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AtomSilo is a ransomware operation and malware family that emerged in 2021 and is known for double-extortion attacks combining file encryption with theft of victim data and threats to publish it on a leak site. The group has been referred to as AtomSilo, atomsilo, and atom_silo. AtomSilo intrusions have been observed beginning with exploitation of vulnerable internet-facing Atlassian Confluence servers. After initial access, operators established persistence using DLL sideloading with a legitimate signed executable to load a malicious backdoor, then used WMI-based remote execution and compromised administrative accounts to move laterally across Windows environments. In observed incidents, the actors conducted hands-on-keyboard activity over RDP, performed discovery against servers and security logs, exfiltrated data with Rclone to cloud storage, and then staged ransomware deployment through domain controllers and Group Policy. The operation has also used defense-evasion techniques associated with vulnerable-driver abuse to interfere with endpoint protection before encryption. In one documented intrusion, attack tooling installed a kernel driver via BYOVD-style techniques and propagated payloads through enterprise administration mechanisms to maximize impact. The AtomSilo ransomware payload is a 64-bit Windows executable packed with a modified UPX packer. It enumerates drives, excludes selected system folders, filenames, and extensions from encryption, appends the .atomsilo extension to encrypted files, and drops ransom notes in affected directories. Its encryption routine has been described as chunk-based and similar to LockFile, using XOR followed by AES operations and appending encrypted keying material to the end of affected files. AtomSilo operates a leak site and has publicly claimed restrictions on targeting certain sectors, but it has nonetheless been associated with data theft and publication of stolen information from at least one Brazilian pharmaceutical victim. Reporting in 2026 indicated the operation had resumed activity and disclosed a new victim. Overall, AtomSilo is best characterized as a financially motivated ransomware actor focused on enterprise compromise, data exfiltration, broad Windows-domain deployment, and double-extortion pressure.
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Who, where, and (when attributed) which flag flies behind the operation. Pulled from open-source reporting and Mallory's analyst review.
Sectors the actor has been observed targeting.
Geographies tied to known operations.
23 distinct techniques observed across reporting, grouped by tactic. Hover any cell for the evidence excerpt; click through for MITRE's full description.
3 indicators attributed to this actor: domains, IPs, hashes, and other artifacts pulled from reporting. View more in app.
4 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
Named as one of multiple ransomware groups operating data leak sites and listing fresh victims.
Ransomware group reported as resuming activity and publicly disclosing a new victim (consistent with leak-site/double-extortion style operations).
Conducting ransomware attacks, including data exfiltration and file encryption, after exploiting an Atlassian Confluence vulnerability for initial access and using stealthy backdoors, DLL sideloading, WMI-based lateral movement, RDP hands-on-keyboard activity, RClone for exfiltration, and a kernel driver utility to disable endpoint protection before deploying ransomware.
Ransomware operators conducting double-extortion attacks, including data exfiltration and publication of stolen data, with observed initial access via exploitation of an Atlassian Confluence vulnerability followed by DLL side-loading, WMI-based command execution, use of compromised administrative accounts, and deployment of AtomSilo ransomware.
Match sector + geo + tech-stack targeting against your real footprint.
Every observed MITRE ATT&CK technique, grouped by tactic.
Families this actor is known to deploy, with IOCs and behavior.
CVEs this actor has used in known campaigns.
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Domains, IPs, and hashes tied to this actor, refreshed continuously.