YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_WEBSHELL_ASPX_Compiled_Sharepoint_Drop_CVE_2025_53770_Jul25_2

Detects compiled 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, Marius Benthin
Date: 2025-07-20
Modified: 2025-07-25
Score / Quality: 75 / 83

What this rule detects

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

Targets: Windows PE.

It defines 7 patterns (3 text, 0 hex, 4 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

webshell-aspx-compiled-sharepoint-drop-cve-2025-53770-jul25-2.yarDetection Rule License 1.1

rule SIGNATURE_BASE_WEBSHELL_ASPX_Compiled_Sharepoint_Drop_CVE_2025_53770_Jul25_2 : CVE_2025_53770 FILE
{
	meta:
		description = "Detects compiled ASPX web shell dropped during the exploitation of SharePoint RCE vulnerability CVE-2025-53770"
		author = "Florian Roth, Marius Benthin"
		id = "00a844ab-aede-53bf-820f-d43a5d96426d"
		date = "2025-07-20"
		modified = "2025-07-25"
		reference = "https://research.eye.security/sharepoint-under-siege/"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/expl_sharepoint_jul25.yar#L23-L53"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "8d3d3f3a17d233bc8562765e61f7314ca7a08130ac0fb153ffd091612920b0f2"
		hash = "d8ca5e5d6400ac34ac4cc138efa89d2ec4d5c0e968a78fa3ba5dbc04c7550649"
		hash = "7e9b77da1f51d03ee2f96bc976f6aeb781f801cf633862a4b8c356cbb555927d"
		logic_hash = "df11e5bd293cf094f3a147b54ecaafbe0804d7d575fcc22f38e77ab155c7ebdc"
		score = 75
		quality = 83
		tags = "CVE-2025-53770, FILE"

	strings:
		$x1 = /App_Web_spinstall\d{0,1}.aspx/ wide
		$x2 = /spinstall[\w]?[\._]aspx/ ascii
		$x3 = /\/_layouts\/1[0-9]\/spinstall/ wide
		$x4 = /\/_layouts\/1[0-9]\/ghostfile/ wide
		$s1 = "System.Web.Configuration.MachineKeySection" wide
		$s2 = "Page_load" ascii fullword
		$s3 = "GetApplicationConfig" wide fullword

	condition:
		uint16( 0 ) == 0x5a4d and filesize < 20KB and ( 1 of ( $x* ) or all of ( $s* ) ) or 2 of ( $x* ) or 4 of them
}

Strings (7 patterns)

Identifier	Type	Value	Modifiers
$x1	regex	/App_Web_spinstall\d{0,1}.aspx/	wide
$x2	regex	/spinstall[\w]?[\._]aspx/	ascii
$x3	regex	/\/_layouts\/1[0-9]\/spinstall/	wide
$x4	regex	/\/_layouts\/1[0-9]\/ghostfile/	wide
$s1	text	"System.Web.Configuration.MachineKeySection"	wide
$s2	text	"Page_load"	ascii fullword
$s3	text	"GetApplicationConfig"	wide fullword

Condition

uint16( 0 ) == 0x5a4d and filesize < 20KB and ( 1 of ( $x* ) or all of ( $s* ) ) or 2 of ( $x* ) or 4 of them

In plain words (Heuristic)

The file must start with “MZ” — a Windows executable (PE).
The file must be smaller than 20KB (a cheap guard that skips large files).
All patterns in ( $s* ) must match.
At least 1 patterns in ( $x* ) must match.
At least 2 patterns in ( $x* ) must match.
At least 4 patterns in the rule must match.

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References

https://research.eye.security/sharepoint-under-siege/

Sample hashes

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

8d3d3f3a17d233bc8562765e61f7314ca7a08130ac0fb153ffd091612920b0f2
d8ca5e5d6400ac34ac4cc138efa89d2ec4d5c0e968a78fa3ba5dbc04c7550649
7e9b77da1f51d03ee2f96bc976f6aeb781f801cf633862a4b8c356cbb555927d

Licence & attribution

Author: Florian Roth, Marius Benthin

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: 00a844ab-aede-53bf-820f-d43a5d96426d

Tags:CVE_2025_53770 FILE

SIGNATURE_BASE_WEBSHELL_ASPX_Sharepoint_Drop_CVE_2025_53770_Jul25
WebshellSignature Base (Florian Roth / Nextron)· Florian Roth· 2025-07-20