1 malware familyExploits CVEs in the wild

UNC4857

Also known asunc4857

UNC4857 is a temporary cluster designation that was later merged into FIN11 based on overlaps in targeting, infrastructure, certificates, and data leak site usage. Activity initially tracked as UNC4857 included exploitation of the MOVEit Transfer zero-day vulnerability CVE-2023-34362 for data theft. Following the merge, this activity is best understood as part of FIN11’s operations. FIN11 is a financially motivated threat actor known for intrusion activity focused on monetization, including large-scale theft of victim data and extortion-related operations. In the MOVEit campaign, the actor exploited a zero-day vulnerability in a widely deployed managed file transfer product to steal data from affected organizations. This operation demonstrated rapid weaponization of newly disclosed vulnerabilities and an emphasis on post-compromise data exfiltration rather than traditional espionage objectives. Because UNC4857 was subsumed into FIN11, UNC4857 should not generally be treated as a distinct long-term actor. Security practitioners are more likely to encounter this activity under the FIN11 name.

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MITRE ATT&CK

Tradecraft

8 distinct techniques observed across reporting, grouped by tactic. Hover any cell for the evidence excerpt; click through for MITRE's full description.

7 of 15 tactics11 techniques×N= number of intelligence reports citing this technique

MITRE ATT&CK

TA0001

Initial Access

1 technique

T1190×2

Exploit Public-Facing Application

TA0003

Persistence

3 techniques

T1098

Account Manipulation

T1136

Create Account

T1505

Server Software Component

T1505.003

Web Shell

TA0004

Privilege Escalation

1 technique

T1098

Account Manipulation

TA0005

Stealth

1 technique

T1036

Masquerading

TA0006

Credential Access

1 technique

T1555

Credentials from Password Stores

TA0011

Command and Control

1 technique

T1071

Application Layer Protocol

T1071.001

Web Protocols

TA0010

Exfiltration

1 technique

T1041

Exfiltration Over C2 Channel

ARSENAL

Associated malware families

1 malware family attributed to this actor across reporting.

FamilyContextEvidenceLast seen

LemurlootFollowing exploitation of the vulnerability, the threat actors are deploying a newly discovered LEMURLOOT web shell with filenames that masquerade as human.aspx... LEMURLOOT provides functionality tailored to execute on a system running MOVEit Transfer software...1Mar 8, 2026

WEAPONIZED

Associated vulnerabilities

1 CVE this actor has used in observed campaigns. 1 of them exploited in the wild.

CVE-2023-34362SQL Injection in Progress MOVEit TransferIn the wildEvidence2

Mandiant has observed wide exploitation of a zero-day vulnerability in the MOVEit Transfer secure managed file transfer software... assigned CVE-2023-34362... earliest evidence of exploitation occurred on May 27, 2023 resulting in deployment of web shells and data theft.

ACTIVITY FEED

Recent activity

1 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

1 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

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Target overlap

Match sector + geo + tech-stack targeting against your real footprint.

Tradecraft mapping8

Every observed MITRE ATT&CK technique, grouped by tactic.

Malware arsenal1

Families this actor is known to deploy, with IOCs and behavior.

Exploited CVEs1

CVEs this actor has used in known campaigns.

Detection signatures

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

Observables

Domains, IPs, and hashes tied to this actor, refreshed continuously.

UNC4857

Also known asunc4857