Unbounded range expansion in cron describe causes memory exhaustion in oban_web

Uncontrolled Resource Consumption vulnerability in oban-bg oban_web ('Elixir.Oban.Web.CronExpr' modules) allows memory exhaustion via unbounded cron range expansion.

An attacker with access to schedule cron jobs can submit a malicious cron expression such as "0 0 1-100000000 * *". When a user with dashboard access views the cron job list, 'Elixir.Oban.Web.CronExpr':describe/1 is called to render the expression. parse_range/1 parses both range endpoints via Integer.parse/1 with no bounds check, and the downstream helpers expand_dom_parts/1 and expand_dow_parts/1 materialise the range eagerly via Enum.to_list/1, causing allocation of ~2.4 GB and stalling or crashing the BEAM node. A sibling helper extract_dom_values already validates range bounds, but the expansion helpers do not.

This issue affects oban_web: from 2.12.0 before 2.12.5.

The vulnerability is exploitable when an attacker with access to schedule cron jobs submits a malicious cron expression. The crash is triggered when a user with dashboard access views the cron job list, which calls 'Elixir.Oban.Web.CronExpr':describe/1 to render the expression.