CVE-2026-94439: Go Standard Library HTTP/1 Server Connection Desynchronization Vulnerability
Summary
CVE-2026-94439: HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http. Affects stdlib across 2 version ranges.
< 1.26.9
>= 1.27.0-0, < 1.27.2
Fixed in 1.26.9 or 1.27.2, depending on the release line you run. How to fix ↓
Also tracked for
- golang · Bitnami
The same CVE-2026-94439 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
The Go standard library provides essential packages for building web servers and clients, with 'net/http' being a core component for handling HTTP requests and responses. This library is widely used in Go applications for its simplicity and efficiency in managing HTTP connections. However, it is susceptible to a specific vulnerability that can lead to request smuggling under certain conditions.
Vulnerability Detail
The vulnerability arises when an HTTP server handler sends a 2xx response to an HTTP/1 CONNECT request without hijacking the connection. Instead of treating the connection as a tunnel, the server continues to read and serve requests as if it were still handling standard HTTP traffic. This misbehavior can lead to potential request smuggling, where an intermediate proxy misinterprets the connection state, allowing malicious actors to exploit the situation.
How To Fix
Latest published version: go1.25.5 as of 22 Oct 2026
go get stdlib@vgo1.25.5Upgrading to it may include breaking changes; the versions below are the minimum fixed release for this vulnerability.
If you can't move to the latest
The minimum fixed version depends on the release line you run.
-
< 1.26.91.26.9go get stdlib@v1.26.9 -
>= 1.27.0-0, < 1.27.21.27.2go get stdlib@v1.27.2
Tip — Not sure which release line you're on? Vulert can find the fix for the version you are using. Scan free →
Workaround
As a temporary workaround, ensure that your server properly hijacks connections after sending a 2xx response to a CONNECT request. This can be done by implementing a custom handler that explicitly manages the connection state to prevent the server from treating it as a standard HTTP connection.
Conclusion
CVE-2026-94439 is a significant vulnerability in the Go standard library that can lead to serious security issues if not addressed. It is crucial for developers using affected versions to update their libraries and implement proper connection management practices to mitigate risks.
See every vulnerability recorded for stdlib →
FAQ
CVE-2026-94439 is a vulnerability in the Go standard library's HTTP/1 server that can lead to connection desynchronization and potential request smuggling.
If your application uses the affected versions of the Go standard library, it may be vulnerable to request smuggling attacks, which can compromise the integrity of your HTTP communications.
Versions prior to 1.26.9 and 1.27.2 of the Go standard library are affected by this vulnerability.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
If immediate updates are not possible, implement a custom handler to manage connection states properly as a temporary workaround.
References
Related vulnerabilities
Recent vulnerabilities recorded for stdlib.
