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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_ASPX_Sharepoint_Drop_CVE_2025_53770_Jul25

Detects ASPX web shell dropped during the exploitation of SharePoint RCE vulnerability CVE-2025-53770

WebshellSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X
Author
Florian Roth
Date
2025-07-20
Modified
2026-05-15
Score / Quality
80 / 85

What this rule detects

Detects ASPX web shell dropped during the exploitation of SharePoint RCE vulnerability CVE-2025-53770

It defines 3 patterns (3 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
webshell-aspx-sharepoint-drop-cve-2025-53770-jul25.yarDetection Rule License 1.1
rule SIGNATURE_BASE_WEBSHELL_ASPX_Sharepoint_Drop_CVE_2025_53770_Jul25 : CVE_2025_53770 FILE
{
	meta:
		description = "Detects ASPX web shell dropped during the exploitation of SharePoint RCE vulnerability CVE-2025-53770"
		author = "Florian Roth"
		id = "f1c8f671-a0d2-5aaf-93f4-025dace0dbe1"
		date = "2025-07-20"
		modified = "2026-05-15"
		reference = "https://research.eye.security/sharepoint-under-siege/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/expl_sharepoint_jul25.yar#L1-L21"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "27c45b8ed7b8a7e5fff473b50c24028bd028a9fe8e25e5cea2bf5e676e531014"
		hash = "92bb4ddb98eeaf11fc15bb32e71d0a63256a0ed826a03ba293ce3a8bf057a514"
		hash = "b336f936be13b3d01a8544ea3906193608022b40c28dd8f1f281e361c9b64e93"
		logic_hash = "3c7bb848fc73418d5a3ecae6e9f637a7d07bf45a75b1bd0a278fdbfae428d619"
		score = 80
		quality = 85
		tags = "CVE-2025-53770, FILE"

	strings:
		$x1 = "var sy = System.Reflection.Assembly.Load(" ascii
		$x2 = "Response.Write(cg.ValidationKey+" ascii
		$s1 = "<script runat=\"server\" language=\"c#\" CODEPAGE=\"65001\">" ascii fullword

	condition:
		filesize < 4KB and 1 of ( $x* ) or all of them
}

Strings (3 patterns)

IdentifierTypeValueModifiers
$x1text"var sy = System.Reflection.Assembly.Load("ascii
$x2text"Response.Write(cg.ValidationKey+"ascii
$s1text"<script runat=\"server\" language=\"c#\" CODEPAGE=\"65001\">"ascii fullword

Condition

filesize < 4KB and 1 of ( $x* ) or all of them

In plain words (Heuristic)

  • The file must be smaller than 4KB (a cheap guard that skips large files).
  • All patterns in the rule must match.
  • At least 1 patterns in ( $x* ) must match.

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Drop a file here or click to chooseScanned locally with YARA-X. Files up to 200 MB.

Open in editor

References

Sample hashes

Hashes of samples the author lists in the rule's meta (look them up in your threat-intelligence platform).

  • 27c45b8ed7b8a7e5fff473b50c24028bd028a9fe8e25e5cea2bf5e676e531014
  • 92bb4ddb98eeaf11fc15bb32e71d0a63256a0ed826a03ba293ce3a8bf057a514
  • b336f936be13b3d01a8544ea3906193608022b40c28dd8f1f281e361c9b64e93

Licence & attribution

Author: Florian Roth

Source repository: Signature Base (Florian Roth / Nextron) @ 94a1c48d7a

Licence: Detection Rule License 1.1 (repository licence)

Original rule

Mirrored via YARA Forge 20260927, which prefixes rule names with the source and adds normalised meta fields.

Rule id: f1c8f671-a0d2-5aaf-93f4-025dace0dbe1

Tags:CVE_2025_53770FILE

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