YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_FE_APT_Webshell_PL_PULSECHECK_1

Detects samples mentioned in PulseSecure report

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

Author: Mandiant
Date: 2021-04-16
Modified: 2023-12-05
Score / Quality: 75 / 85

What this rule detects

Detects samples mentioned in PulseSecure report

It defines 8 patterns (7 text, 0 hex, 1 regex).

Summary generated from the rule's metadata and condition.

Rule source

Download .yar

fe-apt-webshell-pl-pulsecheck-1.yarDetection Rule License 1.1

rule SIGNATURE_BASE_FE_APT_Webshell_PL_PULSECHECK_1
{
	meta:
		description = "Detects samples mentioned in PulseSecure report"
		author = "Mandiant"
		id = "f375fdd8-567b-569b-85f4-af54a35d2a93"
		date = "2021-04-16"
		modified = "2023-12-05"
		reference = "https://www.fireeye.com/blog/threat-research/2021/04/suspected-apt-actors-leverage-bypass-techniques-pulse-secure-zero-day.html"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/apt_pulsesecure.yar#L116-L136"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		hash = "a1dcdf62aafc36dd8cf64774dea80d79fb4e24ba2a82adf4d944d9186acd1cc1"
		logic_hash = "aba457dd33232ef37ca145c5b7cd9c5fe809730339a55c5e90ac46b4a136f6cb"
		score = 75
		quality = 85
		tags = ""

	strings:
		$r1 = /while[\x09\x20]{0,32}\(<\w{1,64}>\)[\x09\x20]{0,32}\{\s{1,256}\$\w{1,64}[\x09\x20]{0,32}\.=[\x09\x20]{0,32}\$_;\s{0,256}\}/
		$s1 = "use Crypt::RC4;"
		$s2 = "use MIME::Base64"
		$s3 = "MIME::Base64::decode("
		$s4 = "popen("
		$s5 = " .= $_;"
		$s6 = "print MIME::Base64::encode(RC4("
		$s7 = "HTTP_X_"

	condition:
		$s1 and $s2 and ( @s3 [ 1 ] < @s4 [ 1 ] ) and ( @s4 [ 1 ] < @s5 [ 1 ] ) and ( @s5 [ 1 ] < @s6 [ 1 ] ) and ( #s7 > 2 ) and $r1
}

Strings (8 patterns)

Identifier	Type	Value
$r1	regex	/while[\x09\x20]{0,32}$<\w{1,64}>$[\x09\x20]{0,32}\{\s{1,256}\$\w{1,64}[\x09\x20]{0,32}\.=[\x09\x20]{0,32}\$_;\s{0,256}\}/
$s1	text	"use Crypt::RC4;"
$s2	text	"use MIME::Base64"
$s3	text	"MIME::Base64::decode("
$s4	text	"popen("
$s5	text	" .= $_;"
$s6	text	"print MIME::Base64::encode(RC4("
$s7	text	"HTTP_X_"

Condition

$s1 and $s2 and ( @s3 [ 1 ] < @s4 [ 1 ] ) and ( @s4 [ 1 ] < @s5 [ 1 ] ) and ( @s5 [ 1 ] < @s6 [ 1 ] ) and ( #s7 > 2 ) and $r1

In plain words (Heuristic)

Pattern $s7 must occur > 2 times.
Pattern $s1 must be present.
Pattern $s2 must be present.
Pattern $r1 must be present.

Test this rule in your browser

Drop a file to scan it with this rule using YARA-X compiled to WebAssembly. Nothing is uploaded.

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

Open in editor

References

https://www.fireeye.com/blog/threat-research/2021/04/suspected-apt-actors-leverage-bypass-techniques-pulse-secure-zero-day.html

Sample hashes

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

a1dcdf62aafc36dd8cf64774dea80d79fb4e24ba2a82adf4d944d9186acd1cc1

Licence & attribution

Author: Mandiant

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: f375fdd8-567b-569b-85f4-af54a35d2a93

SIGNATURE_BASE_M_APT_Downloader_BEATDROP
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2022-04-28
SIGNATURE_BASE_APT_NK_MAL_M_Hunting_VEILEDSIGNAL_1
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2023-04-20
SIGNATURE_BASE_APT_NK_MAL_M_Hunting_VEILEDSIGNAL_2
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2023-04-20
SIGNATURE_BASE_APT_NK_MAL_M_Hunting_VEILEDSIGNAL_3
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2023-04-20
SIGNATURE_BASE_APT_NK_MAL_M_Hunting_VEILEDSIGNAL_4
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2023-04-20
SIGNATURE_BASE_APT_NK_MAL_M_Hunting_VEILEDSIGNAL_5
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2023-04-20
SIGNATURE_BASE_APT_NK_MAL_M_Hunting_VEILEDSIGNAL_6
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2023-04-20
SIGNATURE_BASE_APT_UNC4736_NK_MAL_TAXHAUL_3CX_Apr23_1
APT / threat actorSignature Base (Florian Roth / Nextron)· Mandiant· 2023-03-04

Identifier	Type	Value
$r1	regex	/while[\x09\x20]{0,32}\(<\w{1,64}>\)[\x09\x20]{0,32}\{\s{1,256}\$\w{1,64}[\x09\x20]{0,32}\.=[\x09\x20]{0,32}\$_;\s{0,256}\}/
$s1	text	"use Crypt::RC4;"
$s2	text	"use MIME::Base64"
$s3	text	"MIME::Base64::decode("
$s4	text	"popen("
$s5	text	" .= $_;"
$s6	text	"print MIME::Base64::encode(RC4("
$s7	text	"HTTP_X_"