S0661: FoggyWeb

FoggyWeb is a passive and highly-targeted backdoor capable of remotely exfiltrating sensitive information from a compromised Active Directory Federated Services (AD FS) server. It has been used by APT29 since at least early April 2021.[1]

EnterpriseS0661MalwareObject v1.1ModifiedApr 11, 2024, 02:32 UTC (UTC+00:00)

S0661: FoggyWeb describes [FoggyWeb](https://attack.mitre.org/software/S0661) is a passive and highly-targeted backdoor capable of remotely exfiltrating sensitive information from a compromised Active Directory Federated Services (AD FS) server. It has been used by [APT29](https://attack.mitre.org/groups/G0016) since at least early April 2021.(Citation: MSTIC FoggyWeb September 2021)

Executive priority

S0661: FoggyWeb is an official MITRE ATT&CK software. Glexia treats it as defensive behavior context for prioritizing monitoring, control validation, and response planning without using the object by itself as an attribution claim.

Technical view

Security teams should validate S0661: FoggyWeb by reviewing the official ATT&CK relationships, mapped tactics (the mapped ATT&CK tactic context), supported platforms (Windows), and available local telemetry before making detection or mitigation decisions.

Likely telemetry

Official ATT&CK relationships and object metadata
Network, endpoint, and security-tool telemetry

Detection direction

Validate whether S0661: FoggyWeb appears in your detection coverage and tabletop scenarios.
Use the object to align executive risk language with SOC, incident response, and detection engineering work.
Do not treat ATT&CK relationship context as attribution without corroborating evidence.

Mitigation priorities

Map the object to existing controls and identify missing telemetry or response ownership.
Prioritize mitigations that reduce exposure on the listed platforms and tactics.
Review adjacent ATT&CK relationships before changing policy, detections, or reporting language.

Additional notes and limits

Baseline Glexia take generated from the official MITRE ATT&CK STIX object, source hash, tactics, platforms, and detection fields. It is safe to replace with a richer model-generated take for the same source hash later.

This baseline take is source-grounded and schema-validated, but it does not include environment-specific telemetry, incident evidence, or threat-intelligence corroboration.

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Official MITRE ATT&CK definition

FoggyWeb

View the same entry on attack.mitre.org (MITRE-hosted reference; in-page links above use the Glexia ATT&CK library.)

Glexia analysis

How security teams should use this page

Treat this object as behavior context, not an attribution claim. Validate the related groups, software, data sources, and mitigations against official ATT&CK relationships and your own telemetry before making control-coverage decisions.

ATT&CK relationship table

Techniques used

This mirrors the MITRE pattern of making group, software, campaign, and technique relationships scannable. Relationship notes come from mirrored ATT&CK relationship text when available.

