Everything has a vulnerability that Solarwinds hasn't disclosed. What is the logic in focusing on this extremely unique choice? A plan by a government wants to spearfish developers at every enterprise software company to find 1+ ways in to their clients and should have chosen something universal. Without any apparent data, it seems more likely the suspicion is just speculation because it is less common than email clients, legacy browsers, dev-servers, common libraries, etc.

I.e. because no one else found this intruder the crap software that everyone uses must be safe?

Yes, but that’s a big if. It’s also simply possible that Solarwinds has their TeamCity admin account password set to ‘password’ and accessible on a public network.

... actually, SolarWinds used "solarwinds123" on their FTP site.

Which is stored on a publicly-accessible GitHub repository.

(Source: https://www.theregister.com/2020/12/16/solarwinds_github_pas...)

Right, and we don't know, which means we should audit aggressively and assume these things may still be open attack vectors. You don't hang out with the backdoor open waiting for your friend to let you know.

I guess that's why they said that they are auditing aggressively their CI tool.

We should, but we should have assumed CI software was an attack vector since before the solar winds hack. It’s always been a vector. This hack doesn’t change anything.