Formbook

Overview

Formbook (rebranded in recent generations as XLoader) is a prolific, cross-platform information stealer and spyware implant offered on underground cybercrime forums as a rental service since early 2016. Originally authored by a developer known as 'ng2000', Formbook was engineered to harvest credentials and surveillance telemetry while evading advanced endpoint detection systems. Formbook hooks window messaging routines and browser networking APIs to capture keystrokes, clipboard contents, and submitted web forms (including banking credentials and logins) before TLS encryption. It features a sophisticated decoy command and control mechanism: in every communication cycle, Formbook dispatches HTTP requests to dozens of legitimate decoy domains (such as university or news websites) intermingled with a single encrypted payload sent to the real C2 gate. In 2020, the developers expanded the codebase to target Apple macOS under the name XLoader, establishing it as one of the few truly cross-platform commercial spyware offerings extensively leveraged in Business Email Compromise (BEC) and corporate espionage.

Known aliases

Threat reports may refer to this family under multiple names:

• Formbook
• XLoader
• InfoStealer.FormBook
• Trojan.FormGrabber
• Win32/FormBook

Threat Actor Attribution

Attribution is probabilistic, not a science. Each link below states its confidence level and the evidence behind it.

• ng2000 / Commercial MaaS Syndicate (Rebranded as XLoader) High confidence
  Basis: Originally created in 2016 by author 'ng2000' and rented on underground forums as Formbook. Rebranded in 2020 as XLoader with cross-platform support for Microsoft Windows and Apple macOS. Heavily leveraged by Business Email Compromise (BEC) syndicates and commodity cybercrime groups worldwide. [source]

Family Pedigree & Lineage

Malware authors regularly fork and iterate upon existing codebases. Observed upstream lineage and downstream variants for this family include:

Known Derivatives & Downstream Variants: Formbook V4 · Xloader-Win · Xloader-Mac

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to our technical analysis hubs and the official MITRE ATT&CK framework:

Tactical Mitigations

Based on the techniques used by this family, consider the following defensive strategies:

• T1056.001: Implement Endpoint Detection and Response (EDR) to monitor for suspicious API calls related to keystroke interception. Enforce Multi-Factor Authentication (MFA) to render stolen passwords useless.
• T1566.001: Scan email attachments for malicious macros, scripts, or suspicious archive files.

MITRE D3FEND™ Defensive Countermeasures

Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):

Exploited Vulnerabilities (CVEs)

This malware family is documented weaponizing the following common vulnerabilities and exposures:

• CVE-2017-11882 — In-depth exploitation analysis and catalog intelligence (NIST NVD ↗).
• CVE-2021-40444 — In-depth exploitation analysis and catalog intelligence (NIST NVD ↗).

Command & Control (C2) and Network Profile

How this family talks to its operators. C2 traffic can often identify a family even when its code and configuration are hard to analyse. Ports and patterns are historical and change between campaigns, so use them as hunting leads rather than block-only rules.

Network detection ideas

• Detect anomalous patterns of rapid sequential HTTP requests to dozens of unrelated websites originating from non-browser system processes (e.g. explorer.exe or svchost.exe)
• Block known Formbook/XLoader C2 gate URLs and decoys cataloged by threat intelligence feeds
• Monitor for process hollowing injection where newly spawned Windows utility binaries immediately initiate outbound network connections

Sources: CISA Advisory AA20-302A, MITRE ATT&CK S0663: XLoader

Indicators of Compromise

Public indicators drawn from CISA advisories and vendor reporting. These are historical and intended for retrospective threat hunting; current campaigns may use different infrastructure. SystemHelpDesk adheres to responsible disclosure and does not host live samples.

File hashes (SHA-256, sample)

Cryptographic hashes serve as reference indicators for triage and detection rules. In accordance with responsible threat intelligence disclosure, this catalog indexes reference metadata and does not host or distribute live malware binaries.

• 0a0b9875e6382a17cfc1f44d82ef2b0cbe7a13d31707963d4e0ce1d0449265f2
• d92b34a1a5b81a5f6a98df85cfbc9d1469e3240e9ec41b94d7d3d758c0678f8d

Delivery vectors

• Spear-phishing emails containing weaponized ISO, RAR, or ZIP archives
• Office documents exploiting CVE-2017-11882 or CVE-2021-40444

Persistence mechanisms

• Process hollowing injecting into explorer.exe or signed Windows binaries
• Run registry keys with randomized names; execution from %APPDATA% directory

Detection Guidance

Detection ideas drawn from public reporting. Tune to your environment before deploying.

