Malware often uses custom user agent strings to evade detection and communicate with command-and-control servers. SOC teams should proactively hunt for these suspicious user agents in Azure Sentinel to identify potential malware activity and prevent data exfiltration or system compromise.
Detection Rule
title: Malware User Agent
id: 5c84856b-55a5-45f1-826f-13f37250cf4e
status: test
description: Detects suspicious user agent strings used by malware in proxy logs
references:
- http://rules.emergingthreats.net/open/snort-2.9.0/rules/emerging-user_agents.rules
- http://www.botopedia.org/search?searchword=scan&searchphrase=all
- https://networkraptor.blogspot.com/2015/01/user-agent-strings.html
- https://perishablepress.com/blacklist/ua-2013.txt
- https://www.bluecoat.com/en-gb/security-blog/2015-05-05/know-your-agents
- https://twitter.com/kladblokje_88/status/1614673320124743681?s=12&t=joEpeVa5d58aHYNGA_To7Q
- https://pbs.twimg.com/media/FtYbfsDXoAQ1Y8M?format=jpg&name=large
- https://twitter.com/crep1x/status/1635034100213112833
author: Florian Roth (Nextron Systems), X__Junior (Nextron Systems), Nasreddine Bencherchali (Nextron Systems)
date: 2017-07-08
modified: 2024-04-14
tags:
- attack.command-and-control
- attack.t1071.001
logsource:
category: proxy
detection:
selection:
c-useragent:
# RATs
- 'Mozilla/5.0 (Windows NT 6.1; WOW64; rv:53.0) Gecko/20100101 Chrome /53.0' # DragonOK
- 'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1)' # Used by PlugX - base-lining recommended - https://community.rsa.com/thread/185439
- 'Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0)' # Used by PlugX - base-lining recommended - https://community.rsa.com/thread/185439
- 'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 1.1.4322)' # Used by PlugX - old - https://unit42.paloaltonetworks.com/unit-42-identifies-new-dragonok-backdoor-malware-deployed-against-japanese-targets/
- 'HttpBrowser/1.0' # HTTPBrowser RAT
- '*<|>*' # Houdini / Iniduoh / njRAT
- 'nsis_inetc (mozilla)' # ZeroAccess
- 'Wget/1.9+cvs-stable (Red Hat modified)' # Dyre / Upatre
# Ghost419 https://www.mcafee.com/blogs/other-blogs/mcafee-labs/gold-dragon-widens-olympics-malware-attacks-gains-permanent-presence-on-victims-systems/
- 'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; .NET CLR 1.1.4322)'
# Malware
- '*zeroup*' # W32/Renos.Downloader
- 'Mozilla/5.0 (Windows NT 5.1 ; v.*' # Kazy
- '* adlib/*'
- '* tiny' # Trojan Downloader
- '* BGroom *' # Trojan Downloader
- '* changhuatong'
- '* CholTBAgent'
- 'Mozilla/5.0 WinInet'
- 'RookIE/1.0'
- 'M' # HkMain
- 'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)' # Egamipload - old UA - probable prone to false positives
- 'Mozilla/4.0 (compatible;MSIE 7.0;Windows NT 6.0)' # Yakes
- 'backdoorbot'
- 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.1 (.NET CLR 3.5.30731)' # Sality
- 'Opera/8.81 (Windows NT 6.0; U; en)' # Sality
- 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.1 (.NET CLR 3.5.30729)' # Sality
- 'Opera' # Trojan Keragany
- 'Mozilla/4.0 (compatible; MSIE 5.0; Windows 98)' # Fareit
- 'Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)' # Webshell's back connect
- 'MSIE' # Toby web shell
- '*(Charon; Inferno)' # Loki Bot
- 'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/5.0)' # Fareit / Pony
- 'Mozilla/4.0 (compatible; MSIE 6.1; Windows NT)' # https://www.virustotal.com/gui/file/8abbef8e58f012d45a7cb46c3c2729dcd33cf53e721ff8c59e238862aa0a9e0e/detection
- 'Mozilla/4.0(compatible; MSIE 6.0; Windows NT 5.1)' # MacControl malware https://www.virustotal.com/gui/file/d60f61f1f03a5011a0240694e110c6d370bf68a92753093186c6d14e26a15428/detection https://www.symantec.com/connect/blogs/osxmacontrol-back-it-again
- 'Mozilla/5.0 (Windows NT 10.0; Win64; x64)' # used by Zebrocy malware https://app.any.run/tasks/7d7fa4a0-6970-4428-828b-29572abf9ceb/
# Ursnif
- 'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 10.0; Win64; x64)'
- 'Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64)'
# Emotet
- 'Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.2; WOW64; Trident/7.0; .NET4.0C; .NET4.0E; InfoPath.3)' # https://twitter.com/webbthewombat/status/1225827092132179968
