CVE-2026-94439: HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-10-08 · updated 2026-10-09
Weakness: CWE-444

Description

When an HTTP server handler sends a 2xx response to an HTTP/1 CONNECT request and returns without hijacking the connection, the server improperly continues to read and serve requests from the connection. Since a 2xx response to an HTTP/1 CONNECT converts the connection into a tunnel, the server should not treat the connection as continuing to contain HTTP. The impact of this misbehavior is mostly limited to potential request smuggling, where an intermediate proxy considers the data on the connection to be tunneled and the server considers it to be HTTP.

Affected products

Go Stdlib: before 1.26.9; from 1.27.0-0 before 1.27.2 — fixed in 1.26.9, 1.27.2
Go standard library net/http: before 1.26.9; from 1.27.0-0 before 1.27.2 — fixed in 1.26.9, 1.27.2

How to fix

Upgrade to a fixed version: Go Stdlib 1.26.9, 1.27.2; Go standard library net/http 1.26.9, 1.27.2. Check the vendor advisory for mitigations.

References

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