CVE-2026-78663

CVSS 9.1 (critical) · published 2026-10-08

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.

Weakness: CWE-675

Source: NVD CVE-2026-78663

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

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