Bobax

Overview

Worm:Win32/Bobax is a classic, historically significant computer worm and botnet agent known for its aggressive propagation mechanisms and its primary function of transforming infected machines into massive spam relays (zombies). Emerging in the mid-2000s, Bobax was a major player in the global botnet ecosystem, frequently utilized by cybercriminal syndicates to blast out pharmaceutical spam, phishing emails, and distribute other malware.

Understanding the Bobax Worm
To an end-user, a Bobax infection might cause severe internet slowdowns and system sluggishness due to the massive volume of outbound email traffic. For a network administrator, Bobax is a severe threat that can quickly result in the organization's IP space being blacklisted by global anti-spam organizations (like Spamhaus), crippling legitimate corporate email communications.

Execution and Spreading Mechanics
Bobax primarily propagated by actively scanning the internet for machines vulnerable to known Windows exploits, most notably the LSASS vulnerability (MS04-011) and the RPC/DCOM vulnerability (MS03-026) (`T1210`). Once a vulnerable machine was found, Bobax exploited it to execute a remote shell and download a copy of itself. Upon execution, it dropped a copy into the `System32` directory and established persistence via the Registry Run keys or by injecting itself into the `svchost.exe` process (`T1543.003`, `T1055`). It then reached out to a hardcoded list of C2 servers (or used peer-to-peer mechanisms in later variants) to download spam templates and lists of target email addresses. Finally, it established its own internal SMTP engine to blast out thousands of spam emails directly from the victim's machine (`T1498.002`).

Indicators of Compromise & Impact
The impact was severe network congestion, IP blacklisting, and participation in global cybercrime. Host-based IoCs included `svchost.exe` utilizing high CPU and memory, and establishing thousands of outbound connections on port 25 (SMTP). Network IoCs were dominated by massive, anomalous spikes in outbound SMTP traffic originating from standard workstations (which should normally only talk to the corporate Exchange server).

MITRE ATT&CK Techniques

Observed techniques used by this family, mapped to the MITRE ATT&CK framework:

Generated Detections (Boilerplate)

These YARA and Sigma rules are auto-generated based on the family name and aliases. They must be heavily tuned before deployment in a production environment.

YARA Rule

rule MALWARE_WIN_BOBAX {
    meta:
        description = "Detects Bobax (advanced_threat)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "bobax" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Bobax Activity
id: 339ba7c37d9d31e681a6e764172ecafc
status: experimental
description: Detects generic indicators of the bobax malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*bobax*"
    condition: selection
level: medium

Containment & Response Steps

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

1. Immediately isolate the infected endpoint from the network to stop the outbound spam flood and prevent the IP from being blacklisted.
2. Block outbound port 25 (SMTP) traffic from all endpoints at the perimeter firewall, allowing only the designated corporate email servers to send mail.
3. Ensure all legacy Windows systems are patched against MS04-011 and MS03-026, or decommissioned entirely.
4. Monitor IP reputation services (like MXToolbox) to ensure the organization's public IP has not been blacklisted due to the Bobax activity.

What to Avoid

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

1. Do not allow standard workstations direct outbound access to the internet on port 25; this is the primary enabler for spam botnets.
2. Avoid relying solely on local AV scans, as worms like Bobax heavily utilize process injection to hide from standard file-based detection.

References & External Analysis

• Search "bobax" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: advanced_threat)

Explore other malware families in the same category:

• Refog
• Vrbrothers
• Dlassistant
• Installpack
• Bang5Mai

Machine-readable

Get this profile as JSON: https://jordan123234-malware-families-explorer.static.hf.space/api/bobax.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.