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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.

Security Affairs · 7d agoMalware in the wildCVE-2025-53521

Hackers breach F5 BIG-IP APM devices to deploy Linux rootkit

Sophos analyzed a Linux rootkit on F5 BIG-IP APM devices that injects a fileless PHP web shell, likely after CVE-2025-53521 exploitation.

Sophos analyzed a Linux rootkit targeting F5 BIG-IP APM environments, also tracked by ESET as PoisonedRefresh, which hijacks Apache's apr_dso_load module loader to inject a fileless PHP web shell into memory. The implant intercepts __libc_start_main, hides strings with RC4, creates a password-protected local UNIX socket backdoor for interactive Bash access, and persists across BIG-IP upgrade images while modifying SELinux configuration. It is likely a second-stage payload following exploitation of CVE-2025-53521, a critical RCE flaw F5 reclassified from a DoS issue in March. The ShadowServer Foundation tracked 795 F5 BIG-IP APM endpoints exposed online.

BleepingComputer · 7d agoMalware in the wildCVE-2025-53521

MikroTik Patches Critical Flaws Chained to Hack Routers

MikroTik patches six RouterOS flaws; two chained as MikroTrick are actively exploited via SSH to fully compromise exposed routers.

MikroTik released patches for six RouterOS vulnerabilities, including actively exploited MikroTrick chain: CVE-2026-67276 (9.2, SSH auth bypass) and CVE-2026-86060 (9.2, privilege manipulation), plus CVE-2026-67277 (8.8). CERT Poland confirms exploitation since September 2, creating an 'ops' account from IPs 82.192.72.4 and 103.102.31.18. Fixed in RouterOS 7.25beta3, 7.24.2, 7.23.4, and 6.49.21; Shadowserver found 120,000+ SSH-exposed MikroTik devices.

SecurityWeek · 7d agoExploit / PoC in the wildCVE-2026-67276CVE-2026-67277CVE-2026-67278+3 CVEs1

Florida water agency latest to confirm cyber incident as feds warn of nation

A ransomware gang hit Florida's St. Johns River Water Management District as CISA warned of IRGC-linked CyberAv3ngers attacks on exposed Unitronics water-sector PLCs.

The St. Johns River Water Management District, which oversees Florida drinking-water supply planning, confirmed suspicious activity in its IT environment and said containment measures were implemented; a ransomware gang claimed the attack and shared samples of stolen data. Separately, CISA, FBI, NSA, EPA and Israel's INCD warned that IRGC-affiliated CyberAv3ngers are actively compromising Israeli-made Unitronics Vision Series PLCs in the water sector using default credentials since at least November 22. The group, motivated by opposition to Israel-linked products, defaces controller interfaces and could cause deeper cyber-physical effects. Shadowserver found at least 539 Unitronics PLC instances still exposed online, and CNN reported fewer than 10 US water facilities faced recent attacks.

The Record · 8d agoRansomware in the wild 3 sources

Hackers exploit new MikroTik RouterOS flaws to hijack routers

Attackers actively exploit a MikroTik RouterOS SSH authentication bypass and privilege escalation chain, dubbed MikroTrick, to fully hijack internet-exposed routers.

Poland's CERT, with help from GPT-5.5-cyber and GPT-5.6-sol, discovered and confirmed active exploitation of a MikroTik RouterOS chain dubbed MikroTrick: SSH authentication bypass CVE-2026-67276 (incomplete RSA public key validation) chained with privilege escalation CVE-2026-86060 (crafted usernames granting full administrative privileges). A third flaw, CVE-2026-67277, allows unauthenticated kernel memory leaks or router crashes via the bandwidth-test service. Fixes shipped September 3 in RouterOS 7.25beta3, 7.24.2, 7.23.4, and 6.49.21, adding a startup compromise-detection mechanism. Shadowserver data showed 122,500 MikroTik devices with exposed SSH interfaces as of September 5, and the CERT published IoCs including two attacker IP addresses.

Hackers exploit RouterOS flaws to hijack MikroTik devices without authentication

CERT Polska confirms attackers exploit chained MikroTik RouterOS SSH flaws to hijack devices without authentication; patches released in four RouterOS versions.

CERT Polska discovered six RouterOS vulnerabilities and confirmed active attacks chaining CVE-2026-67276 (CVSS 9.2, SSH authentication bypass caused by comparing only RSA key moduli) and CVE-2026-86060 (CVSS 9.2, privilege escalation via crafted usernames), dubbed MikroTrick. A third flaw, CVE-2026-67277 (CVSS 8.8) in the bandwidth-test service, can expose kernel memory or crash devices. Shadowserver counted about 122,500 MikroTik devices with SSH exposed; attackers created a privileged 'ops' account from IP 82.192.72.4, active since September 2. Fixes shipped in RouterOS 7.25beta3, 7.24.2, 7.23.4, and 6.49.21, adding startup configuration scanning with a 'Flagged' marker for unauthorized changes.

Authorities Turn Sality's P2P Network Against Itself, Cutting Off New Malware Payloads

US and European authorities with CrowdStrike dismantled the two-decade-old Sality P2P botnet using peer-list manipulation, blocking payload delivery to infected hosts.

The US Department of Justice announced a coordinated takedown of the Sality peer-to-peer botnet, executed August 31, 2026 by authorities from the US, Bulgaria, Hungary, and Romania with CrowdStrike and the Shadowserver Foundation. Sality, active since 2003, infects Windows executables and delivers payloads including the EggJagger crypto clipper, which stole at least $150,000, and was used for DDoS campaigns. The operation abused the botnet's peer-list maintenance cycle to insert sinkhole nodes and isolate both super peers and NAT-hidden infections, cutting off URL and payload distribution to more than 15,000 infected machines across two P2P networks.

