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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 Actively Exploit Critical WooCommerce Plugin Vulnerability to Upload PHP Backdoors

Attackers actively exploit CVE-2026-27540 (CVSS 9.8) in WooCommerce Wholesale Lead Capture plugin to upload PHP webshells; patch shipped in version 2.0.3.2.

CVE-2026-27540 (CVSS 9.8) in the WooCommerce Wholesale Lead Capture plugin affects versions 2.0.3.1 and earlier across roughly 6,000 active installations. The unauthenticated AJAX handler wwlc_file_upload_handler trusts a client-supplied file_settings allowlist, letting attackers upload shell.php for remote code execution. Wordfence has blocked more than 100,000 exploit attempts since disclosure, with spikes in June, July, and August 2026. The vendor fixed the flaw in version 2.0.3.2.

GBHackersupdated · 5h agofirst · 1d agoExploit / PoC in the wild 6 sourcesCVE-2026-27540

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.

The Hacker News · 7d agoMalware in the wildCVE-2025-53521

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.

CSO Online · 6d 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

Over 440,000 Exploit Attempts Target Super Forms and Elementor Pro RCE Flaws

Wordfence blocked 440,000+ exploit attempts against critical unauthenticated RCE flaws in WordPress plugins Super Forms and Elementor Pro.

Wordfence reports mass exploitation of two unauthenticated arbitrary file upload RCE flaws: CVE-2026-14894 in Super Forms (CVSS 9.8, fixed in 6.3.314) and CVE-2026-32475 in Elementor Pro (CVSS 9.0/9.8, fixed in 4.2.2), with over 250,000 and 190,000 blocked exploit attempts respectively. Attackers upload Base64-encoded PHP web shells such as Mushr00w_upl.php to execute code, create administrator accounts, exfiltrate data, or seize sites. Super Forms exploitation began July 14, 2026 and peaked above 40,000 requests on August 18; Elementor Pro attacks started August 19. Successful Elementor Pro exploitation requires a published page with a Form widget containing a File Upload field.

The Hacker News · 12d agoExploit / PoC in the wildCVE-2026-14894CVE-2026-32475

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.

Help Net Security · 7d agoMalware in the wildCVE-2025-535211

StopAndProtect Uses Nearly 2,000 Hacked WordPress Sites to Spread Malware and Steal Data

Check Point details StopAndProtect: ~2,000 compromised WordPress sites deliver ClickFix fake-CAPTCHA malware toolkit combining ransomware, credential theft, screenshots, and WhatsApp surveillance.

Check Point researcher Jaromír Hořejší reports the campaign begins with ClickFix fake-CAPTCHA prompts that trigger a PowerShell command, then two .NET downloader stages that launch six components: SilentEncryptor, NetworkShareScanner, a VBS spreader, LockScreen, SimpleChatProxy, and SilentDataCollector. Hacked WordPress sites host malware stages, serve C2 commands, and receive exfiltrated logs; the actors installed a self-deleting WordPress plugin enabling arbitrary PHP upload anywhere under the WordPress root. From mid-May to late July 2026 the operators exfiltrated more than 700 archives including screenshots every 30 seconds, keylogger output, and WhatsApp contact data, and opsec failures exposed their Visual Basic automation tooling and lists of nearly 2,000 compromised domains.

The Hacker News · 27d agoThreat actor in the wild

Thai Broadband Provider Hacked via Fortinet Vulnerability

Hackers exploited Fortinet CVE-2024-21762 RCE to breach Thai broadband provider 3BB, deploying MeshCentral backdoors and credential-harvesting tools across its network.

Hunt.io uncovered an intrusion staging directory in Thailand containing 298 files of custom tooling built for Triple T Broadband (3BB) and its former owner Jasmine. Initial access came via fingerprinting a FortiGate SSL-VPN appliance and exploiting CVE-2024-21762 for remote code execution, after probing CVE-2018-13379, CVE-2022-42475, and CVE-2023-27997. The actor also probed F5 BIG-IP for CVE-2021-22986, CVE-2022-1388, and CVE-2023-46747, escalated privileges with PwnKit and Dirty COW, used MeshCentral as a C2 backdoor, harvested SSH/database/SNMP/Radius credentials, deployed PHP web shells, and ran cleanup scripts to hide the intrusion.

