Sasser

Overview

Sasser (classified across antivirus vendors as W32.Sasser, Worm.Win32.Sasser, and Win32/Sasser) is one of the most disruptive self-replicating computer worms in the history of the internet, authored by 17-year-old German high school student Sven Jaschan (who also created the Netsky mass-mailing worm) and unleashed on April 30, 2004. Unlike conventional email worms of the era that required users to open an infected attachment, Sasser was completely autonomous: it scanned random IP addresses on TCP port 445 looking for unpatched systems running Microsoft Windows 2000, Windows XP, and Windows Server 2003. When an open system was identified, Sasser exploited a critical stack buffer overflow in the Local Security Authority Subsystem Service (LSASS) via the DsRolerUpgradeDownlevelServer RPC API (CVE-2004-0280 / MS04-011). The exploit triggered arbitrary shellcode execution, opening a remote command shell on TCP port 9996 and downloading the full worm executable ('avserve.exe' or 'avserve2.exe') from the attacking host via an FTP server spawned on TCP port 5554. Sasser caused lsass.exe to terminate with an unhandled exception (status code 0xC0000005), which forced Windows to display a critical system dialog with a 60-second countdown timer before automatically restarting the computer. The worm spread with such exponential ferocity that within 48 hours it infected millions of computers globally, grounding Delta Air Lines flights, closing one-third of post offices in Taiwan, halting satellite communications for French news agency AFP, and paralyzing operations at British investment banks and public hospitals. Jaschan was arrested in May 2004 following a joint investigation by German police and Microsoft.

Known aliases

Threat reports may refer to this family under multiple names:

• W32.Sasser
• Worm.Win32.Sasser
• Win32/Sasser.A
• Sasser Worm
• W32/Sasser.worm

Family Pedigree & Lineage

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

Derived From / Upstream Ancestry: Netsky

Known Derivatives & Downstream Variants: Sasser_A · Sasser_B · Sasser_C · Sasser_D

MITRE ATT&CK Techniques

This family has been observed using the following ATT&CK techniques: T1210 · T1059 · T1547.001 · T1083 · T1498

Tactical Mitigations

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

• T1059: Restrict execution of scripting languages such as PowerShell, VBScript, or Python to authorized administrators. Enforce Script Block Logging.

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-2004-0280 — In-depth exploitation analysis and catalog intelligence (NIST NVD ↗).

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.

• a172776c59b67195721118182969b761a17387f5df2307ef086915091219b671
• 5b508f72a4209bf26efba098b671a52028ddc87c14a22ad31737be70d8a57102

Delivery vectors

• Autonomous network worm propagation exploiting LSASS buffer overflow CVE-2004-0280 over SMB TCP port 445
• Automated FTP payload transfer on TCP port 5554 spawning remote shell on port 9996

Persistence mechanisms

• Registry Run key under HKLM\Software\Microsoft\Windows\CurrentVersion\Run pointing to avserve.exe in %WINDIR%
• Automatic spawning of background scanning threads upon user login

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_SASSER_T1_ARTIFACT {
    meta:
        description = "Tier 1 Primitive Artifact: Raw string matches for Sasser"
        tier = "T1 - Primitive Artifact"
        confidence = "Low-Medium (Fast Triage)"
        author = "SystemHelpdesk Threat Research Desk"
        date = "2026-10-14"
    strings:
        $s1 = "sasser" ascii wide nocase
        $s2 = "w32.sasser" ascii wide nocase
        $s3 = "worm.win32.sasser" ascii wide nocase
        $s4 = "win32/sasser.a" ascii wide nocase
        $s5 = "sasser worm" ascii wide nocase
        $s6 = "w32/sasser.worm" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

title: SystemHelpDesk Detection - Sasser (Worm) Execution & Triage
id: dac26e01-a85f-550d-8e51-9e67f9b20fbe
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
  with the Sasser 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/sasser
- 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.worm
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1210
- attack.t1059
- attack.t1547_001
- attack.t1083
- attack.t1498
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_SASSER_T3_ATTRIBUTION {
    meta:
        description = "Tier 3 Attribution Fingerprint: Heuristic detection for Sasser 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 = "sasser" 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
}

References & External Analysis

• Microsoft Security Bulletin MS04-011: Security Update for Microsoft Windows (835732)
• F-Secure Threat Description: Sasser Worm
• BBC News: Sasser Worm Disrupts Global Systems
• Search "sasser" on VirusTotal (External Analysis)
• Search "sasser" on Any.Run (Sandbox Sandbox)
• Search "sasser" on MalwareBazaar (Malware Samples)

Frequently Asked Questions

Related Threats (Category: Worm)

Explore other documented threats in the same operational category:

• Chir
• Ngrbot
• Brontok
• Allaple
• Ludbaruma
• Cambot
• Brambul
• Conficker

Machine-readable

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