Colt Cyberattack: Multi-Day Outages After WarLock Ransomware Exploited SharePoint Zero-Day

Colt Technology Services, a major UK-based telecommunications provider with operations in over 40 countries, has confirmed that the WarLock ransomware group is behind the cyberattack that struck its systems on August 12, 2025. The attack caused multi-day outages across Colt’s hosting, porting, Voice API, and customer support services, while sparing its core network infrastructure. Initially dismissed as a “technical issue,” Colt later acknowledged it was a cyberattack, taking critical systems offline to contain the threat and engaging with cybersecurity experts and authorities.

A WarLock affiliate has since claimed responsibility, posting samples of 400,000 stolen documents and offering one million records for $200,000. The leaked files reportedly include financial records, employee and customer data, executive communications, and software development materials. WarLock, a ransomware-as-a-service (RaaS) group that emerged in mid-2025, has quickly become one of the fastest-growing extortion outfits. Its methods resemble those of legacy groups like Black Basta, employing double-extortion tactics: rapid disruption via limited encryption, followed by data theft and leaks to coerce ransom payments.

Cybersecurity experts, including Kevin Beaumont, suggest that WarLock gained access through a critical Microsoft SharePoint zero-day vulnerability (CVE-2025-53770). This flaw, part of the larger ToolShell exploit chain, has already been linked to compromises of over 400 organizations worldwide. Once inside, attackers reportedly used web shells, credential theft tools like Mimikatz, lateral movement utilities (PsExec, Impacket), and persistence mechanisms to entrench themselves before deploying ransomware payloads.

The Colt incident underscores several pressing challenges in today’s cyber landscape:

• Exploited Zero-Days: The breach highlights the devastating impact of unpatched enterprise software, especially widely deployed platforms like SharePoint.
• Critical Infrastructure Risks: As a telecom provider, Colt’s disruption demonstrates the ripple effect ransomware can have on essential services.
• Rising RaaS Ecosystems: Groups like WarLock represent a new wave of ransomware collectives—nimble, affiliate-driven, and quick to capitalize on vulnerabilities.
• Global Trend: The attack comes amid heightened concern over OT and telecom security, with CISA reporting an 87% increase in attacks on critical infrastructure this year alone.

For organizations, the key lessons are clear: prioritize timely patching, strengthen incident response playbooks, prepare for data exfiltration risks, and recognize that modern ransomware operations combine technical exploits with psychological pressure campaigns. Colt’s prolonged outages serve as a cautionary tale for enterprises everywhere—security gaps in third-party and enterprise systems remain prime targets for highly motivated threat actors.

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