CVE-2026-94439 (GCVE-0-2026-94439)
Vulnerability from cvelistv5 – Published: 2026-10-08 22:53 – Updated: 2026-10-08 22:53
VLAI
EPSS
VEX
Title
HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http
Summary
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.
Severity
No CVSS data available.
CWE
- CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
References
Impacted products
1 product
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Go standard library | net/http |
Affected:
0 , < 1.26.9
(semver)
Affected: 1.27.0-0 , < 1.27.2 (semver) |
guessed |
{
"containers": {
"cna": {
"affected": [
{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "net/http",
"product": "net/http",
"programRoutines": [
{
"name": "chunkWriter.writeHeader"
},
{
"name": "CanonicalHeaderKey"
},
{
"name": "Client.CloseIdleConnections"
},
{
"name": "Client.Do"
},
{
"name": "Client.Get"
},
{
"name": "Client.Head"
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{
"name": "Client.Post"
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{
"name": "Client.PostForm"
},
{
"name": "ClientConn.Close"
},
{
"name": "ClientConn.RoundTrip"
},
{
"name": "Cookie.String"
},
{
"name": "Cookie.Valid"
},
{
"name": "CrossOriginProtection.AddInsecureBypassPattern"
},
{
"name": "CrossOriginProtection.AddTrustedOrigin"
},
{
"name": "CrossOriginProtection.Check"
},
{
"name": "Dir.Open"
},
{
"name": "Error"
},
{
"name": "Get"
},
{
"name": "Handle"
},
{
"name": "HandleFunc"
},
{
"name": "HandlerFunc.ServeHTTP"
},
{
"name": "Head"
},
{
"name": "Header.Add"
},
{
"name": "Header.Del"
},
{
"name": "Header.Get"
},
{
"name": "Header.Set"
},
{
"name": "Header.Values"
},
{
"name": "Header.Write"
},
{
"name": "Header.WriteSubset"
},
{
"name": "ListenAndServe"
},
{
"name": "ListenAndServeTLS"
},
{
"name": "NewRequest"
},
{
"name": "NewRequestWithContext"
},
{
"name": "NotFound"
},
{
"name": "ParseCookie"
},
{
"name": "ParseSetCookie"
},
{
"name": "ParseTime"
},
{
"name": "Post"
},
{
"name": "PostForm"
},
{
"name": "ProxyFromEnvironment"
},
{
"name": "ReadRequest"
},
{
"name": "ReadResponse"
},
{
"name": "Redirect"
},
{
"name": "Request.AddCookie"
},
{
"name": "Request.BasicAuth"
},
{
"name": "Request.Cookie"
},
{
"name": "Request.Cookies"
},
{
"name": "Request.CookiesNamed"
},
{
"name": "Request.FormFile"
},
{
"name": "Request.FormValue"
},
{
"name": "Request.MultipartReader"
},
{
"name": "Request.ParseForm"
},
{
"name": "Request.ParseMultipartForm"
},
{
"name": "Request.PostFormValue"
},
{
"name": "Request.Referer"
},
{
"name": "Request.SetBasicAuth"
},
{
"name": "Request.UserAgent"
},
{
"name": "Request.Write"
},
{
"name": "Request.WriteProxy"
},
{
"name": "Response.Cookies"
},
{
"name": "Response.Location"
},
{
"name": "Response.Write"
},
{
"name": "ResponseController.EnableFullDuplex"
},
{
"name": "ResponseController.Flush"
},
{
"name": "ResponseController.Hijack"
},
{
"name": "ResponseController.SetReadDeadline"
},
{
"name": "ResponseController.SetWriteDeadline"
},
{
"name": "Serve"
},
{
"name": "ServeContent"
},
{
"name": "ServeFile"
},
{
"name": "ServeFileFS"
},
{
"name": "ServeMux.Handle"
},
{
"name": "ServeMux.HandleFunc"
},
{
"name": "ServeMux.ServeHTTP"
},
{
"name": "ServeTLS"
},
{
