When this crate is given a pathological certificate chain to validate, it will spend CPU time exponential with the number of candidate certificates at each step of path building.
Both TLS clients and TLS servers that accept client certificate are affected.
This was previously reported in https://github.com/briansmith/webpki/issues/69 and re-reported recently by Luke Malinowski.
webpki 0.22.1 included a partial fix and webpki 0.22.2 added further fixes.