SecurityWeek · 1d agoThreat actor in the wildCVE-2018-13379CVE-2022-42475CVE-2023-27997+4 CVEs

Attackers Actively Exploiting Critical Vulnerability in WooCommerce Wholesale Lead Capture Plugin

Attackers are actively exploiting an unauthenticated arbitrary file upload flaw in the WooCommerce Wholesale Lead Capture plugin, enabling PHP backdoors and remote code execution.

A critical unauthenticated arbitrary file upload vulnerability in WooCommerce Wholesale Lead Capture, a premium WordPress plugin with an estimated 6,000 active installations, was publicly disclosed on February 20, 2026. Wordfence reports attackers are now actively exploiting the flaw to upload arbitrary files, including PHP backdoors, and achieve remote code execution. No CVE ID was cited in the report.

Wordfence · 2d agoExploit / PoC in the wild1

Attackers Actively Exploiting Critical Vulnerability in Super Forms Plugin

Attackers are actively exploiting a critical unauthenticated file upload flaw in the Super Forms WordPress plugin to deploy PHP backdoors for RCE.

Wordfence disclosed on July 9, 2026 a critical unauthenticated arbitrary file upload vulnerability in the Super Forms WordPress plugin, which has roughly 13,000 active installations. Unauthenticated attackers can upload arbitrary files, including PHP backdoors, to achieve remote code execution. The vendor now reports that attackers are actively exploiting the flaw in the wild.

Wordfence · 13d agoExploit / PoC in the wild

StopAndProtect Turns 2,000 Hacked WordPress Sites Into a Criminal Network

Check Point uncovered StopAndProtect, a cybercrime operation using ~2,000 hacked WordPress sites for ClickFix-driven malware delivery, data theft, surveillance, and ransomware.

Check Point Research identified the StopAndProtect operation in May 2026; it abuses close to 2,000 compromised WordPress sites, many running outdated software, to host malware stages, act as C2, and store stolen data. Infection starts with fake CAPTCHA ClickFix prompts that trick visitors into running a PowerShell command, followed by .NET downloaders deploying ransomware, SMB/USB worm, lockscreen, chat, and credential-stealing components. Rather than always encrypting, operators selectively exfiltrate file lists and specific files; researchers found 700+ stolen-data archives, roughly 31,000 screenshots, and 6,000+ unique victim IP addresses, including WhatsApp activity monitoring.

Security Affairs · 27d agoThreat actor in the wild

Hackers Exploit FortiGate SSL-VPN Flaw to Breach Thai ISP and Deploy MeshCentral Backdoor

Threat actors exploited FortiOS SSL-VPN flaw CVE-2024-21762 to breach Thai ISP Triple T Broadband, gaining root-level persistence via MeshCentral agents.

Attackers exploited CVE-2024-21762, an out-of-bounds write enabling unauthenticated RCE in FortiOS SSL-VPN, against Triple T Broadband's FortiGate 60F at mail.3bb.co.th, launching a Node.js reverse shell via a ROP payload. Hunt.io uncovered the operation through an exposed staging directory at 92.63.180[.]133:8888 containing 298 files of exploits, credential-harvesting scripts, session cookies, and a device inventory. Post-compromise, the actors deployed MeshCentral agents (device group TH-3BB, C2 www.ayuthayatech.com) running as root, plus a hidden SUID backdoor at /usr/local/bin/.rc, and also targeted an internal Pentaho/Tomcat server with Ghostcat (CVE-2020-1938). A cleanup script removed logs, shell histories, and web shells while deliberately preserving the MeshCentral agent and SUID backdoor.

GBHackers · 1d agoExploit / PoC in the wild 3 sourcesCVE-2024-21762CVE-2020-1938

Threat Brief: Ongoing Russia and Ukraine Cyber Activity

Ukrainian government sites were defaced via OctoberCMS CVE-2021-32648 while Microsoft-attributed actor DEV-0586 deployed destructive WhisperGate malware.