"name": "Server.Close"
},
{
"name": "Server.ListenAndServe"
},
{
"name": "Server.ListenAndServeTLS"
},
{
"name": "Server.Serve"
},
{
"name": "Server.ServeTLS"
},
{
"name": "Server.SetKeepAlivesEnabled"
},
{
"name": "Server.Shutdown"
},
{
"name": "SetCookie"
},
{
"name": "Transport.CancelRequest"
},
{
"name": "Transport.Clone"
},
{
"name": "Transport.CloseIdleConnections"
},
{
"name": "Transport.NewClientConn"
},
{
"name": "Transport.RoundTrip"
},
{
"name": "body.Close"
},
{
"name": "body.Read"
},
{
"name": "bodyEOFSignal.Close"
},
{
"name": "bodyEOFSignal.Read"
},
{
"name": "bodyLocked.Read"
},
{
"name": "bufioFlushWriter.Write"
},
{
"name": "cancelTimerBody.Close"
},
{
"name": "cancelTimerBody.Read"
},
{
"name": "checkConnErrorWriter.Write"
},
{
"name": "chunkWriter.Write"
},
{
"name": "connReader.Read"
},
{
"name": "connectMethodKey.String"
},
{
"name": "expectContinueReader.Close"
},
{
"name": "expectContinueReader.Read"
},
{
"name": "extraHeader.Write"
},
{
"name": "fileHandler.ServeHTTP"
},
{
"name": "fileTransport.RoundTrip"
},
{
"name": "globalOptionsHandler.ServeHTTP"
},
{
"name": "gzipReader.Close"
},
{
"name": "gzipReader.Read"
},
{
"name": "http1ClientConn.Close"
},
{
"name": "http1ClientConn.RoundTrip"
},
{
"name": "http2ClientConn.RoundTrip"
},
{
"name": "http2Handler.ServeHTTP"
},
{
"name": "http2ResponseWriter.Flush"
},
{
"name": "http2ResponseWriter.FlushError"
},
{
"name": "http2ResponseWriter.Push"
},
{
"name": "http2RoundTripper.RoundTrip"
},
{
"name": "http3ServerHandler.ServeHTTP"
},
{
"name": "initALPNRequest.ServeHTTP"
},
{
"name": "loggingConn.Close"
},
{
"name": "loggingConn.Read"
},
{
"name": "loggingConn.Write"
},
{
"name": "maxBytesReader.Close"
},
{
"name": "maxBytesReader.Read"
},
{
"name": "onceCloseListener.Close"
},
{
"name": "persistConn.Read"
},
{
"name": "persistConnWriter.ReadFrom"
},
{
"name": "persistConnWriter.Write"
},
{
"name": "populateResponse.Write"
},
{
"name": "populateResponse.WriteHeader"
},
{
"name": "readTrackingBody.Close"
},
{
"name": "readTrackingBody.Read"
},
{
"name": "readWriteCloserBody.CloseWrite"
},
{
"name": "readWriteCloserBody.Read"
},
{
"name": "redirectHandler.ServeHTTP"
},
{
"name": "response.Flush"
},
{
"name": "response.FlushError"
},
{
"name": "response.Hijack"
},
{
"name": "response.ReadFrom"
},
{
"name": "response.Write"
},
{
"name": "response.WriteHeader"
},
{
"name": "response.WriteString"
},
{
"name": "serverHandler.ServeHTTP"
},
{
"name": "socksDialer.DialWithConn"
},
{
"name": "socksUsernamePassword.Authenticate"
},
{
"name": "stringWriter.WriteString"
},
{
"name": "timeoutHandler.ServeHTTP"
},
{
"name": "timeoutWriter.Write"
},
{
"name": "timeoutWriter.WriteHeader"
},
{
"name": "transportReadFromServerError.Error"
},
{
"name": "unencryptedHTTP2Request.ServeHTTP"
}
],
"vendor": "Go standard library",
"versions": [
{
"lessThan": "1.26.9",
"status": "affected",
"version": "0",
"versionType": "semver"
},
{
"lessThan": "1.27.2",
"status": "affected",
"version": "1.27.0-0",
"versionType": "semver"
}
]
}
],
"credits": [
{
"lang": "en",
"value": "Jakub Ciolek (https://ciolek.dev)"
}
],
"descriptions": [
{
"lang": "en",
"value": "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."
