EUVD-2026-95421Published

HTTP/1 client connection desynchronization after CONNECT rejection in net/http

Collected exploitation and prediction evidence

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

cve-program · CVE-2026-56866

Published

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.

Source published: 8 Oct 2026 22:53:58 UTC
Source modified: 9 Oct 2026 15:54:59 UTC
Observed here: 23 Oct 2026 15:48:27 UTC
Source terms: CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

euvd · EUVD-2026-95421

Published

EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.

Original publisher date fields

datePublished: Oct 8, 2026, 10:53:58 PM

dateUpdated: Oct 9, 2026, 3:54:59 PM

24 related source bulletins · separate from aliases

SUSE-SU-2026:24239-1: Security update for go1.26

CVE-2026-56857 · CVE-2026-56866 · CVE-2026-78659 · CVE-2026-78660 · CVE-2026-78667 · CVE-2026-94439 · CVE-2026-94440 · CVE-2026-94444 · CVE-2026-94447 · CVE-2026-94448 · CVE-2026-97030 · CVE-2026-97031 · CVE-2026-97032

openSUSE-SU-2026:22093-1: Security update for go1.27

CVE-2026-56857 · CVE-2026-56866 · CVE-2026-78659 · CVE-2026-78660 · CVE-2026-78663 · CVE-2026-78667 · CVE-2026-78669 · CVE-2026-94439 · CVE-2026-94440 · CVE-2026-94444 · CVE-2026-94447 · CVE-2026-94448 · CVE-2026-97030 · CVE-2026-97031 · CVE-2026-97032

RHSA-2026:92509: Red Hat Security Advisory: Red Hat OpenShift Service Mesh 3.3.9

CVE-2026-56857 · CVE-2026-56866 · CVE-2026-78663 · CVE-2026-78667 · CVE-2026-78669 · CVE-2026-94439 · CVE-2026-94440 · CVE-2026-94448 · CVE-2026-97030 · CVE-2026-97031 · CVE-2026-97032 · CVE-2026-111943

openSUSE-SU-2026:22095-1: Security update for go1.26

openSUSE-SU-2026:12093-1: go1.26-1.26.9-1.1 on GA media

openSUSE-SU-2026:12112-1: rclone-1.75.2-1.1 on GA media

CVE-2026-56857 · CVE-2026-56866 · CVE-2026-78659 · CVE-2026-78660 · CVE-2026-78663 · CVE-2026-78667 · CVE-2026-78669 · CVE-2026-84445 · CVE-2026-94439 · CVE-2026-94440 · CVE-2026-94444 · CVE-2026-94447 · CVE-2026-94448 · CVE-2026-97030 · CVE-2026-97031 · CVE-2026-97032

RHSA-2026:87043: Red Hat Security Advisory: golang security, bug fix, and enhancement update

CVE-2026-56866 · CVE-2026-78659 · CVE-2026-78660 · CVE-2026-78663 · CVE-2026-78667 · CVE-2026-78669 · CVE-2026-94439 · CVE-2026-94440 · CVE-2026-94444 · CVE-2026-94447 · CVE-2026-94448 · CVE-2026-97030 · CVE-2026-97031 · CVE-2026-97032 · CVE-2026-111943

RHSA-2026:92497: Red Hat Security Advisory: Red Hat OpenShift Service Mesh 3.2.11

RHSA-2026:86196: Red Hat Security Advisory: golang security, bug fix, and enhancement update

openSUSE-SU-2026:12101-1: go1.27-1.27.2-1.1 on GA media

WID-SEC-W-2026-3841: Golang Go: Mehrere Schwachstellen

RHSA-2026:86093: Red Hat Security Advisory: golang security, bug fix, and enhancement update

RHSA-2026:87246: Red Hat Security Advisory: go-toolset:rhel8 security, bug fix, and enhancement update