# Lockbit (https://twitter.com/kladblokje_88/status/1614673320124743681?s=12&t=joEpeVa5d58aHYNGA_To7Q)
- 'Mozilla/5.0 (Windows NT 6.1)'
- 'AppleWebkit/587.38 (KHTML, like Gecko)'
- 'Chrome/91.0.4472.77'
- 'Safari/537.36'
- 'Edge/91.0.864.37'
- 'Firefox/89.0'
- 'Gecko/20100101'
# Others
- '* pxyscand*'
- '* asd'
- '* mdms'
- 'sample'
- 'nocase'
- 'Moxilla'
- 'Win32 *'
- '*Microsoft Internet Explorer*'
- 'agent *'
- 'AutoIt' # Suspicious - base-lining recommended
- 'IczelionDownLoad'
- 'Mozilla/4.0 (compatible; MSIE 9.0; Windows NT 10.0; .NET4.0C; .NET4.0E; Tablet PC 2.0)' # https://unit42.paloaltonetworks.com/thor-plugx-variant/
- 'record' # https://blog.sekoia.io/raccoon-stealer-v2-part-1-the-return-of-the-dead/
- 'mozzzzzzzzzzz' # https://blog.sekoia.io/raccoon-stealer-v2-part-1-the-return-of-the-dead/
- 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:76.0) Gecko/20100101 Firefox/76.0' # Quasar RAT UA https://twitter.com/malmoeb/status/1559994820692672519?s=20&t=g3tkNL09dZZWbFN10qDVjg
- 'Havana/0.1' # https://www.cybereason.com/blog/threat-alert-havanacrypt-ransomware-masquerading-as-google-update
- 'antSword/v2.1' # AntSword Webshell UA
- 'rqwrwqrqwrqw' # Racoon Stealer
- 'qwrqrwrqwrqwr' # Racoon Stealer
- 'rc2.0/client' # Racoon Stealer
- 'TakeMyPainBack' # Racoon Stealer
- 'xxx' # Racoon Stealer
- '20112211' # Racoon Stealer
- '23591' # Racoon Stealer
- '901785252112' # Racoon Stealer
- '1235125521512' # Racoon Stealer
- '125122112551' # Racoon Stealer
- 'B1D3N_RIM_MY_ASS' # Racoon Stealer
- 'AYAYAYAY1337' # Racoon Stealer
- 'iMightJustPayMySelfForAFeature' # Racoon Stealer
- 'ForAFeature' # Racoon Stealer
- 'Ares_ldr_v_*' # AresLoader
# - 'Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:106.0) Gecko/20100101 Firefox/106' # seen used by AresLoader
- 'Microsoft Internet Explorer' # https://github.com/silence-is-best/c2db
- 'CLCTR' # https://github.com/silence-is-best/c2db
- 'uploader' # https://github.com/silence-is-best/c2db
- 'agent' # https://github.com/silence-is-best/c2db
- 'License' # https://github.com/silence-is-best/c2db
- 'vb wininet' # https://github.com/silence-is-best/c2db
- 'Client' # https://github.com/silence-is-best/c2db
- 'Lilith-Bot/3.0' # Lilith Stealer - https://twitter.com/suyog41/status/1558051450797690880
- 'svc/1.0' # SVC Loader - https://twitter.com/suyog41/status/1558051450797690880
- 'WSHRAT' # WSHRAT - https://twitter.com/suyog41/status/1558051450797690880
- 'ZeroStresser Botnet/1.5' # Zerobot - https://twitter.com/suyog41/status/1558051450797690880
- 'OK' # Nymaim - https://twitter.com/suyog41/status/1558051450797690880
- 'Project1sqlite' # DarkCloud - https://twitter.com/suyog41/status/1558051450797690880
- 'Project1' # DarkCloud - https://twitter.com/suyog41/status/1558051450797690880
- 'DuckTales' # Racoon Stealer
- 'Zadanie' # Racoon Stealer
- 'GunnaWunnaBlueTips' # Racoon Stealer
- 'Xlmst' # Racoon Stealer
- 'GeekingToTheMoon' # Racoon Stealer
- 'SunShineMoonLight' # Racoon Stealer
- 'BunnyRequester' # BunnyStealer
- 'BunnyTasks' # BunnyStealer
- 'BunnyStealer' # BunnyStealer
- 'BunnyLoader_Dropper' # BunnyStealer
- 'BunnyLoader' # BunnyStealer
- 'BunnyShell' # BunnyStealer
- 'SPARK-COMMIT' # SparkRAT - https://arcticwolf.com/resources/blog/tellmethetruth-exploitation-of-cve-2023-46604-leading-to-ransomware/
- '4B4DB4B3' # B4B3RAT - https://twitter.com/naumovax/status/1718956514491130301
- 'SouthSide' # Racoon Stealer
- 'Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Tob 1.1)' # Latrodectus loader
condition: selection
falsepositives:
- Unknown
level: high
imWebSession
