HTTP::Body versions before 1.23_01 for Perl allow CPU exhaustion via quadratic regex backtracking when parsing chunked request bodies. In chunked mode, used when no content length is given, add() matches each chunk-size line with `/^([\da-fA-F]+).*\x0D\x0A/`. On a line of hex digits whose first LF has no CR before it, the digits and `.*` backtrack against each other, so a single add() takes time quadratic in the line's length. Nothing limits how long the line can be. A remote attacker can exhaust CPU in applications that pass chunked request bodies to HTTP::Body.