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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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New KATARU IoT Malware Packs Linux Privilege Escalation Exploits and Mirai-Style DDoS Attacks
Nozomi Networks identified KATARU, a new Mirai-style IoT botnet delivered via Telnet brute force that uses Linux privilege-escalation exploits and encrypted C2 for DDoS floods.
Nozomi Networks identified KATARU in August after a Telnet password-guessing attack against a honeypot retrieved an ARM payload. The malware attempts exploits for CVE-2026-46300 (Fragnesia), CVE-2026-43284 (DirtyFrag), and CVE-2026-31431 (Copy Fail), plus a cgroup v1 release_agent escape, and persists via systemd services, cron tasks, rc scripts, OpenWrt hooks, and Android boot locations. Its C2 uses X25519 key exchange with ChaCha20-Poly1305 encryption and supports TCP, UDP, ICMP, HTTP, QUIC, and DNS floods, plus SSH brute forcing and command execution; embedded exploit shellcode in the ARM build targeted x86, suggesting untested copied code.
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Hackers Turn More Than 3,500 Redis Servers Into Cryptocurrency Miners
Hunters.io researchers report 3,562 exposed Redis servers hijacked via replication abuse into Monero cryptomining, causing performance loss and data-integrity risk.
Researchers at Hunters.io exposed a cryptomining operation that compromised 3,562 distinct Redis servers after scanning 12,966 targets. The attackers used unauthenticated Redis instances and master-replica replication to plant a cron task that downloaded and ran XMRig every five minutes. The miner connects to a mining pool over encrypted port 443 and hides among temporary files. Impact includes high CPU usage, elevated cloud bills, and data-loss risk from altered Redis persistence settings.
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WordlistLoader Delivers Amatera via ClickFix, SynkLoader Phishes Windows Passwords
Gen Digital details WordlistLoader delivering Amatera Stealer via ClickFix and EtherHiding, while SynkLoader phishes Windows credentials through Microsoft Teams.
Gen Digital identified WordlistLoader, an intermediate stage that reconstructs shellcode encoded as plain English words (or 16-byte UUID chunks) and loads Amatera Stealer 4.3.3-alpha1, delivered through ClearFake ClickFix prompts on compromised websites. The chain uses EtherHiding to fetch JavaScript from a blockchain smart contract, hidden cmd.exe via conhost, WebDAV-mounted shares with rundll32 execution, and ETW bypass via hardware breakpoints. The stealer adds hardened WoW64 syscalls, Heaven's Gate indirect-syscall trampolines and a redesigned application-bound encryption bypass. Separately, Expel observed SynkLoader distributed via Microsoft Teams phishing impersonating IT service desks, installing an MSI from Azure blob storage and serving a fake lock screen to capture credentials.
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TWINLOOT Abuses SharePoint and Teams to Steal Credentials and Move Across Networks
Ontinue disclosed TWINLOOT, a Python implant hiding C2 in SharePoint dead drops and Teams TURN relays, harvesting credentials and pivoting via reverse SOCKS5.
Ontinue's Cyber Defense Center identified TWINLOOT during a July 2026 campaign investigation: a modular, PyArmor-hardened Python implant (a 39 MB bootstrap-fat.pyc loader) whose entire C2 infrastructure lives inside trusted Microsoft services. Tasking flows through SharePoint Online file dead drops polled every 15 seconds via the Microsoft Graph API, while interactive operator access uses WebRTC DataChannels relayed by Microsoft Teams TURN servers; Graph traffic is driven by the victim's own headless Edge browser. The implant harvests Windows credentials with fake lock screens, offers a reverse SOCKS5 pivot for lateral movement to SMB, RDP, WinRM, and MSSQL, executes commands, and persists on hosts. Initial access is assessed to be Teams social engineering masquerading as IT support, prompting a PowerShell command to download the payload.
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