Kelvir

Overview

Executive Summary

Propagation and Execution Lifecycle

• Instant Messaging Propagation (Worm Capability): Upon execution, Kelvir hooks into the active MSN Messenger process. It automatically sends a malicious link to every contact in the infected user's active contact list. The message often uses enticing social engineering (e.g., "lol check out this picture of you!") to trick the recipient into clicking the link.
• Payload Delivery: The link directs the recipient to a compromised web server that automatically downloads the Kelvir executable (often disguised as a `.scr`, `.pif`, or `.zip` file). If the new victim executes the file, the cycle repeats.
• System Sabotage and Backdoors: Once active, Kelvir attempts to disable local antivirus and firewall software. Crucially, many Kelvir variants carry a secondary payload—often a botnet agent or a backdoor trojan (like Spybot)—allowing the attacker to remotely control the infected machine, steal credentials, or launch DDoS attacks.

Threat Assessment

Eradication and Incident Response

• Aggressive Network Isolation: Infected machines must be immediately disconnected from the LAN to halt the outbound IM spam traffic and prevent further lateral spread.
• Application Control and Web Filtering: In modern environments, implement strict web filtering (SWG) to block the download of executable file types from unknown domains, neutralizing the worm's primary delivery mechanism.
• Behavioral EDR: Defenses must rely on heuristic EDR tools that detect anomalous actions (e.g., an IM client process unexpectedly attempting to download and execute secondary binaries, or modifications to the Windows `HOSTS` file).

Known aliases

Threat reports may refer to this family under multiple names:

• Worm.Win32.Kelvir
• IM-Worm.Kelvir
• W32/Kelvir

MITRE ATT&CK Techniques

This family has been observed using the following ATT&CK techniques: T1566.002 T1562.001 T1059

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.
• T1566.002: Inspect email links for known malicious domains and use link-rewriting services for time-of-click analysis.

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_KELVIR {
    meta:
        description = "Detects Kelvir (trojan)"
        author = "SystemHelpdesk Boilerplate Generator"
        date = "2026-07-06"
    strings:
        $s1 = "kelvir" ascii wide nocase
        $s2 = "worm.win32.kelvir" ascii wide nocase
        $s3 = "im-worm.kelvir" ascii wide nocase
        $s4 = "w32/kelvir" ascii wide nocase
    condition:
        uint16(0) == 0x5a4d and any of them
}

Sigma Rule

title: Suspicious Kelvir Activity
id: e09c40ea41b7c31c8d53d479eae32d34
status: experimental
description: Detects generic indicators of the kelvir malware family.
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell.exe'
        CommandLine|contains:
            - "*kelvir*"
            - "*worm.win32.kelvir*"
            - "*im-worm.kelvir*"
            - "*w32/kelvir*"
    condition: selection
level: medium

References & External Analysis

• Search "kelvir" on VirusTotal (External Analysis)

Frequently Asked Questions

Related Families (Category: trojan)

Explore other malware families in the same category:

• Gamethief
• Snarasite
• Cybergate
• Karagany
• Delfinject

Machine-readable

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