Memory exhaustion via unbounded deserialization of keyset pagination cursors in Ash.Page.Keyset

Uncontrolled Resource Consumption vulnerability in ash-project ash allows an attacker to exhaust the memory of the node via a crafted keyset pagination cursor.

Read actions with keyset pagination deserialize the client-supplied page[:after] or page[:before] cursor in decode_values/2 in lib/ash/page/keyset.ex, which base64-decodes the value and passes it to :erlang.binary_to_term/2 without bounding its size. The Erlang external term format supports zlib-compressed payloads, which the decoder inflates transparently, so a cursor of a few kilobytes can allocate tens of megabytes of heap in a single call. Ash itself only ever encodes cursors uncompressed, so the decoder accepts a term shape its encoder never produces. Concurrent requests aggregate these allocations and can terminate the node.

This issue affects ash: from 1.17.0 before 3.31.1.

A read action must declare keyset? true in its pagination block, and the application must pass a client-supplied value as the :after or :before page option.