HTTP/1 client connection desynchronization after CONNECT rejection in net/http
When http.Transport sends an HTTP/1 CONNECT request with a non-empty Request.Body, it writes the body directly to the connection without framing after the request headers. If the server rejects the CONNECT request with a non-2xx keep-alive response, Transport returns the connection to the idle pool. Because CONNECT requests do not have a request body, the server may interpret the trailing body bytes as a subsequent pipelined HTTP/1.1 request on the connection, leaving the pooled connection desynchronized and causing the next caller that reuses it to read the response to the injected request. In reverse proxies (including httputil.ReverseProxy) that forward CONNECT requests through a shared Transport, this can lead to cross-user response poisoning.
CVE-2026-56866
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-56866
net/http
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
net/http/httputil
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"vendor": "Go standard library",
"product": "net/http",
"versions": [
{
"status": "affected",
"version": "0",
"lessThan": "1.26.9",
"versionType": "semver"
},
{
"status": "affected",
"version": "1.27.0-0",
"lessThan": "1.27.2",
"versionType": "semver"
}
],
"packageName": "net/http",
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"programRoutines": [
{
"name": "persistConn.readLoop"
},
{
"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": "Get"
},
{
"name": "Head"
},
{
"name": "Post"
},
{
"name": "PostForm"
},
{
"name": "Transport.CloseIdleConnections"
},
{
"name": "Transport.NewClientConn"
},
{
"name": "Transport.RoundTrip"
},
{
"name": "http1ClientConn.Close"
},
{
"name": "http1ClientConn.RoundTrip"
}
]
},
{
"vendor": "Go standard library",
"product": "net/http/httputil",
"versions": [
{
"status": "affected",
"version": "0",
"lessThan": "1.26.9",
"versionType": "semver"
},
{
"status": "affected",
"version": "1.27.0-0",
"lessThan": "1.27.2",
"versionType": "semver"
}
],
"packageName": "net/http/httputil",
"collectionURL": "https://pkg.go.dev",
"defaultStatus": "unaffected",
"programRoutines": [
{
"name": "ReverseProxy.ServeHTTP"
},
{
"name": "DumpRequestOut"
}
]
}
]- Related CVEs
- CVE-2026-56866
Source reference:
/cveMetadata/cveId
Publisher severity
No explicit severity was provided.
- Event
- #16338 · Revision 1
- Added to Heist Feed
- Publisher date