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Redtail Payload Analysis [Guest Diary], (Wed, Sep 9th)
SANS guest analyst detonated a RedTail Linux sample from a DShield honeypot, finding process masquerading as php-fpm, monitoring-kill behavior, and a TCP listener.
A DShield honeypot captured multi-architecture RedTail Linux executables (ARM, ARM64, i686, RISC-V, x86-64) deployed via shell scripts. Dynamic analysis of the UPX-packed, statically linked x86-64 sample (SHA-256 63be5f38...d35e) in an isolated Ubuntu 24.04 VM on Proxmox showed it renamed its process via prctl(PR_SET_NAME), killed a filesystem-monitoring process, and opened a TCP listening socket while surviving processes posed as php-fpm or PostgreSQL-like workers. Differential memory images pre- and post-execution were captured from the hypervisor for forensics.
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The extension you never installed: KREMLIN forges Chrome's own integrity checks to steal banking sessions
Elastic details KREMLIN, a Brazilian banking malware whose malicious Chrome/Edge extension forges Chromium integrity checks to steal sessions.
Elastic Security Labs tracked operation REF9334 and its KREMLIN toolkit, a Brazilian banking malware campaign impersonating twelve banks across seven campaigns since May 2025. The infection chain uses multi-stage obfuscated JavaScript loaders with sandbox checks (file and process counting), scheduled-task persistence, and an Ethereum smart contract acting as a dead-drop resolver for C2 and payload URLs, abusing Archive.org for hosting. The malicious browser extension bypasses Chromium integrity mechanisms by manipulating Secure Preferences and regenerating required HMACs and App-Bound encrypted hashes. Threat Command disrupted over 1,500 infections by registering the kill-switch canary domain.
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Tracking OceanLotus’ new Downloader, KerrDown
Unit 42 identifies KerrDown, a new OceanLotus (APT32) downloader active since 2018 targeting Vietnamese speakers via malicious macros and DLL side-loading.
Unit 42 tracks KerrDown, a previously undocumented downloader family used by OceanLotus (APT32) since at least early 2018, primarily targeting Vietnam or Vietnamese-speaking individuals. Delivery uses macro-laced Microsoft Office documents embedding base64-encoded 32-bit and 64-bit DLLs, and RAR archives containing a legitimate program abused for DLL side-loading. KerrDown is dropped as main_background.png, downloads a DES-encrypted payload from a URL, and executes it directly in memory. Researchers used Jaccard-index similarity analysis to identify the new family, connect campaign samples, and infer patterns in the group's working hours and days.
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Hackers Abuse Google CAPTCHA, WebDAV and BNB Smart Chain to Deploy Credential-Stealing Malware
Cisco Talos details ClickFix campaigns abusing fake Google CAPTCHA prompts, WebDAV and BNB Smart Chain to deploy the Amatera infostealer.
Cisco Talos identified a multi-stage campaign, first observed in April 2026 when a Ukrainian government organization executed a disguised DLL named verification.google from a WebDAV path. The chain combines ClearFake JavaScript injected via malicious Cloudflare Workers, EtherHiding payloads stored in BNB Smart Chain contracts, ClickFix social engineering, and WebDAV-hosted DLL loaders to deliver the Amatera (ACR Stealer) infostealer. The Amatera configuration contained over 400 collection entries targeting browsers, messengers, crypto wallets, password managers, FTP and VPN tools, hunting for .kdbx, .p12, .pfx and .pem files. The pf.ch branch deploys ZigCryptoStealer, an EDR-terminating vulnerable driver and Go-based reverse TCP proxies, while the verification.google branch installs NetSupport Manager, supporting moderate-confidence attribution of the UAT-10820 activity to a Russian actor.
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14 Trojanized npm Packages Drop RedC2 4.0 Linux Backdoor With AI
Trend Micro found 14 trojanized npm calendar utilities delivering RedC2 4.0, an AI-powered cross-platform backdoor sold for $99.99.
Trend Micro's TrendAI identified 14 functional but trojanized npm packages (streak-*, kit-map-vim, map-streak-kit) that load a bundled Linux implant, the RedShell beacon of RedC2 4.0, without requiring install hooks. RedC2 4.0, sold by Red Offsec for $99.99 and advertised on Hack Forums by actor MarlboroMan in June 2026, offers shell access, credential theft, SOCKS5 proxying, in-memory execution, and an LLM-driven component called Red Agent for natural-language post-exploitation. The framework has evolved from version 2.0 in August 2025 through 4.0, with the Linux beacon introduced in the latest release.
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PAPERMILL Malware Campaign Abuses Signed Notepad++ to Deliver VenomRAT to Windows Users
JUMPSEC tracks PAPERMILL, a China-nexus phishing campaign using a signed Notepad++ binary, libcurl.dll sideloading, and Donut loaders to deploy VenomRAT against Indian tax-audit targets.