}
],
"problemTypes": [
{
"descriptions": [
{
"description": "CWE-444: Inconsistent Interpretation of HTTP Requests (\u0027HTTP Request/Response Smuggling\u0027)",
"lang": "en"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-10-08T22:53:59.976Z",
"orgId": "1bb62c36-49e3-4200-9d77-64a1400537cc",
"shortName": "Go"
},
"references": [
{
"url": "https://go.dev/cl/847311"
},
{
"url": "https://go.dev/issue/81744"
},
{
"url": "https://groups.google.com/g/golang-announce/c/U2fTuyDJznI"
},
{
"url": "https://pkg.go.dev/vuln/GO-2026-6613"
}
],
"title": "HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http"
}
},
"cveMetadata": {
"assignerOrgId": "1bb62c36-49e3-4200-9d77-64a1400537cc",
"assignerShortName": "Go",
"cveId": "CVE-2026-94439",
"datePublished": "2026-10-08T22:53:59.976Z",
"dateReserved": "2026-09-21T16:43:04.757Z",
"dateUpdated": "2026-10-08T22:53:59.976Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"nvd": {
"cve": {
"affected": [
{
"affectedData": [
{
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"packageName": "net/http",
"product": "net/http",
"programRoutines": [
{
"name": "chunkWriter.writeHeader"
},
{
"name": "CanonicalHeaderKey"
},
{
"name": "Client.CloseIdleConnections"
},
{
"name": "Client.Do"
},
{
"name": "Client.Get"
},
{
"name": "Client.Head"
},
{
"name": "Client.Post"
},
{
"name": "Client.PostForm"
},
{
"name": "ClientConn.Close"
},
{
"name": "ClientConn.RoundTrip"
},
{
"name": "Cookie.String"
},
{
"name": "Cookie.Valid"
},
{
"name": "CrossOriginProtection.AddInsecureBypassPattern"
},
{
"name": "CrossOriginProtection.AddTrustedOrigin"
},
{
"name": "CrossOriginProtection.Check"
},
{
"name": "Dir.Open"
},
{
"name": "Error"
},
{
"name": "Get"
},
{
"name": "Handle"
},
{
"name": "HandleFunc"
},
{
"name": "HandlerFunc.ServeHTTP"
},
{
"name": "Head"
},
{
"name": "Header.Add"
},
{
"name": "Header.Del"
},
{
"name": "Header.Get"
},
{
"name": "Header.Set"
},
{
"name": "Header.Values"
},
{
"name": "Header.Write"
},
{
"name": "Header.WriteSubset"
},
{
"name": "ListenAndServe"
},
{
"name": "ListenAndServeTLS"
},
{
"name": "NewRequest"
},
{
"name": "NewRequestWithContext"
},
{
"name": "NotFound"
},
{
"name": "ParseCookie"
},
{
"name": "ParseSetCookie"
},
{
"name": "ParseTime"
},
{
"name": "Post"
},
{
"name": "PostForm"
},
{
"name": "ProxyFromEnvironment"
},
{
"name": "ReadRequest"
},
{
"name": "ReadResponse"
},
{
"name": "Redirect"
},
{
"name": "Request.AddCookie"
},
{
"name": "Request.BasicAuth"
},
{
"name": "Request.Cookie"
},
{
"name": "Request.Cookies"
},
{
"name": "Request.CookiesNamed"
},
{
"name": "Request.FormFile"
},
{
"name": "Request.FormValue"
},
{
"name": "Request.MultipartReader"
},
{
"name": "Request.ParseForm"
},
{
"name": "Request.ParseMultipartForm"
},
{
"name": "Request.PostFormValue"
},
{
"name": "Request.Referer"
},
{
"name": "Request.SetBasicAuth"
},
{
"name": "Request.UserAgent"
},
{
"name": "Request.Write"
},
{
"name": "Request.WriteProxy"
},
{
"name": "Response.Cookies"
},
{
"name": "Response.Location"
},
{
"name": "Response.Write"
},
{
"name": "ResponseController.EnableFullDuplex"
},
{
"name": "ResponseController.Flush"
},
{
"name": "ResponseController.Hijack"
},
{
"name": "ResponseController.SetReadDeadline"
},
{
"name": "ResponseController.SetWriteDeadline"
},
{
"name": "Serve"
},
{
"name": "ServeContent"
},
{
"name": "ServeFile"
},
{
"name": "ServeFileFS"
},
{
"name": "ServeMux.Handle"
},
{
"name": "ServeMux.HandleFunc"
},
{
"name": "ServeMux.ServeHTTP"
},
{
"name": "ServeTLS"
},
{
"name": "Server.Close"
},
{
"name": "Server.ListenAndServe"
},
{
"name": "Server.ListenAndServeTLS"
},
{
"name": "Server.Serve"
},
{
"name": "Server.ServeTLS"
},
{
"name": "Server.SetKeepAlivesEnabled"
},
{
"name": "Server.Shutdown"
},
{
"name": "SetCookie"
},
{
"name": "Transport.CancelRequest"
},
{
"name": "Transport.Clone"
},
{
"name": "Transport.CloseIdleConnections"
},
{
"name": "Transport.NewClientConn"
},
{
"name": "Transport.RoundTrip"
},
{
"name": "body.Close"
},
