CVE-2026-54297: Faraday: Uncontrolled recursion in NestedParamsEncoder allows stack exhaustion DoS via deeply nested query parameters

Faraday::NestedParamsEncoder, the default nested query parameter encoder/decoder in Faraday, decodes nested query strings without enforcing a maximum nesting depth.

A crafted query string such as:

a[x][x][x][x]...[x]=1

causes Faraday to build a deeply nested Ruby Hash structure. The internal dehash routine then recursively walks this attacker-controlled structure without a depth limit. At sufficient depth, Ruby raises an uncaught SystemStackError (stack level too deep), crashing the calling thread or worker.

This can lead to denial of service in applications that pass attacker-controlled query strings to Faraday’s nested query parsing or URL-building paths.