CVE-2026-108525: HTTP/2 inbound flow control is not enforced, letting a client queue unbounded DATA in stream processes in Bandit

Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to exhaust server memory via DATA frames sent past the advertised receive window. The attacker requests a response larger than the 65,535-byte initial window and withholds WINDOWUPDATE, so the stream process blocks while sending and stops reading, then floods small DATA frames on that stream. Every frame is queued in the stream's mailbox until the BEAM node runs out of memory.

Bandit.HTTP2.Connection.handleframe/3 in lib/bandit/http2/connection.ex forwards each DATA frame to the stream process without consulting the receive window, and Bandit.HTTP2.FlowControl.computerecvwindow/2 replenishes the window as data arrives rather than as it is consumed, and never answers a violation with FLOWCONTROLERROR.

This issue affects bandit: from 0.3.1 before 1.14.0.