{
"name": "body.Read"
},
{
"name": "bodyEOFSignal.Close"
},
{
"name": "bodyEOFSignal.Read"
},
{
"name": "bodyLocked.Read"
},
{
"name": "bufioFlushWriter.Write"
},
{
"name": "cancelTimerBody.Close"
},
{
"name": "cancelTimerBody.Read"
},
{
"name": "checkConnErrorWriter.Write"
},
{
"name": "chunkWriter.Write"
},
{
"name": "connReader.Read"
},
{
"name": "connectMethodKey.String"
},
{
"name": "expectContinueReader.Close"
},
{
"name": "expectContinueReader.Read"
},
{
"name": "extraHeader.Write"
},
{
"name": "fileHandler.ServeHTTP"
},
{
"name": "fileTransport.RoundTrip"
},
{
"name": "globalOptionsHandler.ServeHTTP"
},
{
"name": "gzipReader.Close"
},
{
"name": "gzipReader.Read"
},
{
"name": "http1ClientConn.Close"
},
{
"name": "http1ClientConn.RoundTrip"
},
{
"name": "http2ClientConn.RoundTrip"
},
{
"name": "http2Handler.ServeHTTP"
},
{
"name": "http2ResponseWriter.Flush"
},
{
"name": "http2ResponseWriter.FlushError"
},
{
"name": "http2ResponseWriter.Push"
},
{
"name": "http2RoundTripper.RoundTrip"
},
{
"name": "http3ServerHandler.ServeHTTP"
},
{
"name": "initALPNRequest.ServeHTTP"
},
{
"name": "loggingConn.Close"
},
{
"name": "loggingConn.Read"
},
{
"name": "loggingConn.Write"
},
{
"name": "maxBytesReader.Close"
},
{
"name": "maxBytesReader.Read"
},
{
"name": "onceCloseListener.Close"
},
{
"name": "persistConn.Read"
},
{
"name": "persistConnWriter.ReadFrom"
},
{
"name": "persistConnWriter.Write"
},
{
"name": "populateResponse.Write"
},
{
"name": "populateResponse.WriteHeader"
},
{
"name": "readTrackingBody.Close"
},
{
"name": "readTrackingBody.Read"
},
{
"name": "readWriteCloserBody.CloseWrite"
},
{
"name": "readWriteCloserBody.Read"
},
{
"name": "redirectHandler.ServeHTTP"
},
{
"name": "response.Flush"
},
{
"name": "response.FlushError"
},
{
"name": "response.Hijack"
},
{
"name": "response.ReadFrom"
},
{
"name": "response.Write"
},
{
"name": "response.WriteHeader"
},
{
"name": "response.WriteString"
},
{
"name": "serverHandler.ServeHTTP"
},
{
"name": "socksDialer.DialWithConn"
},
{
"name": "socksUsernamePassword.Authenticate"
},
{
"name": "stringWriter.WriteString"
},
{
"name": "timeoutHandler.ServeHTTP"
},
{
"name": "timeoutWriter.Write"
},
{
"name": "timeoutWriter.WriteHeader"
},
{
"name": "transportReadFromServerError.Error"
},
{
"name": "unencryptedHTTP2Request.ServeHTTP"
}
],
"vendor": "Go standard library",
"versions": [
{
"lessThan": "1.26.9",
"status": "affected",
"version": "0",
"versionType": "semver"
},
{
"lessThan": "1.27.2",
"status": "affected",
"version": "1.27.0-0",
"versionType": "semver"
}
]
}
],
"source": "security@golang.org"
}
],
"cveTags": [],
"descriptions": [
{
"lang": "en",
"value": "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."
}
],
"id": "CVE-2026-94439",
"lastModified": "2026-10-08T23:17:04.760",
"metrics": {},
"published": "2026-10-08T23:17:04.760",
"references": [
{
"source": "security@golang.org",
"url": "https://go.dev/cl/847311"
},
{
"source": "security@golang.org",
"url": "https://go.dev/issue/81744"
},
{
"source": "security@golang.org",
"url": "https://groups.google.com/g/golang-announce/c/U2fTuyDJznI"
},
{
"source": "security@golang.org",
"url": "https://pkg.go.dev/vuln/GO-2026-6613"
}
],
"sourceIdentifier": "security@golang.org",
"vulnStatus": "Received"
}
},
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-10-08T23:53:34+00:00",
"cve": "CVE-2026-94439",
"id": "CVE-2026-94439",
"initial_release_date": "2026-10-08T22:53:59.976000+00:00",
"product_status:known_affected": "341",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "net/http: golang: net/http: HTTP request smuggling via improper handling of HTTP/1 CONNECT responses",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-94439.json",
"version": "3"
}
}
}
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Sightings
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|---|
Nomenclature
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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