YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_APT_WEBSHELL_PHP_Sandworm_May20_1

Detects GIF header PHP webshell used by Sandworm on compromised machines

APT / threat actorSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X

Author: Florian Roth (Nextron Systems)
Date: 2020-05-28
Modified: 2023-12-05
Score / Quality: 75 / 85

What this rule detects

Detects GIF header PHP webshell used by Sandworm on compromised machines

It defines 2 patterns (2 text, 0 hex, 0 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

apt-webshell-php-sandworm-may20-1.yarDetection Rule License 1.1

rule SIGNATURE_BASE_APT_WEBSHELL_PHP_Sandworm_May20_1 : FILE
{
	meta:
		description = "Detects GIF header PHP webshell used by Sandworm on compromised machines"
		author = "Florian Roth (Nextron Systems)"
		id = "b9ec02c2-fa83-5f21-95cf-3528047b2d01"
		date = "2020-05-28"
		modified = "2023-12-05"
		reference = "https://media.defense.gov/2020/May/28/2002306626/-1/-1/0/CSA%20Sandworm%20Actors%20Exploiting%20Vulnerability%20in%20Exim%20Transfer%20Agent%2020200528.pdf"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_sandworm_exim_expl.yar#L86-L101"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "dc074464e50502459038ac127b50b8c68ed52817a61c2f97f0add33447c8f730"
		hash = "538d713cb47a6b5ec6a3416404e0fc1ebcbc219a127315529f519f936420c80e"
		logic_hash = "0d10f618c7b465c7691d6054e994a76f56c12eb0a36d2d98b5accd2c1e2c1da7"
		score = 75
		quality = 85
		tags = "FILE"

	strings:
		$h1 = "GIF89a <?php $" ascii
		$s1 = "str_replace(" ascii

	condition:
		filesize < 10KB and $h1 at 0 and $s1
}

Strings (2 patterns)

Identifier	Type	Value	Modifiers
$h1	text	"GIF89a <?php $"	ascii
$s1	text	"str_replace("	ascii

Condition

filesize < 10KB and $h1 at 0 and $s1

In plain words (Heuristic)

The file must be smaller than 10KB (a cheap guard that skips large files).
Pattern $h1 must be found at offset 0.
Pattern $s1 must be present.

Test this rule in your browser

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

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References

https://media.defense.gov/2020/May/28/2002306626/-1/-1/0/CSA%20Sandworm%20Actors%20Exploiting%20Vulnerability%20in%20Exim%20Transfer%20Agent%2020200528.pdf

Sample hashes

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

dc074464e50502459038ac127b50b8c68ed52817a61c2f97f0add33447c8f730
538d713cb47a6b5ec6a3416404e0fc1ebcbc219a127315529f519f936420c80e

Licence & attribution

Author: Florian Roth (Nextron Systems)

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: b9ec02c2-fa83-5f21-95cf-3528047b2d01

Tags:FILE

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