CVE-2026-78660

Received Received - Intake

HTTP/2 Response Smuggling in Go

Publication date: 2026-10-08

Last updated on: 2026-10-08

Assigner: Go Project

Description

Historically, we have been rather lax about malformed framing-related headers in our HTTP/2 implementation, as they cannot interfere with HTTP/2 framing. However, this makes it possible for our HTTP/2 implementation to forward responses containing such headers to an HTTP/1 client when acting as a reverse proxy. If the HTTP/1 client also does not behave strictly enough, this can result in response smuggling.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-10-08

Last Modified

2026-10-08

Generated

2026-10-09

AI Q&A

2026-10-09

EPSS Evaluated

N/A

NVD

CVE-2026-78660

Affected Vendors & Products

Vendor	Product	Version / Range
Go	standard	library net/http 0
Go	standard	library net/http/internal/http2 1.27.0-0
golang.org/x/net	golang.org/x/net/http2	0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability involves improper handling of malformed HTTP/2 framing-related headers in Go's HTTP/2 implementation. When acting as a reverse proxy, the system may forward responses with such headers to an HTTP/1 client. If the HTTP/1 client also has lax parsing, this can lead to response smuggling, where malicious responses are injected into legitimate traffic.

Impact Analysis

This vulnerability could allow attackers to smuggle malicious responses through your systems, potentially leading to data breaches, unauthorized access, or misdirection of users to malicious content. It primarily affects systems using Go's HTTP/2 implementation as a reverse proxy.

Compliance Impact

This vulnerability could lead to data breaches or unauthorized access, which may violate GDPR's data protection requirements or HIPAA's safeguards for protected health information. Compliance could be impacted if sensitive data is exposed or altered due to response smuggling.

Mitigation Strategies

Update the Go standard library and golang.org/x/net/http2 to the latest patched versions to address the HTTP/2 response smuggling issue.

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