WEBSHELL_ASPX_SimpleSeeSharp

YARA detection rule by threatintel@volexity.com · NOASSERTION

A simple ASPX Webshell that allows an attacker to write further files to disk.

rule WEBSHELL_ASPX_SimpleSeeSharp : Webshell Unclassified {
   meta:
      author = "threatintel@volexity.com"
      date = "2021-03-01"
      description = "A simple ASPX Webshell that allows an attacker to write further files to disk."
      hash = "893cd3583b49cb706b3e55ecb2ed0757b977a21f5c72e041392d1256f31166e2"
      reference = "https://www.volexity.com/blog/2021/03/02/active-exploitation-of-microsoft-exchange-zero-day-vulnerabilities/"
      id = "469fdf5c-e09e-5d44-a2e6-0864dcd0e18a"
   strings:
      $header = "<%@ Page Language=\"C#\" %>"
      $body = "<% HttpPostedFile thisFile = Request.Files[0];thisFile.SaveAs(Path.Combine"
   condition:
      $header at 0 and
      $body and
      filesize < 1KB
}

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

64da3d56-5668-4341-8b99-ffed22577117

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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