GO-2026-6613 BIT-golang-2026-94439 CVE-2026-94439

HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http

High Go

Severity: 7.5 / 10; High · CVSS 3.1
Exploit chance (EPSS): 0.41%; Chance of exploitation in the next 30 days. Higher than 35.77% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-444 Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Fix: 1.27.2; Upgrade stdlib to this version or later

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 versions

Go

Package	Vulnerable	Fixed in
stdlib	`< 1.26.9` `>= 1.27.0-0, < 1.27.2`	`1.26.9` `1.27.2`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

stdlib Go → `1.27.2`

go

go get stdlib@v1.27.2 && go mod tidy

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: None
Availability: None

Weakness

CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

How to prevent it

Implementation: Use a web server that employs a strict HTTP parsing procedure, such as Apache [REF-433].
Implementation: Use only SSL communication.
Implementation: Terminate the client session after each request.
System Configuration: Turn all pages to non-cacheable.

References

Fixes and patches

go.dev/cl/847311

Issue reports

go.dev/issue/81744

Timeline

Oct 8, 2026 Published
Oct 16, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-4374-p667-p6c8 HTTP/2 rapid reset can cause excessive work in net/http	High Known exploited	Also affects stdlib
CVE-2020-0601 Certificate validation bypass on Windows in crypto/x509	High Known exploited	Also affects stdlib
RUSTSEC-2026-0382 Distrust compromised intermediate certificates in crypto/x509	Medium	Also affects stdlib
GO-2026-6609 Lack of limit on size of parsed Range headers in net/http	High	Also affects stdlib
GO-2026-6608 Memory limit bypass when parsing MIME headers in net/textproto, mime/multipart	High	Also affects stdlib
GO-2026-6607 Reject malformed ECH outer extension references in crypto/tls	High	Also affects stdlib
GO-2026-6604 Root.Mkdir(All) can follow junctions out of the root on Windows in os	Critical	Also affects stdlib
GO-2026-6600 Recognize yield as regexp preceder keyword in html/template	Medium	Also affects stdlib

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

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