Was Kumagai Gumi Group hit by ransomware?

Kumagai Gumi Group was listed by the ALPHV/BlackCat ransomware operation (Japan), and stolen data was published on the group's leak site. Darkfield tracks this disclosure with the original leak post, screenshot and group context.

Who is the ALPHV/BlackCat ransomware group?

ALPHV/BlackCat is a ransomware operator tracked by Darkfield. See the full operator dossier for its known victims, sectors targeted, IOCs and leak-site infrastructure.

What data was leaked in the Kumagai Gumi Group breach?

ALPHV/BlackCat published data attributed to Kumagai Gumi Group. Darkfield captured the leak post and a screenshot of the listing.

Ransomware victim disclosure

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Kumagai Gumi Group

Claimed by ALPHV/BlackCat · listed 2 years ago

28m

Age

since listed · data leaked

Status timeline

ListedMar 1, 2024
Data leakeddate unknown

At a glance

Group: ALPHV/BlackCat
Status: Data leaked
Country: Japan
Sector: Business Services
Listed on leak site: Mar 1, 2024

About the victim

AI dossier — public-source company profile

Kumagai Gumi Co., Ltd. is a Japanese construction company with registered headquarters in Fukui, Fukui Prefecture, and actual head office operations in Shinjuku, Tokyo. The group operates as a significant player in Japan's construction sector.

Industry: Construction
Address: Shinjuku, Tokyo, Japan (head office); Fukui, Fukui Prefecture, Japan (registered headquarters)

Attack summary

Severity: medium — Data has been published by the group (disclosed status: data_published), indicating confirmed exfiltration, but the specific nature, volume, and sensitivity of the data are not detailed in the available post excerpt. Construction companies typically hold business contracts, project data, and employee information; without clarity on what was taken, medium severity is appropriate.

ALPHV claims to have compromised Kumagai Gumi Group and published exfiltrated data. No specific details on data categories or operational impact are provided in the post excerpt.

medium

What the group claims

Kumagai Gumi Co., Ltd. is a Japanese construction company founded in Fukui, Fukui Prefecture, Japan. The company still has registered headquartersin Fukui, but the actual head office is located in Shinjuku, Tokyo

Sources

Source

Indexed 2 years ago

This page surfaces a public ransomware disclosure indexed by Darkfield. Original posts come from the operator's own leak site; we cross-check against ransomware.live, RansomLook and RansomWatch where applicable. Share this URL freely.

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Disclosure context

About ALPHV/BlackCat

ALPHV, also known as BlackCat or Noberus, is a sophisticated ransomware-as-a-service operation that emerged in November 2021 and quickly became one of the most prolific ransomware groups globally, driven by financial motivations and responsible for compromising over 930 victims worldwide. The group is believed to be operated by Russian-speaking cybercriminals and represents an evolution of the BlackMatter ransomware operation, operating under a RaaS model that recruits experienced affiliates from other disbanded ransomware groups. ALPHV employs a multi-faceted attack methodology utilizing various initial access vectors including compromised Remote Desktop Protocol credentials, phishing campaigns, and exploitation of unpatched vulnerabilities, followed by deployment of their Rust-based ransomware payload that supports both Windows and Linux environments, while consistently employing double extortion tactics that involve data theft prior to encryption and threats to publish stolen information on their leak site. Notable campaigns include high-profile attacks against critical infrastructure and major corporations across healthcare, finance, and energy sectors, with the group demanding ransoms ranging from hundreds of thousands to millions of dollars, prompting the FBI and CISA to issue multiple advisories warning of their targeting of critical infrastructure organizations. As of early 2024, ALPHV remains active despite ongoing law enforcement efforts, continuing to evolve their tactics and maintain their position as one of the most significant ransomware threats globally. The group has been linked to 1,662 public disclosures across our corpus. First observed on a leak site on September 9, 2021; most recent post March 3, 2024. The operation is currently inactive.

Also tracked as: ALPHV, BlackCat, Noberus.

Timeline of this disclosure

March 1, 2024Kumagai Gumi Group listed by ALPHV/BlackCaton the group's public leak site

Other recent disclosures by ALPHV/BlackCat

ALPHV/BlackCat has been linked to 1,662 public victims on Darkfield. A sample of the most recent:

See the full ALPHV/BlackCat dossier →

Sector and geography

This disclosure adds to ransomware activity in the Business Services sector, which has 3,796 disclosures indexed across all operators we track. Geographically, Kumagai Gumi Group is reported in Japan, a country with 220 ransomware disclosures in our corpus.

If your organisation is affected

A listing by ALPHV/BlackCat means Kumagai Gumi Group appeared on a ransomware extortion site and data attributed to it has been published. If this is your organisation, or a supplier you depend on, the priority is to confirm the intrusion and contain it before the window to act closes.

Engage your incident-response team and preserve forensic evidence before remediating — do not wipe affected systems first.
Force a password reset and revoke active sessions for exposed accounts; rotate any credentials, API keys or certificates that may have been in the stolen data.
Assess regulatory notification duties (GDPR, NIS2, sector regulators) — many carry a 72-hour reporting clock from awareness.
Report the incident to your national CERT, JPCERT/CC (Japan), as required for your jurisdiction.
Monitor for the data appearing on ALPHV/BlackCat's leak site and across paste and breach channels, and brief downstream partners who may be exposed through you.

How we know this. Darkfield monitors public ransomware leak sites continuously, archiving every new disclosure and the data later released against the victim. Each entry on this page is sourced from the operator's own publication and cross-checked against complementary OSINT feeds (RansomLook, ransomware.live, RansomWatch). We do not collect or host stolen data — only the metadata, timestamps and screenshots needed to make the public disclosure searchable and accountable. Records here are corrected when the original post is edited, retracted, or merged with another disclosure.