CVE-2026-56866 (GCVE-0-2026-56866)

Vulnerability from cvelistv5 – Published: 2026-10-08 22:53 – Updated: 2026-10-09 15:54
VLAI
Title
HTTP/1 client connection desynchronization after CONNECT rejection in net/http
Summary
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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-09 15:53 UTC
CWE
  • CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
Go CNA under the Google root
CNA scorecard E 42/100 over 75 records in the last 180 days details
References
Impacted products
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 Create a notification for this product.
Go standard library net/http/httputil Affected: 0 , < 1.26.9 (semver)
Affected: 1.27.0-0 , < 1.27.2 (semver)
guessed Create a notification for this product.
Credits
Xclow3n (Rajat Raghav)
Show details on NVD website
To clipboard 

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}



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