in Envoy versions 1.35.11, 1.36.7, 1.37.3, and 1.38.1. Users should upgrade to these or later versions to remediate the issue. Patch status is confirmed by the version-based fixes; no other mitigation guidance is provided.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-22T19:10:35.747Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a3ec110d9e07477746fae3a
Added to database: 06/26/2026, 18:12:32 UTC
Last enriched: 07/03/2026, 22:23:54 UTC
Last updated: 08/10/2026, 00:41:17 UTC
Views: 159
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