Oxypumper
Table of Contents
Overview
Oxypumper (tracked across endpoint security vendors and threat intelligence databases as VirTool:Win32/Oxypumper, Tool:Win32/Oxypumper, and HackTool:Win32/Oxypumper) is a specialized binary inflation and file-pumping utility active in cybercrime forums since 2015. Authored as a pre-distribution evasion tool, Oxypumper enables malware operators to artificially inflate the physical file size of compiled executables, dynamic link libraries, and payload stubs by padding them with megabytes of null bytes (0x00), repeated junk characters, or dummy resources. By ballooning small 200KB malware binaries into files exceeding 50MB, 100MB, or even 200MB, Oxypumper exploits hardcoded file size inspection limits in email security gateways, web proxies, and cloud sandbox platforms (which routinely bypass deep analysis on oversized files to preserve processing throughput).
Known aliases
Threat reports may refer to this family under multiple names:
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: Virtool:Win32/Oxypumper.A · Tool:Win32/Oxypumper.Gen
MITRE ATT&CK Techniques
This family has been observed using the following ATT&CK techniques: T1027.001 · T1497.001 · T1036 · T1204.002 · T1140
Tactical Mitigations
Based on the techniques used by this family, consider the following defensive strategies:
- T1036: Monitor for executable files running from unusual paths or with deceptive names. Use EDR to detect process masquerading.
MITRE D3FEND™ Defensive Countermeasures
Defensive techniques mapped to counter the offensive tradecraft observed in this family (via the MITRE D3FEND matrix):
| D3FEND ID | Countermeasure Name | Tactic | Countered ATT&CK | Defensive Guidance |
|---|---|---|---|---|
D3-BDA | Binary De-obfuscation & Unpacking | Analyze | T1027.001 | Utilize memory dump scanners and entropy inspection to unpack encrypted stagers during process creation. |
D3-PMA | Process Lineage & Masquerade Analysis | Detect | T1036 | Verify digital code-signing signatures and compare executable paths against known Windows binaries. |
D3-FEA | File Execution Analysis | Harden | T1204.002 | Enforce AppLocker and Windows Defender Application Control (WDAC) to block executable launches from temporary and user-writable directories. |
D3-EED | Execution Environment Detection | Detect | T1497.001 | Configure malware sandboxes to emulate legitimate hardware metrics, realistic mouse movements, and valid system uptimes. |
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:
Tier 1 Primitive Artifact Rule (Fast Triage)
Matches raw strings and file markers. Vulnerable to binary repacking and simple obfuscation.
rule MALWARE_WIN_OXYPUMPER_T1_ARTIFACT {
meta:
description = "Tier 1 Primitive Artifact: Raw string matches for Oxypumper"
tier = "T1 - Primitive Artifact"
confidence = "Low-Medium (Fast Triage)"
author = "SystemHelpdesk Threat Research Desk"
date = "2026-10-14"
strings:
$s1 = "oxypumper" ascii wide nocase
$s2 = "virtool:win32/oxypumper" ascii wide nocase
$s3 = "tool:win32/oxypumper" ascii wide nocase
$s4 = "hacktool:win32/oxypumper" ascii wide nocase
$s5 = "win32/oxypumper" ascii wide nocase
$s6 = "oxyfilepumper" ascii wide nocase
condition:
uint16(0) == 0x5a4d and any of them
}Tier 2 Behavioral Context Rule (Process Chains & Sigma)
Tracks parent-child process anomalies and suspicious scripting telemetry. Resilient against file renames.
title: SystemHelpDesk Detection - Oxypumper (Pua Tool) Execution & Triage
id: 07ceedd2-1126-5820-b884-aa956dca273e
status: production
description: Detects execution, defense evasion, and persistence behaviors associated
with the Oxypumper 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/oxypumper
- 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.pua-tool
- author.ricky-jordan
- source.systemhelpdesk-mfc
- attack.t1027_001
- attack.t1497_001
- attack.t1036
- attack.t1204_002
- attack.t1140
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: mediumTier 3 Attribution Fingerprint Rule (High Fidelity)
Deep signature matching distinctive operational fingerprints and payload characteristics.
rule MALWARE_WIN_OXYPUMPER_T3_ATTRIBUTION {
meta:
description = "Tier 3 Attribution Fingerprint: Heuristic detection for Oxypumper 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 = "oxypumper" 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 Defender Threat Encyclopedia - VirTool:Win32/Oxypumper
- Trend Micro Threat Encyclopedia - Tool.Win32.Oxypumper
- Search "oxypumper" on VirusTotal (External Analysis)
- Search "oxypumper" on Any.Run (Sandbox Sandbox)
- Search "oxypumper" on MalwareBazaar (Malware Samples)
Frequently Asked Questions
What is VirTool:Win32/Oxypumper?
Oxypumper is a file-pumping utility used by malware authors to artificially inflate the size of executable files with null bytes or dummy data.
Why do malware authors artificially pump file sizes?
Many email security gateways and automated cloud sandboxes skip deep analysis on files exceeding 50MB or 100MB to conserve scanning bandwidth.
How does Oxypumper add bulk to a binary without corrupting it?
It appends junk data to the overlay area at the end of the PE file or inflates the .rsrc resource section while keeping valid header offsets intact.
Can security software detect files inflated by Oxypumper?
Yes, modern scanners inspect PE overlay ratios, strip trailing null bytes, and calculate entropy anomalies to identify pumped binaries.
What types of malware commonly utilize file pumping?
Threat actors use file pumpers on initial access loaders, ransomware droppers, and infostealers distributed via email attachments or download links.
How do I remove the Oxypumper Pua_Tool from Windows?
Manual removal of Oxypumper is highly discouraged as it may leave persistence mechanisms intact. We recommend disconnecting the device from the internet and utilizing a professional incident response service or enterprise-grade EDR software to conduct a full forensic sweep.
Is Oxypumper a virus or a Pua_Tool?
Oxypumper is classified as a Pua_Tool. Unlike traditional viruses that infect files, modern malware like Oxypumper typically operates as a standalone payload designed to compromise systems, steal data, or deploy secondary stage implants.
What are the main symptoms of a Oxypumper infection?
Symptoms of Oxypumper can include unexpected system slowness, unauthorized outbound network traffic to unknown IP addresses, disabled security software, and suspicious background processes running from AppData or Temp directories.
Protect Your Network Against Pua_Tools
Want to prevent Oxypumper and similar threats from compromising your organization? Read our comprehensive defensive guide: Think You've Been Hacked? What To Do First.
📣 Threat Intel Correction or Update?
Notice an outdated IOC, unlisted alias, or disputed attribution? Threat researchers are invited to propose an update on GitHub or contact the SystemHelpDesk research desk. All community revisions are credited in our public CHANGELOG.
Machine-readable
Get this profile as JSON: https://malware-families-catalog.systemhelpdesk.com/api/oxypumper.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.