Request Smuggling Vulnerability in Go HTTP Server
CVE-2026-94439

7.5HIGH

Key Information:

Vendor

Go Standard Library

Status
Net/http
Vendor
CVE Published:
8 October 2026

What is CVE-2026-94439?

This vulnerability occurs when a Go HTTP server improperly handles HTTP/1 CONNECT requests. Specifically, if the server responds with a 2xx status code without hijacking the connection, it erroneously keeps the connection open for further requests. This behavior leads to a scenario where request smuggling can occur, as an intermediate proxy may regard the data on the connection as being tunneled, while the server processes it as standard HTTP data. This discrepancy can potentially be exploited by attackers to manipulate HTTP requests and responses.

Affected Version(s)

net/http 0 < 1.26.9

net/http 1.27.0-0 < 1.27.2

References

https://go.dev/cl/847311
https://go.dev/issue/81744
https://groups.google.com/g/golang-announce/c/U2fTuyDJznI

CVSS V3.1

Score:
7.5
Severity:
HIGH
Confidentiality:
High
Integrity:
None
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Jakub Ciolek (https://ciolek.dev)
.