MalwareUsed by 3 actors

RainyDay

RainyDay, also known as FoundCore, is a Windows backdoor associated with the China-linked Naikon espionage group. It has been used as a first-stage implant in intrusions targeting military and government-related organizations in Southeast Asia, where it served as an access platform for reconnaissance, persistence, tool deployment, and delivery of additional payloads including the Nebulae backdoor.

RainyDay supports remote command-and-control over both TCP and HTTP and can switch between those protocols when one channel is unavailable, improving communication resilience. Its communications have been observed protected with RC4, and payload components may be decrypted with XOR-based routines. The malware can enumerate processes, access a command shell, capture screenshots, manipulate files, and support collection and exfiltration of data. Reported follow-on tooling used alongside RainyDay included utilities for harvesting credentials from web browsers and collecting recently changed files for exfiltration, including staging data locally and uploading selected files to cloud storage.

For persistence and execution, RainyDay has used Windows scheduled tasks and services, and it has also been launched through DLL side-loading techniques. It has employed masquerading by adopting names resembling legitimate software components. The malware also includes self-removal functionality, allowing operators to uninstall it by deleting its service and associated files.

Operationally, RainyDay has been linked to broader Naikon tradecraft that included reconnaissance, password dumping, lateral movement, and deployment of secondary tools in long-running cyber-espionage campaigns. Its role is best characterized as a modular backdoor used to establish and maintain footholds on compromised Windows systems while enabling follow-on collection and post-compromise activity.

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THREAT ACTORS

Groups observed using it

3 distinct threat actors attributed by public researchers. Open in Mallory to see the full evidence chain and overlapping campaigns.

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Naikon

In the same series of attacks, the Naikon threat actors also delivered first-stage malware known as RainyDay or FoundCore used to deploy second-stage payloads and tools used for various purposes, including the Nebulae backdoor.

via bleeping computerbleepingcomputer.com

Lotus Blossom

The new variant's features overlap with both the RainyDay and Turian backdoors...

via the hacker newsthehackernews.com

Firefly

Rainyday: A backdoor associated with the Firefly group (aka Naikon).

via symantec blogsecurity.com

MITRE ATT&CK

Techniques & procedures

26 distinct techniques documented for this family, organized by ATT&CK tactic.

Execution

5 techniques

T1053.005Scheduled TaskEvidence2

The content repeatedly describes malware and threat actors creating, modifying, or invoking Windows scheduled tasks via Task Scheduler or schtasks for persistence, execution, and lateral movement.

T1059Command and Scripting InterpreterEvidence1

Besides deploying additional payloads on compromised systems, attackers can also send RainyDay commands over TCP or HTTP to ... access a command shell...

T1059.003Windows Command ShellEvidence3

The content repeatedly describes threat actors and malware using cmd.exe, the Windows command shell, to execute commands, launch payloads, run batch files, and automate actions on compromised hosts.

T1106Native APIEvidence1

The content is a MITRE ATT&CK-style listing of many malware families and threat groups using Windows/native OS APIs for execution, injection, discovery, anti-debugging, and other actions, ending with 'NtCreateProcess' and 'fork()'.

T1574.001DLLEvidence1

During attacks observed between June 2019 and March 2021, Naikon dropped malicious payloads using side-loading and DLL hijacking vulnerabilities impacting: Sandboxie COM Services ... Outlook Item Finder ... VirusScan On-Demand Scan Task Properties ...

Persistence

1 technique

T1053.005Scheduled TaskEvidence2

The content repeatedly describes malware and threat actors creating, modifying, or invoking Windows scheduled tasks via Task Scheduler or schtasks for persistence, execution, and lateral movement.

Privilege Escalation

1 technique

T1053.005Scheduled TaskEvidence2

The content repeatedly describes malware and threat actors creating, modifying, or invoking Windows scheduled tasks via Task Scheduler or schtasks for persistence, execution, and lateral movement.

Stealth

7 techniques

T1027Obfuscated Files or InformationEvidence1

The content repeatedly describes payloads, strings, configuration files, scripts, URLs, and binaries being obfuscated or encoded using Base64, XOR, RC4, AES, RSA, hex encoding, custom algorithms, and other methods across many malware families and threat actors.

T1027.013Encrypted/Encoded FileEvidence1

Examples throughout the content include 'encrypted payloads decrypted and executed in memory,' 'encrypts its configuration file,' 'AES-encrypted resource,' 'RC4 encrypted embedded scripts,' and 'payload includes an encrypted main component.'

T1036MasqueradingEvidence2

actors used the following command to rename one of their tools to a benign file name: ren "%temp%\upload" audiodg.exe ... APT1 ... used ... AcroRD32.exe ... as a name for malware ... APT28 ... changed extensions on files containing exfiltrated data to make them appear benign ... APT32 has renamed a NetCat binary to kb-10233.exe to masquerade as a Windows update.

T1036.005Match Legitimate Resource Name or LocationEvidence1

Akira has used legitimate names and locations for files to evade defenses.

T1070.004File DeletionEvidence4

The content repeatedly describes malware and threat actors deleting files, directories, droppers, logs, scripts, temporary files, exfiltrated archives, and uninstalling themselves to cover tracks or reduce forensic artifacts.