PAPERMILL delivers ISO disk images via tax-audit phishing emails that passed SPF, DKIM, and DMARC, containing a renamed Authenticode-signed Notepad++ executable and a malicious libcurl.dll that proxies curl functions while executing loader logic in DllMain. The chain uses Mark-of-the-Web bypasses, anti-sandbox sleeps, UAC elevation prompts, Registry persistence, and a Donut shellcode loader to reflectively load .NET VenomRAT v6.0.3 with HVNC and credential-stealing capability, with C2 at 154.36.188.201:4449. JUMPSEC assesses the campaign as China-nexus, financially motivated, and Silver Fox-adjacent rather than definitively Silver Fox-operated.
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KRBanker Targets South Korea Through Adware and Exploit Kits
Unit 42 details KRBanker banking trojan targeting South Korean bank users via KaiXin exploit kit and NEWSPOT adware, using pharming and process hollowing.
KRBanker (aka Blackmoon) is a banking trojan targeting online banking users in the Republic of Korea, with roughly 2,000 unique samples and 200+ pharming servers observed by Unit 42 over six months. It is distributed through the KaiXin exploit kit exploiting Adobe Flash CVE-2014-0569 and CVE-2015-3133, and through the NEWSPOT adware update channel that also delivers the Venik trojan. The trojan uses process hollowing, retrieves pharming server IPs from Qzone profile nickname fields, and abuses Proxy Auto-Config with a local proxy to redirect banking traffic to forged sites.
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PC malware statistics, Q3 2023
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Rogue ScreenConnect Clients Spread Four-Stage VBScript Chain to Newly Connected Hosts
Huntress says rogue ScreenConnect clients spread a four-stage VBScript chain delivering backdoors, privilege-escalation tools, or an XMRig miner to newly connected hosts.
Huntress identified three unrelated August 2026 incidents using a Quick Assist tech-support scam, a phishing-delivered MSI installer, and a fake Geek Squad refund form to install rogue ScreenConnect clients. Each client repeatedly spawned wscript.exe to run 1.vbs through 4.vbs, which profiled the host, enumerated installed security products, and downloaded stage-specific payloads from Dropbox. Depending on detected state, payloads included a user-level ScreenConnect backdoor, UAC-bypass privilege escalation tooling, or tunneling utilities with an XMRig cryptocurrency miner. Infected clients re-infected newly connected hosts, creating worm-like propagation, and ConnectWise issued an advisory about affected file transfer behavior in ScreenConnect.
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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 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.
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Stealth rootkit targeting F5 BIG-IP could expose enterprise identity gateways
Sophos analyzed a stealth Linux rootkit that hides a web shell in memory on compromised F5 BIG-IP APM identity gateways, evading file-based detection.
Sophos analyzed a second-stage Linux rootkit implant found in compromised F5 BIG-IP APM environments running Apache and PHP, linked to exploitation of CVE-2025-53521, an unauthenticated RCE. The implant hooks Apache's PHP-loading process and serves modified in-memory versions of three legitimate webtop PHP files (apm_css.php3, full_wt.php3, webtop_popup_css.php3), leaving on-disk files untouched so hashes and integrity checks pass. It also establishes access via an authenticated local UNIX socket that can provide an interactive /bin/bash session. Experts warn compromised APM appliances, which handle federated SSO and terminate TLS at enterprise perimeters, could enable SSO token theft and lateral movement to trusted downstream applications.
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F5 BIG-IP APM Malware Injects a PHP Web Shell Into Memory, Evading Disk Scans
Sophos found F5 BIG-IP APM malware that injects a PHP web shell into Apache's memory, evading disk scans, linked to exploited CVE-2025-53521.
Sophos's September 7 analysis describes malware tied to F5's c05d5254 activity that hooks apr_dso_load, modifies the libphp PHP module in memory, and injects a PHP web shell when Apache loads apm_css.php3, full_wt.php3 or webtop_popup_css.php3, leaving on-disk files clean. A separate installer infects /usr/sbin/httpd and umount, runs before Apache starts, disables SELinux (per ESET's related PoisonedRefresh analysis), and opens a local socket at /run/bigtlog.pipe for shell access. The activity is linked to CVE-2025-53521 in BIG-IP APM, rated 9.8 CVSS 3.1, patched in October 2025, added to CISA KEV on March 27, 2026.
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Cyclops Blink Evolves Into x86-64 Linux Implant With Packet Sniffing and Internal Network Scanning
Sophos uncovers a new x86-64 Cyclops Blink Linux implant with packet sniffing and internal network scanning on compromised Cisco FMC appliances.
Sophos identified a 64-bit Linux Cyclops Blink implant in August on compromised Cisco Firewall Management Center devices, persisting via SysV init scripts and masquerading as the process 'kworker01'. The modular malware runs five child processes for reconnaissance, file transfer, scanning, packet capture, and persistence, and beacons hourly over outbound TLS to hardcoded C2 89.34.96.56 on ports 43856 and 49172. The family was previously tied to Russian-linked Sandworm activity on WatchGuard appliances, though Sophos treats 2026 attribution cautiously. The packet-capture module applies configurable filters to retain credentials, cookies, and authentication tokens from raw Ethernet traffic.
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