CVE-2026-78663
The HTTP/2 server can refund connection-level flow control twice for the same data: Once when a…
- Risk score
- 69/100
- CVSS
- 9.1 v3.1
- Exploit chance (30 days)
- 0.6%
- Published
- 8 Oct 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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 …
- Affected
- See advisory
- Fix
- Apply the vendor's security update; see the linked advisory.
- Exploitation
- No known exploitation
Why it is Amber
- CVSS 9.1 critical
- Remotely exploitable without logging in
References
Original 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.
Last activity 8 Oct 2026. Patch Forecast updates every hour.