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FamousSparrow Exploits Public-Facing Exchange Servers to Deploy SparroWocky Backdoornew
ESET attributes a new SparroWocky backdoor to espionage group FamousSparrow, deployed via exploited internet-facing Exchange servers across Latin American governments.
ESET's Welivesecurity team reports FamousSparrow gained initial access by exploiting publicly reachable Microsoft Exchange servers, with roughly 90 percent of targets since mid-2025 in Latin America, including governments in Argentina, Ecuador, Guatemala, Honduras, Panama, Peru, Puerto Rico, and Venezuela. The group's new modular C-language backdoor SparroWocky replaces SparrowDoor and uses a three-part loader: a legitimate executable, a malicious DLL side-loaded in memory, and an encrypted payload. It persists via Windows services or Registry Run keys, supports screenshots, file operations, TCP proxying, Beacon Object Files, TLS/RC4-encrypted C2, and anti-forensics such as call-stack spoofing. IOCs including loader SHA-1 hashes and C2 IP addresses were published.
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PoisonedRefresh: A Fileless Linux Rootkit That Injects PHP Web Shells Into F5 BIG-IP APM Server Memory
Sophos details PoisonedRefresh, a fileless Linux rootkit that injects a memory-resident PHP web shell into F5 BIG-IP APM after exploitation of CVE-2025-53521.
On September 8, 2026, SophosLabs published an analysis of Linux/Agnt-IC (dubbed PoisonedRefresh by ESET) found in compromised F5 BIG-IP Access Policy Manager environments. Initial access leverages CVE-2025-53521, an unauthenticated RCE in BIG-IP APM when an access policy is configured on a virtual server; F5 confirmed exploitation and links the activity to cluster c05d5254, while Shadowserver observed 795 exposed vulnerable endpoints. A first stage hidden in a modified umount binary modifies /usr/sbin/httpd and SELinux configuration and embeds itself in BIG-IP upgrade images for persistence. The second-stage ELF intercepts __libc_start_main, hooks apr_dso_load, and injects a PHP web shell into libphp memory via mmap manipulation, leaving no disk artifacts, and exposes a /bin/bash shell via a local UNIX domain socket instead of a TCP port.
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