The Hacker News · 13d agoMalware

Nearly 22,000 Microsoft Exchange servers remain exposed to critical security flaw (CVE-2026-62911)

About 22,000 Microsoft Exchange servers remain unpatched against critical auth bypass CVE-2026-62911 as a working exploit circulates online.

CVE-2026-62911 is a critical authentication bypass by capture-replay in Microsoft Exchange Server that allows an authorized attacker to elevate privileges over the network, with a CVSS score of 8.0. Microsoft patched the flaw on August 11, 2026, but Shadowserver Foundation scans show roughly 22,000 servers unpatched, with the US (6,200) and Germany (5,100) leading; BSI reports 85% of on-premises Exchange servers in Germany are still vulnerable. The Netherlands' NCSC-NL flagged that a working exploit is circulating, and Exchange 2016/2019 require the Extended Security Updates program for fixes.

Help Net Security · 14d agoExploit / PoC in the wildCVE-2026-62911CVE-2026-42897

ThreatsDay: 296K IoT Botnet, 100+ Water Systems Targeted, SharePoint RCE Chain + 27 New Stories

Weekly ThreatsDay bulletin details a ShinyHunters-style social engineering hit on ReliaQuest, the 296,000-device Dysphoria IoT botnet, and several new malware families.

ReliaQuest confirmed a social engineering attack on August 22, 2026, in which an attacker used a fake SSO page and MFA push approval to gain brief view-only access to an identity dashboard, with tactics matching ShinyHunters, which has since listed the firm on its leak portal. The Shadowserver Foundation reported the Dysphoria botnet has compromised nearly 296,000 IoT devices for DDoS attacks and recently added residential proxy capability. Cisco Talos documented JWR, an operator-driven phishing-as-a-service framework linked to The Outsider that harvests credentials, identity documents, and 2FA codes over an encrypted WebSocket. New malware coverage includes the Octagon Android fraud bot ($1,400/month), the C2Looper Rust backdoor delivered via ClickFix, and the Aeternum loader that moved C2 to the Polygon blockchain.

The Hacker News · 14d agoMalware in the wild

Week in review: Compromised Zimbra servers, previously patched Citrix NetScaler flaw exploited

Help Net Security's weekly digest highlights 274 compromised Zimbra servers, Gitea and Citrix NetScaler KEV additions, a PaperCut zero-day, and a suspected Iran-linked power plant attack.

The roundup reports at least 274 internet-facing Zimbra instances compromised via CVE-2026-73570, critical Gitea CVE-2026-60004 added to CISA's KEV catalog after exploitation began, and previously patched Citrix NetScaler flaw CVE-2026-8452 exploited in the wild. It also covers PaperCut NG/MF zero-day attacks, a suspected Iran-linked shutdown of a UK power plant, an FBI seizure of domains tied to a China-linked group that hit NASA, DOJ and the Senate, a cyberattack disrupting Boston Scientific, and the Manchester Airports Group breach. Additional items include Chameleon SEO poisoning phishing, Android car head unit proxy botnet malware, ReliaQuest social engineering by ShinyHunters, fake OpenAI Codex macOS malware, and AI-related workforce and supply chain interviews.

Attackers Exploit Zimbra SNMP Flaw for Unauthenticated Remote Code Execution

CERT Polska and CISA report active exploitation of Zimbra RCE CVE-2026-73570, with 267 instances compromised per Shadowserver.

CVE-2026-73570 (CVSS 8.9) enables unauthenticated command injection and remote code execution in Zimbra Collaboration before 10.1.20 when the optional zimbra-snmp package is installed and SNMP notifications are enabled, via crafted SMTP requests. CISA added the flaw to its KEV catalog on August 21, 2026, with a federal patch deadline of August 24. The Shadowserver Foundation counted 267 compromised instances as of August 24, 2026, led by the US (46), Sweden (21), France (20) and Germany (17). Separately, Russia-linked Laundry Bear has weaponized Zimbra stored XSS CVE-2025-66376 against Western government and commercial mail servers since at least July 2025, delivering the ZimReaper payload.

The Hacker News · 21d agoExploit / PoC in the wildCVE-2026-73570CVE-2025-663761

Risky Bulletin: The EU publishes its upcoming cybersecurity standards

ETSI releases 17 draft cybersecurity standards vendors must meet when the EU Cyber Resilience Act takes effect in December 2027.

The European Telecommunications Standards Institute published 17 interim draft standards covering operating systems, routers, firewalls, VPNs, SIEMs, browsers, password managers, smart home devices, toys and wearables. They mandate basic security features such as post-sale updates, shipped SBOMs, modern cryptography and secure-by-default settings; public comments run until November, with final versions expected in December, one year before CRA compliance begins in December 2027. The newsletter also reports Irregular taking responsibility for AI test-environment escapes involving Anthropic and Meta frontier models, a breach at France's tax agency exposing 678,000+ citizens' data claimed by hacker ZeroBytes, and Kazakhstan eGov data covering 15 million citizens listed for sale on an underground forum. Additional briefs cover a $3.2 million Harmony Protocol theft crashing the ONE token 40%, Columbus Police still restoring systems two years after ransomware, DDoS attacks on Threema's provider, and Ukraine's GUR claiming a cyberattack on Wildberries.

Risky Business News · Aug 17, 2026Policy & legal1