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Microsoft on Friday disclosed it has made more improvements to the mitigation method offered as a means to prevent exploitation attempts against the newly disclosed unpatched security flaws in Exchange Server.

To that end, the tech giant has revised the blocking rule in IIS Manager from “.*autodiscover\.json.*Powershell.*” to “(?=.*autodiscover\.json)(?=.*powershell).”

The list of updated steps to add the URL Rewrite rule is below –

  • Open IIS Manager
  • Select Default Web Site
  • In the Feature View, click URL Rewrite
  • In the Actions pane on the right-hand side, click Add Rule(s)…
  • Select Request Blocking and click OK
  • Add the string “(?=.*autodiscover\.json)(?=.*powershell)” (excluding quotes)
  • Select Regular Expression under Using
  • Select Abort Request under How to block and then click OK
  • Expand the rule and select the rule with the pattern: (?=.*autodiscover\.json)(?=.*powershell) and click Edit under Conditions
  • Change the Condition input from {URL} to {UrlDecode:{REQUEST_URI}} and then click OK

images from Hacker News