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YARA · Signature Base (Florian Roth / Nextron)

SIGNATURE_BASE_LOG_EXPL_Proxytoken_Exploitation_Aug21_1

Detects ProxyToken CVE-2021-33766 exploitation attempts on an unpatched system

ExploitSignature Base (Florian Roth / Nextron)Detection Rule License 1.1Compiles with YARA-X (with warnings)
Author
Florian Roth (Nextron Systems)
Date
2021-08-30
Modified
2023-12-05
Score / Quality
75 / 85

What this rule detects

Detects ProxyToken CVE-2021-33766 exploitation attempts on an unpatched system

It defines 6 patterns (6 text, 0 hex, 0 regex).

YARA-X says: warning[duplicate_pattern_value]: duplicate pattern value

Summary generated from the rule's metadata and condition.

Rule source

Download .yar
log-expl-proxytoken-exploitation-aug21-1.yarDetection Rule License 1.1
rule SIGNATURE_BASE_LOG_EXPL_Proxytoken_Exploitation_Aug21_1 : CVE_2021_33766
{
	meta:
		description = "Detects ProxyToken CVE-2021-33766 exploitation attempts on an unpatched system"
		author = "Florian Roth (Nextron Systems)"
		id = "f4840140-6d31-52f9-b1a0-2acdd4b955cd"
		date = "2021-08-30"
		modified = "2023-12-05"
		reference = "https://www.zerodayinitiative.com/blog/2021/8/30/proxytoken-an-authentication-bypass-in-microsoft-exchange-server"
		source_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/yara/exploit_cve_2021_33766_proxytoken.yar#L2-L21"
		license_url = "https://github.com/Neo23x0/signature-base/blob/94a1c48d7ab499879287ff611dfe7f9c56376030/LICENSE"
		logic_hash = "ff0c3e4f7491f5faec3e2688819ea5ec636a7d4eb57941afff6f53f60b0c0293"
		score = 75
		quality = 85
		tags = "CVE-2021-33766"

	strings:
		$ss0 = "POST " ascii
		$ss1 = " 500 0 0"
		$sa1 = "/ecp/" ascii
		$sa2 = "/RulesEditor/InboxRules.svc/NewObject" ascii
		$sb1 = "/ecp/" ascii
		$sb2 = "SecurityToken=" ascii

	condition:
		all of ( $ss* ) and ( all of ( $sa* ) or all of ( $sb* ) )
}

Strings (6 patterns)

IdentifierTypeValueModifiers
$ss0text"POST "ascii
$ss1text" 500 0 0"
$sa1text"/ecp/"ascii
$sa2text"/RulesEditor/InboxRules.svc/NewObject"ascii
$sb1text"/ecp/"ascii
$sb2text"SecurityToken="ascii

Condition

all of ( $ss* ) and ( all of ( $sa* ) or all of ( $sb* ) )

In plain words (Heuristic)

  • All patterns in ( $ss* ) must match.
  • All patterns in ( $sa* ) must match.
  • All patterns in ( $sb* ) must match.

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References

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: f4840140-6d31-52f9-b1a0-2acdd4b955cd

Tags:CVE_2021_33766

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