A vulnerability exists in Rancher 2.1.4 in the login component, where the errorMsg
parameter can be tampered to display arbitrary content, filtering tags but not special characters or symbols. There’s no other limitation of the message, allowing malicious users to lure legitimate users to visit phishing sites with scare tactics, e.g., displaying a “This version of Rancher is outdated, please visit https://malicious.rancher.site/upgrading” message.
PoC
https://RANCHER:PORT/login?errorMsg=%68%74%74%70%73%3a%2f%2f%77%77%77%2e%6f%77%61%73%70%2e%6f%72%67%2f%69%6e%64%65%78%2e%70%68%70%2f%57%65%62%5f%50%61%72%61%6d%65%74%65%72%5f%54%61%6d%70%65%72%69%6e%67
It will display a link to OWASP Wiki explaining Web Parameter Tampering.