Filter related techniques21 rows

Domain	ID	Name	Relationship / procedure
Enterprise	T1140	Deobfuscate/Decode Files or Information	FoggyWeb can be decrypted in memory using a Lightweight Encryption Algorithm (LEA)-128 key and decoded using a XOR key.[1]
Enterprise	T1560.003	Archive via Custom MethodSub-technique	FoggyWeb can use a dynamic XOR key and a custom XOR methodology to encode data before exfiltration. Also, FoggyWeb can encode C2 command output within a legitimate WebP file.[1]
Enterprise	T1041	Exfiltration Over C2 Channel	FoggyWeb can remotely exfiltrate sensitive information from a compromised AD FS server.[1]
Enterprise	T1027.004	Compile After DeliverySub-technique	FoggyWeb can compile and execute source code sent to the compromised AD FS server via a specific HTTP POST.[1]
Enterprise	T1005	Data from Local System	FoggyWeb can retrieve configuration data from a compromised AD FS server.[1]
Enterprise	T1027.013	Encrypted/Encoded FileSub-technique	FoggyWeb has been XOR-encoded.[1]
Enterprise	T1071.001	Web ProtocolsSub-technique	FoggyWeb has the ability to communicate with C2 servers over HTTP GET/POST requests.[1]
Enterprise	T1552.004	Private KeysSub-technique	FoggyWeb can retrieve token signing certificates and token decryption certificates from a compromised AD FS server.[1]
Enterprise	T1036	Masquerading	FoggyWeb can masquerade the output of C2 commands as a fake, but legitimately formatted WebP file.[1]
Enterprise	T1057	Process Discovery	FoggyWeb's loader can enumerate all Common Language Runtimes (CLRs) and running Application Domains in the compromised AD FS server's `Microsoft.IdentityServer.ServiceHost.exe` process.[1]
Enterprise	T1550	Use Alternate Authentication Material	FoggyWeb can allow abuse of a compromised AD FS server's SAML token.[1]
Enterprise	T1106	Native API	FoggyWeb's loader can use API functions to load the FoggyWeb backdoor into the same Application Domain within which the legitimate AD FS managed code is executed.[1]
Enterprise	T1129	Shared Modules	FoggyWeb's loader can call the `load()` function to load the FoggyWeb dll into an Application Domain on a compromised AD FS server.[1]
Enterprise	T1040	Network Sniffing	FoggyWeb can configure custom listeners to passively monitor all incoming HTTP GET and POST requests sent to the AD FS server from the intranet/internet and intercept HTTP requests that match the custom URI patterns defined by the actor.[1]
Enterprise	T1560.002	Archive via LibrarySub-technique	FoggyWeb can invoke the `Common.Compress` method to compress data with the C# GZipStream compression class.[1]
Enterprise	T1105	Ingress Tool Transfer	FoggyWeb can receive additional malicious components from an actor controlled C2 server and execute them on a compromised AD FS server.[1]
Enterprise	T1574.001	DLLSub-technique	FoggyWeb's loader has used DLL Search Order Hijacking to load malicious code instead of the legitimate `version.dll` during the `Microsoft.IdentityServer.ServiceHost.exe` execution process.[1]
Enterprise	T1036.005	Match Legitimate Resource Name or LocationSub-technique	FoggyWeb can be disguised as a Visual Studio file such as `Windows.Data.TimeZones.zh-PH.pri` to evade detection. Also, FoggyWeb's loader can mimic a genuine `dll` file that carries out the same import functions as the legitimate Windows `version.dll` file.[1]
Enterprise	T1083	File and Directory Discovery	FoggyWeb's loader can check for the FoggyWeb backdoor .pri file on a compromised AD FS server.[1]
Enterprise	T1620	Reflective Code Loading	FoggyWeb's loader has reflectively loaded .NET-based assembly/payloads into memory.[1]
Enterprise	T1573.001	Symmetric CryptographySub-technique	FoggyWeb has used a dynamic XOR key and custom XOR methodology for C2 communications.[1]

Associated objects

Groups, software, and campaigns

G0016: APT29

APT29 is threat group that has been attributed to Russia's Foreign Intelligence Service (SVR).[1][2] They have operated since at least 2008, often targeting government networks in Europe and NATO member countries, research institutes, and think tanks. APT29 reportedly compromised the Democratic National Committee starting in the summer of 2015.[3][4][5][6]

In April 2021, the US and UK governments attributed the SolarWinds Compromise to the SVR; public statements included citations to APT29, Cozy Bear, and The Dukes.[7][8] Industry reporting also referred to the actors involved in this campaign as UNC2452, NOBELIUM, StellarParticle, Dark Halo, and SolarStorm.[9][10][11][12][13][14]

Relationship explorer

All related ATT&CK context

Change history

Object version and sync metadata

The fields below describe the current mirrored snapshot. When Glexia retains multiple ATT&CK source imports, you can open the table to compare the same object across releases (hashes and MITRE timestamps). For MITRE’s own release notes and roadmap, see ATT&CK resources — Updates.

ATT&CK release: 19.2
Object version: 1.1
Created: Nov 16, 2021, 14:33 UTC (UTC+00:00)
Modified: Apr 11, 2024, 02:32 UTC (UTC+00:00)
Raw hash: 229ccb18cb17b9f0...

Imported snapshots across ATT&CK releases(2)

Release	Bundle imported	Object version	Modified	Status	Raw hash
19.2	Aug 6, 2026, 02:58 UTC (UTC+00:00)	1.1	Apr 11, 2024, 02:32 UTC (UTC+00:00)	Current bundle	`229ccb18cb17…`
19.1	Jul 14, 2026, 09:14 UTC (UTC+00:00)	1.1	Apr 11, 2024, 02:32 UTC (UTC+00:00)	Older bundle	`229ccb18cb17…`

Raw source

Mirrored ATT&CK source object

The raw object is retained through the mirrored ATT&CK source bundle and object hash. The raw endpoint returns the exact object from the mirrored bundle when available.

Open mirrored raw JSON Open MITRE-hosted copy

Source references

External references and citations

MITRE external references are preserved separately from Glexia analysis so citations remain traceable to their original source records.

[1]
MSTIC FoggyWeb September 2021
Ramin Nafisi. (2021, September 27). FoggyWeb: Targeted NOBELIUM malware leads to persistent backdoor. Retrieved October 4, 2021.
Open source URL
[2]
mitre-attackS0661
Open source URL

Source and licensing

Source: MITRE ATT&CK®. © 2026 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. MITRE ATT&CK and ATT&CK are registered trademarks of The MITRE Corporation. Glexia is not affiliated with or endorsed by MITRE.

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