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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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Hackers Disguise CHOSEN BRICK Malware as AI Apps, Antivirus Software and MRI Results
NCSC, FBI, and AIVD warn Iranian state-linked actors deliver CHOSEN BRICK Windows spyware via fake AI apps, antivirus installers, and MRI-result lures.
A joint advisory from the UK NCSC, FBI, and Dutch AIVD details CHOSEN BRICK (FBI tracking name: HEAVYGRAM), Iranian state-linked Windows spyware targeting dissidents, activists, and journalists worldwide since at least 2025. Lures impersonate Pictory, RunwayML, Norton Antivirus, Telegram, Adobe Flash Player, and KeePass, and operators pivot conversations from corporate to personal devices to bypass enterprise controls. The spyware persists via Registry Run keys, adds Microsoft Defender exclusions, uses per-victim Telegram bots for command-and-control, and exfiltrates screenshots, audio, email, and chat data via Telegram and cloud services, with some victim data appearing on pro-Iranian leak sites.
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Hackers deploy Linux rootkit on F5 BIG-IP APM devices, hiding web shell in memory
Sophos analyzed a Linux rootkit, tracked as PoisonedRefresh, on hacked F5 BIG-IP APM devices hiding an in-memory web shell linked to exploited CVE-2025-53521.
Sophos and ESET analyzed an implant (named PoisonedRefresh by ESET) deployed on compromised F5 BIG-IP APM appliances, which serves enterprise, financial, government, and public sector deployments. The second-stage payload intercepts __libc_start_main, hooks Apache's APR module loader (apr_dso_load), RC4-encodes key strings, and rewrites PHP file reads in memory to embed a web shell inside legitimate scripts like apm_css.php3, full_wt.php3, and webtop_popup_css.php3, leaving on-disk files unchanged. A related installer component infects /usr/sbin/httpd, persists across BIG-IP upgrade images, modifies SELinux configuration, and deploys the payload. The malware also creates a Unix domain socket at /run/bigtlog.pipe that hands authenticated local connections to /bin/bash; F5 links the activity to CVE-2025-53521, an unauthenticated RCE in BIG-IP APM already exploited in the wild.
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Hackers Exploit Critical FortiGate Flaw to Deploy AI-Assisted PivotC2 RAT
SOCRadar says attackers exploit FortiGate CVE-2025-25249 to deploy the PivotC2 Node.js RAT, compromising 178 of 30,000 targeted devices and stealing credentials.
SOCRadar's Threat Research Unit reports active exploitation of CVE-2025-25249, a CVSS 9.8 heap-based buffer overflow in the cw_acd daemon of FortiOS and FortiSwitchManager, via crafted CAPWAP requests to UDP port 5246, compromising at least 178 of 30,000 targeted internet-exposed FortiGate devices since July 2026. The campaign deploys PivotC2, a Node.js RAT that provides interactive shells, SOCKS5/HTTP proxying, port forwarding, network scanning, and automated configuration harvesting that decrypts stored FortiGate credentials, including VPN pre-shared keys, SSL-VPN credentials, and LDAP secrets. Russian-language artifacts, AD enumeration, browser credential theft, RDP enablement, and exfiltration of Exchange .pst files to Wasabi S3 point to a Russian-speaking, financially motivated group; two US organizations confirmed full-network intrusions. Fixes include FortiOS 7.6.4/7.4.9/7.2.12/7.0.18+ and FortiSwitchManager 7.2.7/7.0.6+, plus blocking CAPWAP on internet-facing interfaces.
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Dogged Russia-based botnet dismantled after 23-year run
Law enforcement, CrowdStrike and Shadowserver dismantled the 23-year-old Sality P2P botnet that infected more than 11 million devices.
Sality, a Russia-based peer-to-peer botnet active for 23 years and infecting over 11 million devices, was dismantled by law enforcement working with CrowdStrike and the Shadowserver Foundation. CrowdStrike poisoned the botnet's peer list so infected machines permanently disappeared from the operator's view, while domains were seized in a coordinated effort involving the FBI, Justice Department, Europol and authorities from Bulgaria, Hungary and Romania. The financially motivated operation enabled cryptocurrency theft, DDoS attacks and other cyberattacks, and Europol said the effort dates back to 2017; the operators were not named.
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