Armory Castle exploited CVE-2026-102764 for initial access, deployed custom tools, and deleted logs and artifacts.

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Suspected Chinese hackers with a proven knack for exploiting zero-days in security products are at it again, targeting BeyondTrust customers in attacks that researchers have traced back to late August. 

Mandiant researchers said a likely Chinese government-backed espionage group it previously tracked as UNC5221, and now calls Armory Castle, exploited the critical defect — CVE-2026-102764 — then showcased multiple tactics to escalate privileges, hop around the compromised network and evade detection. 

The same threat group has repeatedly exploited a series of defects in Ivanti products since 2023, a Citrix NetScaler zero-day widely known as CitrixBleed, and last year’s Brickstorm campaign that had an average dwell time of 400 days — all resulting in sweeping attack sprees.

“We are aware of only a small number of impacted organizations at this time, but given the stealth of the activity, and the use of a zero-day, it is possible that additional organizations were also compromised prior to the disclosure,” Kelli Vanderlee, senior analyst at Google Threat Intelligence Group, said in an email.

Mandiant warned organizations to “prepare for potential widespread exploitation,” adding that Armory Castle and other threat groups previously conducted broad, opportunistic exploitation following public vulnerability disclosures.

Mandiant and GTIG released their analysis of Armory Castle and its latest campaign as BeyondTrust publicly disclosed the vulnerability in its Remote Support product Thursday. The company’s security said it released a patch for the exploited defect for self-hosted customers Oct. 8 and automatically applied the update to cloud-based versions of the product that same day.

BeyondTrust, which conducted its own investigation and coordinated with Mandiant on an investigation involving a self-hosted customer that was compromised, noted Armory Castle’s prowess.

“This threat actor rotates its infrastructure and tooling for every victim, so attribution here rests on behavior. The indicators from one intrusion rarely survive to the next,” the company’s security team wrote in a blog post. “The threat actor has historically demonstrated a high degree of operational security awareness, professional practices, and tradecraft.”

A BeyondTrust spokesperson declined to answer questions about how many customers are already compromised or why it didn’t publicly disclose the actively exploited zero-day sooner, and instead referred back to its security advisory. 

The company said the first known instance of zero-day exploitation occurred Aug. 29, which it detected and contained Sept. 28. 

BeyondTrust also said it detected the malicious activity after zero-days were confirmed to be exploited in another security vendor’s product Sept. 27. That timing matches a round of zero-days Citrix NetScaler disclosed, following nearly two days of rampant worry and unconfirmed rumors. 

BeyondTrust did not say if there is any link or overlap between the attacks targeting Citrix NetScaler, which went undetected for more than three weeks, and its remote access product. 

GTIG researchers said there isn’t enough evidence to assess an overall targeting trend, but encouraged all potentially vulnerable organizations to apply the patch and hunt for pre-disclosure activity. 

The threat group’s previous targets include business-process outsourcers, government, legal services, technology companies and software-as-a-service providers.

“Armory Castle remains one of the most prominent China-nexus threat actors due to its persistent targeting of various edge device technologies, use of zero-day vulnerabilities for widespread exploitation across multiple industries and regions, and its continuously expanding and evolving arsenal of tools,” said Dan Perez, technical lead at GTIG.

“This is a well-established pattern for Armory Castle,” Vanderlee said. “Targeting edge devices, which typically do not support endpoint detection and response (EDR), allows the threat actor to minimize opportunities for detection and maintain stealthy, persistent access to targeted networks.”

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The ransomware-as-a-service group Medusa has adopted fresh tactics to gain access and added hundreds of victims in a little more than a year, according to an updated U.S. government advisory published Tuesday.

The gang is relying on access brokers,compensating them anywhere from $100 to $1 million, with higher prices going to those who work exclusively with Medusa. However, most of the brokers work simultaneously for “multiple variants at the same time,” the advisory from the Cybersecurity and Infrastructure Security Agency, FBI and Health and Human Services Department states in one of the updated portions of the advisory.

Tuesday’s update advisory expands upon aMarch 2025 advisory, drawing on ongoing FBI investigations.nIt includes information on the kinds of software vulnerabilities Medusa has exploited, such as Fortra GoAnywhere and BeyondTrust flaws.

“Medusa actors operate opportunistically by targeting victims with unpatched software rather than focusing on specific organizations or sectors; however, the Healthcare and Public Health (HPH) Sector has been a frequent victim of Medusa operations,” according to the advisory. “Medusa actors leverage newly announced exploits within 24 hours and have been observed to use exploits up to a week before public vulnerability disclosure.’

“However, there is no indication Medusa actors develop their own zero-day or N-day vulnerabilities, preferring instead to obtain advanced access to exploits from unknown sources or to quickly leverage newly announced exploits before potential victims can mitigate vulnerabilities through patching,” the advisory continues.

The approach appears to be netting gains: From March 2025 to April of this year, the victim tally in the advisory jumped from more than 300 to more than 500. The group was first identified in 2021.

“Medusa actors often use legitimate tools and living off the land techniques to evade detection. They may also leverage remote monitoring and management software and remote access services, including Remote Desktop Protocol, for lateral movement,” as updated sections of the advisory detail. “Once inside a network, they use common utilities and tools to support credential access, data exfiltration, and ransomware deployment.”

Earlier this year, Microsoft detailed how a group it dubbed Storm-1175 was making use of Medusa ransomware in speedy operations. Symantec and Carbon Black also detailed earlier this year how North Korean hackers were leaning on Medusa to target the health care sector.

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