| where HttpUserAgent in~ ("Mozilla/5.0 (Windows NT 6.1; WOW64; rv:53.0) Gecko/20100101 Chrome /53.0", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1)", "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Trident/4.0)", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; .NET CLR 1.1.4322)", "HttpBrowser/1.0", "nsis_inetc (mozilla)", "Wget/1.9+cvs-stable (Red Hat modified)", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Trident/4.0; .NET CLR 1.1.4322)", "Mozilla/5.0 WinInet", "RookIE/1.0", "M", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0)", "Mozilla/4.0 (compatible;MSIE 7.0;Windows NT 6.0)", "backdoorbot", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.1 (.NET CLR 3.5.30731)", "Opera/8.81 (Windows NT 6.0; U; en)", "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.3) Gecko/20100401 Firefox/3.6.1 (.NET CLR 3.5.30729)", "Opera", "Mozilla/4.0 (compatible; MSIE 5.0; Windows 98)", "Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)", "MSIE", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/5.0)", "Mozilla/4.0 (compatible; MSIE 6.1; Windows NT)", "Mozilla/4.0(compatible; MSIE 6.0; Windows NT 5.1)", "Mozilla/5.0 (Windows NT 10.0; Win64; x64)", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 10.0; Win64; x64)", "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; Win64; x64)", "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.2; WOW64; Trident/7.0; .NET4.0C; .NET4.0E; InfoPath.3)", "Mozilla/5.0 (Windows NT 6.1)", "AppleWebkit/587.38 (KHTML, like Gecko)", "Chrome/91.0.4472.77", "Safari/537.36", "Edge/91.0.864.37", "Firefox/89.0", "Gecko/20100101", "sample", "nocase", "Moxilla", "AutoIt", "IczelionDownLoad", "Mozilla/4.0 (compatible; MSIE 9.0; Windows NT 10.0; .NET4.0C; .NET4.0E; Tablet PC 2.0)", "record", "mozzzzzzzzzzz", "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:76.0) Gecko/20100101 Firefox/76.0", "Havana/0.1", "antSword/v2.1", "rqwrwqrqwrqw", "qwrqrwrqwrqwr", "rc2.0/client", "TakeMyPainBack", "xxx", "20112211", "23591", "901785252112", "1235125521512", "125122112551", "B1D3N_RIM_MY_ASS", "AYAYAYAY1337", "iMightJustPayMySelfForAFeature", "ForAFeature", "Microsoft Internet Explorer", "CLCTR", "uploader", "agent", "License", "vb wininet", "Client", "Lilith-Bot/3.0", "svc/1.0", "WSHRAT", "ZeroStresser Botnet/1.5", "OK", "Project1sqlite", "Project1", "DuckTales", "Zadanie", "GunnaWunnaBlueTips", "Xlmst", "GeekingToTheMoon", "SunShineMoonLight", "BunnyRequester", "BunnyTasks", "BunnyStealer", "BunnyLoader_Dropper", "BunnyLoader", "BunnyShell", "SPARK-COMMIT", "4B4DB4B3", "SouthSide", "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; Tob 1.1)") or HttpUserAgent contains "<|>" or HttpUserAgent contains "zeroup" or HttpUserAgent startswith "Mozilla/5.0 (Windows NT 5.1 ; v." or HttpUserAgent contains " adlib/" or HttpUserAgent endswith " tiny" or HttpUserAgent contains " BGroom " or HttpUserAgent endswith " changhuatong" or HttpUserAgent endswith " CholTBAgent" or HttpUserAgent endswith "(Charon; Inferno)" or HttpUserAgent contains " pxyscand" or HttpUserAgent endswith " asd" or HttpUserAgent endswith " mdms" or HttpUserAgent startswith "Win32 " or HttpUserAgent contains "Microsoft Internet Explorer" or HttpUserAgent startswith "agent " or HttpUserAgent startswith "Ares_ldr_v_"Scenario: System Maintenance Task Using a Known Malware User Agent
Description: A legitimate system maintenance task (e.g., Windows Task Scheduler running schtasks.exe) may use a user agent string that matches a known malware pattern.
Filter/Exclusion: Exclude processes initiated by the Task Scheduler or processes with CommandLine containing schtasks.exe or at.exe.
Scenario: Admin Access via Proxy with Custom User Agent
Description: An administrator might use a custom user agent string (e.g., Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36) for testing or monitoring purposes.
Filter/Exclusion: Exclude traffic originating from admin IP ranges or user agents that match known admin tools (e.g., curl, wget, Postman).
Scenario: Scheduled Job Using a Legitimate Tool with Mismatched User Agent
Description: A scheduled job using a tool like curl or PowerShell might send a request with a user agent string that appears suspicious due to formatting or misconfiguration.
Filter/Exclusion: Exclude requests with User-Agent matching curl/7.81.0 or PowerShell/7.2.5 or those originating from a known job scheduler (e.g., crontab, jenkins, Azure DevOps).
Scenario: Proxy Log Anomalies from Internal Monitoring Tools
Description: Internal monitoring tools (e.g., Prometheus, Grafana, ELK Stack) may generate proxy logs with user agents that resemble malware patterns.
Filter/Exclusion: Exclude traffic