Updated LinkedIn's country subdomain SSL certificate has expired – apparently as of about noon GMT today.
According to the
sslscan certificate testing tool, us.linkedin.com and all its altnames were no longer valid at the time of publication.
The certificate issuer is DigiCert SHA2 Secure Server CA.
The certificate for the naked domain, www.linkedin.com, is separate – and still kosher until noon GMT on December 14 next year.
Kami Vaniea, a cybersecurity and privacy researcher at the University of Edinburgh, told The Register: "They shouldn't have let it happen."
She said "a large percentage" of web users visiting a site they have been to before, especially a trusted site, will "click through" certificate warnings.
She said having an invalid certificate warning "trains users that it's safe to click through those warnings" and "the next one might be a real attack".
Security researcher Scott Helme pointed out that LinkedIn uses HSTS secure headers, so if you're using a browser supporting it (he said "most modern browsers" do) then it won't let you click through if you've visited before, which helps a lot (the visit would be stored in cache). "Without HSTS many users could have clicked through the error message that most browsers offer and bypassed the security warning. That would have allowed them to browse the site with broken HTTPS which is highly dangerous," he said.
"If the certificate is invalid then we have no assurance that our communications are secure. We should think of HTTPS with an invalid certificate as the same as using HTTP, anyone could see or tamper with what we're doing online." However, us.linkedin.com does not use HSTS pre-loading, meaning that users who are visiting the site for the first time would still be able to click through – even with HSTS.
Alan Woodward, a security researcher at the University of Surrey, told The Reg: "Simply put, it will erode trust with visitors to your site.
"For a site like LinkedIn that could matter a great deal when people come to trust them with more data, something LinkedIn is always encouraging you to do to – 'complete your profile'.
"It's not the first big name to forget to renew certificates, and it is easy to forget sub domains, but really with the reminders that the CA sends, it’s surprising it still happens."
Helme told The Register: "This is a good indicator that they may still be renewing and replacing these certificates manually and not using an automated process."
"It's not very hard to reissue the certificate," Vaniea added. So you would expect that Microsoft would resolve the issue quickly. However, the certificate first needs to be signed by the issuing authority (DigiCert) and the changes then take some time to propagate out to everyone.
In the meantime, maybe we can go back to networking in the real world?
Here's a full list of the us.linkedin.com altnames, if you're curious:
Altnames: DNS:us.linkedin.com, DNS:ae.linkedin.com, DNS:ar.linkedin.com, DNS:au.linkedin.com, DNS:be.linkedin.com, DNS:br.linkedin.com, DNS:ca.linkedin.com, DNS:ch.linkedin.com, DNS:cl.linkedin.com, DNS:cn.linkedin.com, DNS:co.linkedin.com, DNS:cz.linkedin.com, DNS:de.linkedin.com, DNS:dk.linkedin.com, DNS:es.linkedin.com, DNS:fi.linkedin.com, DNS:fr.linkedin.com, DNS:gr.linkedin.com, DNS:hk.linkedin.com, DNS:id.linkedin.com, DNS:ie.linkedin.com, DNS:il.linkedin.com, DNS:in.linkedin.com, DNS:ir.linkedin.com, DNS:it.linkedin.com, DNS:jp.linkedin.com, DNS:me.linkedin.com, DNS:mx.linkedin.com, DNS:my.linkedin.com, DNS:nl.linkedin.com, DNS:no.linkedin.com, DNS:nz.linkedin.com, DNS:ph.linkedin.com, DNS:pk.linkedin.com, DNS:pl.linkedin.com, DNS:pt.linkedin.com, DNS:qa.linkedin.com, DNS:ro.linkedin.com, DNS:rs.linkedin.com, DNS:ru.linkedin.com, DNS:se.linkedin.com, DNS:sg.linkedin.com, DNS:tr.linkedin.com, DNS:uk.linkedin.com, DNS:za.linkedin.com, DNS:af.linkedin.com, DNS:al.linkedin.com, DNS:at.linkedin.com, DNS:ba.linkedin.com, DNS:bd.linkedin.com, DNS:bg.linkedin.com, DNS:bh.linkedin.com, DNS:bo.linkedin.com, DNS:cr.linkedin.com, DNS:cy.linkedin.com, DNS:do.linkedin.com, DNS:dz.linkedin.com, DNS:ec.linkedin.com, DNS:ee.linkedin.com, DNS:eg.linkedin.com, DNS:gh.linkedin.com, DNS:gt.linkedin.com, DNS:hr.linkedin.com, DNS:hu.linkedin.com, DNS:is.linkedin.com, DNS:jm.linkedin.com, DNS:jo.linkedin.com, DNS:ke.linkedin.com, DNS:kr.linkedin.com, DNS:kw.linkedin.com, DNS:kz.linkedin.com, DNS:lb.linkedin.com, DNS:lk.linkedin.com, DNS:lt.linkedin.com, DNS:lu.linkedin.com, DNS:lv.linkedin.com, DNS:ma.linkedin.com, DNS:mk.linkedin.com, DNS:mt.linkedin.com, DNS:mu.linkedin.com, DNS:ng.linkedin.com, DNS:np.linkedin.com, DNS:om.linkedin.com, DNS:pa.linkedin.com, DNS:pe.linkedin.com, DNS:pr.linkedin.com, DNS:sa.linkedin.com, DNS:si.linkedin.com, DNS:sk.linkedin.com, DNS:sv.linkedin.com, DNS:th.linkedin.com, DNS:tn.linkedin.com, DNS:tt.linkedin.com, DNS:tw.linkedin.com, DNS:tz.linkedin.com, DNS:ua.linkedin.com, DNS:ug.linkedin.com, DNS:uy.linkedin.com, DNS:ve.linkedin.com, DNS:vn.linkedin.com, DNS:zw.linkedin.com, DNS:la.linkedin.com, DNS:bm.linkedin.com, DNS:iq.linkedin.com, DNS:ly.linkedin.com, DNS:sd.linkedin.com, DNS:sy.linkedin.com, DNS:ye.linkedin.com, DNS:ci.linkedin.com, DNS:tg.linkedin.com
We've not heard back from Microsoft, which swallowed the biz networking biz for a cool $26bn back in June last year, but LinkedIn Help recently tweeted:
Some members may be experiencing issues with our site. Our team is working hard to resolve. Stay tuned.— LinkedIn Help (@LinkedInHelp) November 30, 2017
Updated at 16.25 to add: New certs appear to have hastily deployed. Green padlocks all round to our dev chums.