CVE-2024-45336 · CVE-2025-4673 · CVE-2025-22866 · CVE-2025-22874 · CVE-2025-68121 · CVE-2026-27137 · CVE-2026-27143 · CVE-2026-27144 · CVE-2026-27145 · CVE-2026-32280 · CVE-2026-32281 · CVE-2026-32282 · CVE-2026-32283 · CVE-2026-33810 · CVE-2026-33811 · CVE-2026-33814 · CVE-2026-33818 · CVE-2026-39820 · CVE-2026-39821 · CVE-2026-42499 · CVE-2026-42504 · CVE-2026-56853 · CVE-2026-56858 · CVE-2026-56859 · CVE-2026-56860 · CVE-2026-56862 · CVE-2026-56866 · CVE-2026-78659 · CVE-2026-78660 · CVE-2026-78663 · CVE-2026-78667 · CVE-2026-78669 · CVE-2026-94439 · CVE-2026-94440 · CVE-2026-94444 · CVE-2026-94447 · CVE-2026-94448 · CVE-2026-97030 · CVE-2026-97031 · CVE-2026-97032 · CVE-2026-111943

RHSA-2026:92480: Red Hat Security Advisory: Red Hat OpenShift Service Mesh 3.1.14

RHSA-2026:87041: Red Hat Security Advisory: golang security, bug fix, and enhancement update

RHSA-2026:92516: Red Hat Security Advisory: Red Hat OpenShift Service Mesh 3.4.4

RHSA-2026:87245: Red Hat Security Advisory: go-toolset:rhel8 security, bug fix, and enhancement update

RHSA-2026:86203: Red Hat Security Advisory: go-toolset:rhel8 security, bug fix, and enhancement update

RHSA-2026:87042: Red Hat Security Advisory: golang security, bug fix, and enhancement update

RHSA-2026:90994: Red Hat Security Advisory: go-toolset:rhel8 security, bug fix, and enhancement update

CVE-2024-45336 · CVE-2025-22866 · CVE-2025-22874 · CVE-2025-68121 · CVE-2026-27137 · CVE-2026-27143 · CVE-2026-27144 · CVE-2026-27145 · CVE-2026-32280 · CVE-2026-32281 · CVE-2026-32282 · CVE-2026-32283 · CVE-2026-33810 · CVE-2026-33811 · CVE-2026-33814 · CVE-2026-33818 · CVE-2026-39820 · CVE-2026-39821 · CVE-2026-42499 · CVE-2026-42504 · CVE-2026-56853 · CVE-2026-56858 · CVE-2026-56859 · CVE-2026-56860 · CVE-2026-56862 · CVE-2026-56866 · CVE-2026-78659 · CVE-2026-78660 · CVE-2026-78663 · CVE-2026-78667 · CVE-2026-78669 · CVE-2026-94439 · CVE-2026-94440 · CVE-2026-94444 · CVE-2026-94447 · CVE-2026-94448 · CVE-2026-97030 · CVE-2026-97031 · CVE-2026-97032 · CVE-2026-111943

RHSA-2026:87040: Red Hat Security Advisory: golang security, bug fix, and enhancement update

msrc_CVE-2026-56866: HTTP/1 client connection desynchronization after CONNECT rejection in net/http

CVE-2026-56866

SUSE-SU-2026:24237-1: Security update for go1.27

RHSA-2026:92451: Red Hat Security Advisory: Red Hat OpenShift Service Mesh 3.0.17

Source published: Oct 8, 2026, 10:53:58 PM (timezone not stated)
Source modified: Oct 9, 2026, 3:54:59 PM (timezone not stated)
Observed here: 7 Nov 2026 12:37:26 UTC
Source terms: ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

nvd · CVE-2026-56866

Published

NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.

Source analysis status: Awaiting Analysis

Weakness classifications: CWE-444

Original publisher date fields

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

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

Source published: 8 Oct 2026 23:17:01 UTC
Source modified: 9 Oct 2026 16:35:35 UTC
Observed here: 25 Oct 2026 14:19:10 UTC
Source terms: NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 134c704f-9b21-4f2e-91b3-4a467353bcc0 · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

osv · GO-2026-6605

Published

Source published: 8 Oct 2026 22:31:09 UTC
Source modified: 16 Oct 2026 09:55:59 UTC
Observed here: 24 Oct 2026 13:19:41 UTC
Source terms: OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.