Description

PEERSTITCH is an ARM64-based, memory-resident implant identified in an extended cyber intrusion targeting a telecommunications managed service provider’s FortiGate firewall infrastructure. Published on October 14, the investigation attributed the activity to CL-STA-0954, also tracked as UNC5820. The attackers initially exploited CVE-2024-47575, known as FortiJump, to access a centralized FortiManager appliance through TCP port 541. They registered a rogue virtual appliance and exfiltrated a configuration archive containing network details, administrative databases, encrypted credentials, certificates, and private keys associated with more than 500 managed firewalls. Researchers confirmed that administrative and SSL/VPN passwords could be recovered. Stolen credentials were subsequently used to establish unauthorized VPN sessions and configure packet captures to collect sensitive traffic and support internal reconnaissance. The attackers later deployed PEERSTITCH by exploiting CVE-2025-61624, a privileged path-traversal vulnerability in Fortinet’s command-line interpreter. By manipulating unsanitized system.auto-script object names, they escaped designated directories and executed a loader with operating-system privileges. The deployment chain staged JavaScript, WebAssembly, and a native ARM64 injector named lldprx. After installation, the injector removed its executable and targeted the legitimate FortiOS processes miglogd and iked. Using ptrace, it inserted malicious code into anonymous memory regions with read, write, and execute permissions, redirecting normal execution through covert hooks. These hooks examined process traffic for specific markers and transferred session identifiers between processes without creating a dedicated listening port or initiating independent outbound connections. Investigators also identified a separate persistence and communication mechanism involving Apache’s mod\_md certificate-management module, whose manipulated ACME configuration enabled an SSH reverse shell through Node.js. Defenders should investigate suspicious executable memory mappings within miglogd and iked, cross-process memory modifications, abnormal auto-script entries, and unexpected logging disruptions. Fortinet identifies FortiOS 7.4.10 and 7.6.5 as fixed releases for CVE-2025-61624. Organizations should patch affected systems and rotate potentially exposed credentials, certificates, and private keys. The investigation did not establish whether downstream customer networks were compromised.