CVE-2026-78663
Double flow control refund on HTTP/2 server streams in net/http
Go standard library net/http
CVSS
9.1CriticalExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.57%Chance of exploitation activity in the next 30 days, higher than 46% of CVEs. Scored 23 Oct 2026FIRST EPSS
What fixes it
A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.
Description
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.
Text from CVE List
Affected versions 3
- net/httpaffected: all versions before 1.26.9CVE List
- net/http/internal/http2affected: 1.27.0-0 before 1.27.2CVE List
- golang.org/x/net/http2affected: all versions before 0.60.0CVE List
References 6
- go.dev/cl/847187Referencevia CVE List
- go.dev/cl/847310Referencevia CVE List
- go.dev/issue/81743Referencevia CVE List
- groups.google.com/g/golang-announce/c/U2fTuyDJznIReferencevia CVE List
- groups.google.com/g/golang-announce/c/ZPwCyRUuGBsReferencevia CVE List
- pkg.go.dev/vuln/GO-2026-6612Referencevia CVE List