Description
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.
Published: 2026-10-08
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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History

Fri, 09 Oct 2026 16:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'}

 ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N'}

Fri, 09 Oct 2026 12:15:00 +0000

Type Values Removed Values Added
Weaknesses CWE-444
References
Metrics threat_severity

None

 cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N'}

threat_severity

Moderate

Fri, 09 Oct 2026 09:15:00 +0000

Type Values Removed Values Added
First Time appeared Go Standard Library
Go Standard Library net/http
Go Standard Library net/http/httputil
Vendors & Products Go Standard Library
Go Standard Library net/http
Go Standard Library net/http/httputil

Thu, 08 Oct 2026 23:00:00 +0000

Type Values Removed Values Added
Description 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.
Title HTTP/1 client connection desynchronization after CONNECT rejection in net/http
References

Subscriptions

Go Standard Library Net/http Net/http/httputil
cve-icon MITRE

Status: PUBLISHED

Assigner: Go

Published:

Updated: 2026-10-09T15:54:59.009Z

Reserved: 2026-06-23T15:10:49.354Z

Link: CVE-2026-56866

cve-icon Vulnrichment

Updated: 2026-10-09T15:50:23.374Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-08T23:17:01.620

Modified: 2026-10-09T16:35:35.900

Link: CVE-2026-56866

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-10-08T22:53:58Z

Links: CVE-2026-56866 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-09T18:00:12Z

Weaknesses
  • CWE-444

    Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')