CVE-2026-110499: Client-chosen HPACK encoder table size is applied uncapped, growing per-connection state with every response in Bandit

Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 implementation of mtrudel bandit allows an unauthenticated remote attacker to grow per-connection memory and CPU cost without bound via a large SETTINGSHEADERTABLESIZE. Bandit resizes its HPACK encoder table to whatever size the client advertises, up to 2^32-1 bytes, and indexes response headers into it. Because responses carry distinct values such as date or content-length, nothing is evicted and the table grows with every response for the life of the connection, while each lookup scans it linearly.

The SETTINGS handling in Bandit.HTTP2.Connection (lib/bandit/http2/connection.ex) passes remotesettings.headertablesize to HPAX.resize/2 with no server-side cap, and encodeheaders encodes every response header as :store. Serving N responses on one connection therefore costs O(N²) CPU in the connection process.

This issue affects bandit: from 0.3.6 before 1.14.0.