T1140Deobfuscate/Decode Files or InformationEvidence3

The content is a long ATT&CK-style listing of malware and threat groups that 'decrypt', 'decode', 'deobfuscate', 'unpack', or 'decompress' payloads, strings, configuration data, shellcode, and files prior to execution or use.

T1574.001DLLEvidence1

Credential Access

3 techniques

T1003OS Credential DumpingEvidence1

Using the RainyDay backdoor, the actors performed reconnaissance, uploaded its reverse proxy tools and scanners, executed the password dump tools...

T1555Credentials from Password StoresEvidence1

Agent Tesla can gather credentials from a number of browsers... APT33 has used a variety of publicly available tools like LaZagne to gather credentials... TrickBot can obtain passwords stored in files from web browsers such as Chrome, Firefox, Internet Explorer, and Microsoft Edge... SELECT action_url, username_value, password_value FROM logins; CryptUnprotectData

T1555.003Credentials from Web BrowsersEvidence3

Agent Tesla can gather credentials from a number of browsers... APT3 has used tools to dump passwords from browsers... APT41 used BrowserGhost, a tool designed to obtain credentials from browsers, to retrieve information from password stores... TrickBot can obtain passwords stored in files from web browsers such as Chrome, Firefox, Internet Explorer, and Microsoft Edge

Discovery

2 techniques

T1057Process DiscoveryEvidence3

Tasklist can be used to discover processes running on a system. Numerous malware families and threat groups are described as listing running processes, collecting PIDs, checking for specific process names, or enumerating loaded modules.

T1083File and Directory DiscoveryEvidence4

Carberp has used the NtQueryDirectoryFile and ZwQueryDirectoryFile functions to hide files and directories.

Collection

3 techniques

T1005Data from Local SystemEvidence4

Andariel has collected large numbers of files from compromised network systems for later extraction... APT28 has retrieved internal documents from machines inside victim environments... BADNEWS crawls the victim's local drives and collects documents... many listed groups and malware collect files, documents, credentials, payment card data, or other information from compromised hosts.

T1074Data StagedEvidence1

The content repeatedly describes adversaries and malware storing collected data, command output, credentials, archives, or files in local temporary folders, working directories, hidden directories, registry locations, recycle bins, or specific files prior to exfiltration.

T1113Screen CaptureEvidence2

The content is a MITRE ATT&CK-style listing of malware and threat actors that "can capture screenshots," "take screenshots," "perform screen captures," or "watch the victim's screen." It ends with references to "CopyFromScreen" and "xwd."

Command and Control

7 techniques

T1008Fallback ChannelsEvidence1

APT41 used the Steam community page as a fallback mechanism for C2. Bazar has the ability to use an alternative C2 server if the primary server fails. BISCUIT malware contains a secondary fallback command and control server that is contacted after the primary command and control server.

T1071Application Layer ProtocolEvidence1

attackers can also send RainyDay commands over TCP or HTTP...

T1071.001Web ProtocolsEvidence4

The content is a long ATT&CK-style listing showing numerous malware families and threat groups that 'use HTTP,' 'use HTTPS,' 'HTTP POST requests,' 'HTTP GET requests,' or 'HTTP/S' for command and control communications.

T1090ProxyEvidence1

Using the RainyDay backdoor, the actors performed reconnaissance, uploaded its reverse proxy tools and scanners...

T1095Non-Application Layer ProtocolEvidence1

RainyDay has the ability to switch between TCP and HTTP for C2 if one method is not working. Mis-Type first attempts to use a Base64-encoded network protocol over a raw TCP socket for C2. NETEAGLE will send beacons via UDP/6000 if no proxy is configured.

T1105Ingress Tool TransferEvidence2

The content repeatedly describes malware and threat actors that can "download files from C2," "download additional payloads," "upload and download files," "retrieve payloads from the C2 server," and "copy files to remote machines."

T1573Encrypted ChannelEvidence1

The content is a catalog of malware and threat groups that encrypt command-and-control communications using algorithms such as DES, AES, RC4, XOR, Blowfish, RSA, Camellia, RC2, RC6, and custom ciphers.

ACTIVITY FEED

Recent activity

48 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.

48 SOURCESView more in app

the hacker newsNews

Sep 27, 2025

China-Linked PlugX and Bookworm Malware Attacks Target Asian Telecom and ASEAN Networks

Backdoor whose configuration structure is reused by the described PlugX variant; delivered via DLL side-loading and executed in-memory in the described attack chain.

mitre attack websiteNews

Oct 21, 2021

Updates - Updates - October 2021 | MITRE ATT&CK®

Enterprise New Software: ... RainyDay

mitre attack websiteNews

Oct 21, 2021

Encrypted Channel: Symmetric Cryptography, Sub-technique T1573.001 - Enterprise | MITRE ATT&CK®

Backdoor that can encrypt C2 communications with RC4.

mitre attack websiteNews

Oct 21, 2021

Native API, Technique T1106 - Enterprise | MITRE ATT&CK®

Malware/tool that uses native APIs such as ReadDirectoryChangeW for folder monitoring and file collection.

+44 more in the timeline

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IOC matching

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Threat actor attribution3

Named campaigns wielding this family, with evidence pinned to each claim.

Exploited vulnerabilities

CVEs this family uses for access and lateral movement.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

MITRE ATT&CK mapping26

Every documented technique, ranked by evidence weight.

Researcher chatter

Reddit, Mastodon, and CTI community discussion around this family.

RainyDay