Critical 9.1Published Oct 8, 2026

CVE-2026-78663Double flow control refund on HTTP/2 server streams in net/http

Updated under an hour ago (2026-10-19 08:20 UTC)

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It affects Go standard library net/http and 2 other products. Add what you run to find out whether that includes you.

EPSS puts the chance of exploitation in the next 30 days at 0.57%, higher than 46% of scored CVEs.

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Every CVE for Go standard library net/http

Exploited in the last 30 days

The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a client resets a stream (refunding data for any sent-but-unread portion of the stream), and again when a request handler reads the buffered data. A malicious client can exploit this to bypass the configured connection-level flow control limit (MaxReceiveBufferPerConnection). Total buffered data is still limited by the concurrent stream limit and stream-level flow control.

CVSS: 9.1 CRITICAL (v3.1, CISA ADP)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Weakness (CWE): CWE-675
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 0.57% (percentile 46)
Assigned by: Go
NVD analysis: Awaiting Analysis
Record last updated: Oct 9, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Go standard library net/http go_standard_library:net_http (from the name)	before 1.26.9	CNA record
Go standard library net/http/internal/http2 go_standard_library:net_http_internal_http2 (from the name)	from 1.27.0-0 before 1.27.2	CNA record
golang.org/x/net golang.org/x/net/http2 golang.org_x_net:http2 (from the name)	before 0.60.0	CNA record

References

https://go.dev/cl/847187
https://go.dev/cl/847310
https://go.dev/issue/81743
https://groups.google.com/g/golang-announce/c/U2fTuyDJznI
https://groups.google.com/g/golang-announce/c/ZPwCyRUuGBs
https://pkg.go.dev/vuln/GO-2026-6612

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.