Threat actors have begun to actively exploit a recently patched critical security flaw in Broadcom VMware vCenter, according to new findings from QUIRSO.
The vulnerability in question is CVE-2026-59310 (CVSS score: 9.8), a directory-traversal vulnerability in the VMware vCenter server that a malicious actor with network access can exploit to execute arbitrary code. Patches for the flaw were released by Broadcom late last month.
The German cybersecurity company said it discovered the activity following an incident response engagement. The attack chain is said to have exhibited path traversal activity consistent with the flaw, followed by the deployment of a malicious cron job to establish persistence on the host using reverse_ssh, an open-source tool used for setting up SSH connections to threat actor-controlled infrastructure.
Compromised systems identified by QUIRSO were found to first establish contact with the attacker’s domains on August 3, five days after Broadcom publicly disclosed the flaw. In all, there are as many as 361 unique victim IP addresses located across 47 countries. Most of them are located in Germany, the U.S., Turkey, Iran, and France.
“While the attacker might have had prior knowledge of the vulnerability, the strong correlation between the time of disclosure and exploitation suggests the disclosure as the initial starting point for the campaign,” QUIRSO added.
It’s not clear who is behind the exploitation campaign, but it’s believed to be the work of a suspected advanced persistent threat (APT) actor.
It’s worth pointing out that VMware appliances have been a lucrative target for Chinese threat actors like UNC5174, who have weaponized security flaws impacting VMware Tools and VMware vCenter in various espionage campaigns.
In April 2025, SentinelOne disclosed details of a China-nexus threat cluster dubbed PurpleHaze that targeted a South Asian government supporting entity with a Windows backdoor called GoReShell, which uses functionalities from the reverse_ssh tool to establish reverse SSH connections to attacker-controlled hosts.
The use of reverse_ssh is notable as it allows the attacker to establish an outbound connection to an endpoint under their control, effectively bypassing security controls designed to prevent suspicious inbound requests.
“The presence of reverse_ssh should not, by itself, be treated as proof of malicious activity,” QUIRSO noted. “In combination with unauthorized installation, unexpected outbound connections or execution on a vulnerable vCenter appliance, however, it is a high-priority indicator requiring investigation.”
The disclosure comes as Defused Cyber said it’s observing a spike in scanning against VMware vCenter that is indicative of potential exploitation efforts targeting CVE-2026-59309 (CVSS score: 9.8).
“Our honeypots are logging increased fingerprinting – such as version probes via POST /sdk/ (RetrieveServiceContent) and walks of the /websso SAML SSO flow – coinciding with Broadcom’s VMSA-2026-0006 (CVE-2026-59309, unauth auth-bypass in vmdir, CVSS 9.8),” the cybersecurity company said.
Denis Szadkowski, COO and co-founder of QUIRSO GmbH, told The Hacker News that there is not enough evidence at this stage to correlate exploitation and scanning efforts using CVE-2026-59309 with the intrusion set or the attacker infrastructure associated with CVE-2026-59310.
“What we can say with much higher confidence is that the activity we investigated represents a successful compromise rather than merely exploitation attempts, and the forensic evidence strongly points toward CVE-2026-59310 as the initial access vector,” Szadkowski added.
