CVE-2026-100350: kin-openapi deepObject query decoding repeatedly compiles an invariant regular expression

openapi3filter decodes deepObject-style query parameters by looping over every key in the request’s query string. Inside that loop it recompiles a loop-invariant regular expression on every iteration. The pattern depends only on the spec-defined parameter name, not on the loop variable, so it is compiled N times for N query keys instead of once. Because the number of query keys is attacker-controlled and unbounded, a single request with many junk query keys forces a proportional number of regexp.MustCompile calls, consuming CPU. A handful of concurrent requests can saturate all cores — an uncontrolled-resource-consumption denial of service.

This is not ReDoS: the pattern is fixed (^<param>\[) and matches in linear time. The cost is the repeated compilation of an invariant regexp, once per attacker-supplied query key.