Unit 42 tracks January 2022 attacks against Ukrainian government websites that were defaced or made inaccessible, which Ukraine attributed to Russia. Attackers exploited CVE-2021-32648, an account takeover flaw in OctoberCMS prior to 1.0.472, by submitting a boolean true as the password reset code to bypass validation. Separately, WhisperGate malware, attributed by Microsoft to DEV-0586, disabled Windows Defender and corrupted files across multiple Ukrainian organizations, using a ransomware-appearing first stage and an HTTPS-beaconing second stage with LOLBINs and anti-analysis techniques.

Palo Alto Unit 42 · Aug 17, 2026Threat actor in the wildCVE-2021-326481

Brevo supply chain attack hits 100k+ sites with Wordpress backdoors and Clickfix malware

Attackers with Brevo DNS access injected malicious scripts serving ClickFix malware and WordPress backdoors to over 100,000 customer sites on 14 September 2026.

Brevo (formerly Sendinblue), an email marketing platform whose clients include eBay, Louis Vuitton, Michelin and Amnesty International, served injected JavaScript from sendibt1.com domains between 16:05 and 20:12 UTC on 14 September 2026, reaching over 100,000 customer sites and mailing lists. The f.js malware secretly installed a WordPress backdoor plugin from cdn10.sendibt1.com/p/wm.zip using logged-in admins' sessions and showed ClickFix overlays urging visitors to copy-paste and run commands. An SSL certificate for cdn.sendibt1.com created August 25 and attacker-created cdn* DNS records indicate write access to Brevo's Cloudflare DNS, likely via a single Cloudflare account compromise. Sansec recorded 2,549 CSP violation reports across 12 monitored sites; all malicious hosts stopped resolving on 15 September and Brevo's status page lists no incident.

Sansec (Magento / e-commerce security) · 20h agoMalware in the wild

Malcious Admin Menu Editor Pro plugin backdoors 1,500 WordPress sites

Compromised Admin Menu Editor Pro update server distributed backdoored plugin versions installing web shells and hidden admin accounts on roughly 1,500 WordPress sites.

A threat actor with root-level access to adminmenueditor.com pushed trojanized Admin Menu Editor Pro versions 2.35 and 2.36 containing includes/wp-user-consent.php, which installed a web shell and created a hidden wp_-prefixed user account. At least 230 customers and roughly 1,500 sites installed the malicious update, with several hundred more downloads possibly affected. Developer Janis Elsts took the site offline after the attacker recompromised the clean 2.36 release; version 2.34 and the free plugin are believed unaffected.

BleepingComputer · 23h agoMalware in the wild1

U.S. CISA adds Microsoft Windows, N-able N-central, and Adobe flaws to its Known Exploited Vulnerabilities catalog

CISA added four actively exploited flaws to its KEV catalog: Magento StyleSmuggler RCE, two Windows privilege-escalation bugs, and N-able N-central RCE.

CISA added CVE-2026-75650 (Adobe Commerce/Magento, CVSS 10.0), CVE-2026-81963 and CVE-2026-85880 (Microsoft Windows local privilege escalation, CVSS 7.8 each), and CVE-2026-86218 (N-able N-central pre-auth RCE, CVSS 10.0) to its Known Exploited Vulnerabilities catalog. Sansec researchers report the StyleSmuggler Magento flaw, actively exploited since September 4, lets unauthenticated attackers run code on vulnerable online stores and deploy web shells and backdoors; Microsoft confirmed active exploitation of both Windows flaws, and N-able shipped an emergency hotfix. Federal civilian agencies must patch the Windows flaws by September 22, 2026, and the remaining entries by September 11, 2026 under BOD 22-01.

Security Affairsupdated · 2h agofirst · 6d agoExploit / PoC in the wild 19 sourcesCVE-2026-75650CVE-2026-81963CVE-2026-85880+1 CVEs1

August 2026 CVE Landscape

Insikt Group catalogs 73 high-impact August 2026 CVEs (43 Very Critical), including PaperCut, Zimbra, and Metabase flaws actively exploited or weaponized.