• Suricata FormBook C2 ruleset
• EDR rule for process hollowing of explorer.exe at startup
• YARA rule FormBook_Stealer

Tiered Detection Rules (Cisco CAIRN Model)

Modern threat detection requires multi-layered rule engineering. We classify detections into three operational tiers based on signal fidelity:

rule MALWARE_WIN_FORMBOOK_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Formbook"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "formbook" ascii wide nocase
        $s2 = "formbook" ascii wide nocase
        $s3 = "xloader" ascii wide nocase
        $s4 = "infostealer.formbook" ascii wide nocase
        $s5 = "trojan.formgrabber" ascii wide nocase
        $s6 = "win32/formbook" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Formbook (Spyware) Execution & Triage
id: 2019b411-8ac1-5145-b737-2af9f96631b7
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Formbook malware family. Detects suspicious execution from temporary user
  directories with hidden window flags and background transfer utilities.
references:
- https://malware-families-catalog.systemhelpdesk.com/families/formbook
- https://malware-families-catalog.systemhelpdesk.com/defensive/ransomware-protection
- https://malware-families-catalog.systemhelpdesk.com/
author: Ricky Jordan, Lead Threat Intelligence Analyst, SystemHelpDesk MSP
date: '2026-10-14'
modified: '2026-10-14'
tags:
- attack.spyware
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1056_001
- attack.t1555_003
- attack.t1055
- attack.t1041
- attack.t1566_001
logsource:
  category: process_creation
  product: windows
detection:
  selection_process:
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \cscript.exe
    - \wscript.exe
    CommandLine|contains:
    - AppData\Local\Temp
    - -WindowStyle Hidden
    - /e:jscript
    - bitsadmin /transfer
  condition: selection_process
falsepositives:
- Legitimate enterprise administrative scripts during approved change windows
- Authorized IT software deployment utilities and backup management agents
level: medium

rule MALWARE_WIN_FORMBOOK_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Formbook tradecraft"
        tier = "T3 - Attribution Fingerprint"
        confidence = "High (Confirmed Family Signature)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        // Core family identifier & heuristic payload signatures
        $attrib_str = "formbook" ascii wide nocase
        $pe_magic = "MZ" ascii
        $net_marker = "http" ascii nocase
    condition:
        uint16(0) == 0x5a4d and ($attrib_str and $net_marker) and filesize < 15MB
}

Containment & Response Steps

Ordered checklist for responders. Adapt to your environment and engage professional support for active incidents.

1. Isolate host and collect volatile memory
2. Rotate all browser-stored and FTP-client credentials
3. Block C2 gate URLs at perimeter and DNS
4. Audit other hosts in the org receiving the same phishing lure

What to Avoid

Common mistakes during response to this family that can destroy evidence, spread the infection, or worsen recovery.

1. Do not rely on disk-based AV scans alone — FormBook often runs in memory only
2. Do not assume container files like ISO are safe to open
3. Do not delay credential rotation

References & External Analysis

• MITRE ATT&CK: XLoader / FormBook (S1207)
• CISA Advisory: CISA Alert AA20-302A (Top Routinely Exploited Vulnerabilities)
• Search "formbook" on VirusTotal (External Analysis)
• Search "formbook" on Any.Run (Sandbox Sandbox)
• Search "formbook" on MalwareBazaar (Malware Samples)

North American Authority Advisory (CISA / NIST)

The Cybersecurity and Infrastructure Security Agency (CISA) has published an official US federal advisory on this family, which can be mapped to NIST Cybersecurity Framework (CSF) incident response controls: CISA Alert AA20-302A (Top Routinely Exploited Vulnerabilities) ↗

Frequently Asked Questions

Related Threats (Category: Spyware)

Explore other documented threats in the same operational category:

• Pegasus
• Predator
• Fearless_Key_Spy
• Relevantknowledge
• Candiru
• Webwatcher
• Freekeylogger
• Fearless_Lite

Machine-readable

Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/formbook.json

Ecosystem & Interactive Environments

This profile is part of the Malware Families Catalog, a public dataset of 2,899 malware families. The catalog is also published across our ecosystem: Hugging Face, Kaggle, Zenodo, Replit, StackBlitz, CodeSandbox, and CodePen.