FKIE_CVE-2026-56866

Vulnerability from fkie_nvd - Published: 2026-10-08 23:17 - Updated: 2026-10-09 16:35
Severity
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
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.
References
security@golang.orghttps://go.dev/cl/847306
security@golang.orghttps://go.dev/issue/81740
security@golang.orghttps://groups.google.com/g/golang-announce/c/U2fTuyDJznI
security@golang.orghttps://pkg.go.dev/vuln/GO-2026-6605
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "collectionURL": "https://pkg.go.dev",
          "defaultStatus": "unaffected",
          "packageName": "net/http",
          "product": "net/http",
          "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",
          "versions": [
            {
              "lessThan": "1.26.9",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThan": "1.27.2",
              "status": "affected",
              "version": "1.27.0-0",
              "versionType": "semver"
            }
          ]
        },
        {
          "collectionURL": "https://pkg.go.dev",
          "defaultStatus": "unaffected",
          "packageName": "net/http/httputil",
          "product": "net/http/httputil",
          "programRoutines": [
            {
              "name": "ReverseProxy.ServeHTTP"
            },
            {
              "name": "DumpRequestOut"
            }
          ],
          "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 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."
    }
  ],
  "id": "CVE-2026-56866",
  "lastModified": "2026-10-09T16:35:35.900",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-56866",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-10-09T15:53:00.591143Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-10-08T23:17:01.620",
  "references": [
    {
      "source": "security@golang.org",
      "url": "https://go.dev/cl/847306"
    },
    {
      "source": "security@golang.org",
      "url": "https://go.dev/issue/81740"
    },
    {
      "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-2026-6605"
    }
  ],
  "sourceIdentifier": "security@golang.org",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-444"
        }
      ],
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "type": "Secondary"
    }
  ]
}



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