Recorded Future's Insikt Group identified 73 high-impact vulnerabilities in August 2026, 43 rated Very Critical, spanning 45 vendors with Microsoft accounting for roughly 11%. 31 vulnerabilities surfaced via CISA's KEV catalog, with others validated via open sources, vendor telemetry, and honeypot data. New Nuclei detection templates were released for CVE-2025-62593 (Ray), CVE-2026-72898 (Metabase), and CVE-2026-9198 (IBM Langflow). The report also highlights two AI-assisted operations: UAT-10147 exploited Zimbra, AjaxPro, Nacos, and Telerik servers before using DeepAudit and PentestGPT post-compromise, while a separate Chinese-speaking actor weaponized Hermes Agent and DeepSeek in a failed attempt.

Recorded Future · 8d agoVulnerability in the wildCVE-2025-62593CVE-2026-72898CVE-2026-9198+4 CVEs1

Magento StyleSmuggler zero-day exploited to deploy Linux backdoor

StyleSmuggler zero-day in Magento and Adobe Commerce is actively exploited in the wild to deploy a Rust-based Linux backdoor; fix not yet released.

A zero-day dubbed StyleSmuggler affecting all versions of Magento and Adobe Commerce is being actively exploited, with the first observed incident on September 4 on a fully patched site. The exploit injects PHP code via Magento's template system through a fake 'failed-payment' email to achieve code execution, installing a Rust-based backdoor disguised as kworker/u:8:0 or fc-cache with a 30-minute cron job for persistence. The backdoor communicates via TLS/WebSockets or UDP port 123 masquerading as NTP traffic, checks TracerPid to detect tracing, and can receive remote commands. Adobe confirmed it is working on a fix with no timeline; Sansec recommends disabling GraphQL as mitigation and monitoring for suspicious cron entries and kworker or fc-cache processes. Magento is installed on more than 160,000 websites, including 14,000 of the top 1 million sites.

BleepingComputer · 9d agoExploit / PoC in the wild

⚡ Weekly Recap: AI-Powered PLC Attacks, GitLab Attacks, Stripe Key Leaks and More

US agencies warn of AI-assisted attacks on exposed Siemens PLCs; the week also saw GitLab CVE-2026-19478 exploited and trojanized npm packages found.

The weekly recap leads with a US government warning that threat actors use AI-generated scripts and Censys/ZoomEye scanning to attack internet-exposed Siemens S7 PLCs in water, energy and manufacturing, calling it an active threat. Other stories include active exploitation of GitLab CVE-2026-19478 (CVSS 9.4, unauthenticated project rewriting), 14 trojanized npm packages delivering the RedC2 4.0 Linux backdoor, and the Zombie Card attack that revives expired Visa cards for contactless payment fraud. It also covers suspected Russian clusters UNC6293, UNC7005 and UNC5976 phishing campaigns, a faster Cloudflare Workers Spectre JWT leak, and a bespoke Cl0p JSP web shell deployed after exploiting PTC Windchill flaws.

The Hacker News · 19d agoThreat actor in the wildCVE-2026-194781

Attackers Target miniOrange SAML Flaws That Can Grant WordPress Admin Access

Attackers are exploiting two unauthenticated WordPress auth bypasses (CVE-2026-61979, CVE-2026-15981, max CVSS 9.8) in miniOrange SAML SSO to gain admin sessions.

Patchstack disclosed two flaws in the Xecurify miniOrange SAML 2.0 Single Sign On WordPress plugin: CVE-2026-15981 (CVSS 9.8) accepts malformed signatures because mo_saml_validate_signature() loosely checks the tri-state result of openssl_verify(), and CVE-2026-61979 (CVSS 8.1) enables privilege escalation via signature algorithm confusion. Both let unauthenticated attackers sign in as any WordPress user, including administrators; fixes shipped in Standard edition versions 17.0.6 and 17.0.5. DigitalOcean observed an attacker using the bypass to obtain an admin session cookie, opportunistic scanning is underway from six IP addresses, and PoC chaining code is public.

The Hacker News · 22d agoExploit / PoC in the wildCVE-2026-61979CVE-2026-15981