CVE-2026-85062: Colord: Slow rejection of oversized malformed color strings

colord’s CSS color string matchers described a number as ([+-]?\d*\.?\d+). In that form \d* and \d+ can match the same digits, so a run of n digits can be divided between them in O(n²) ways, and rejecting an input retries every division. Parsing is synchronous and uninterruptible, so a long malformed color string blocks the thread:

Reachable through colord() and getFormat(), and through any method that accepts a color string — including isEqual(), mix() and contrast(). The affected matchers are parseRgbaString and parseHslaString (built in) and parseHwbaString, parseLchaString, parseCmykaString (plugins).

Growth is polynomial, not exponential — multi-kilobyte payloads are required for a noticeable stall.