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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 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.
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Attackers Exploit WooCommerce Wholesale Lead Capture Flaw to Plant PHP Web Shells
Attackers exploit CVE-2026-27540 in WooCommerce Wholesale Lead Capture to upload PHP web shells; Wordfence blocked 100,000+ attempts since June 2026.
Wordfence reports active exploitation of CVE-2026-27540 (CVSS 9.8), an unauthenticated arbitrary file upload in the wwlc_file_upload_handler AJAX action of the WooCommerce Wholesale Lead Capture plugin (versions through 2.0.3.1, 6,000+ installs), enabling remote code execution via uploaded PHP web shells. Over 100,000 exploit attempts were blocked since June 2026, including 99 in the last 24 hours, traced to ten listed IP addresses. Separately, two critical flaws (CVE-2026-78159 and CVE-2026-78006) in The Events Calendar, installed on 600,000+ sites, allow unauthenticated RCE and full site takeover via PHP object injection chains. StellarWP patched the affected plugin versions 6.17.3 and 6.17.4 in releases 6.17.3.1 and 6.17.4.1.
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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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PHP Webshell Campaign Targets WordPress Through Critical WooCommerce Plugin Bug
Wordfence blocked over 100,000 exploitation attempts against CVE-2026-27540 in WooCommerce Wholesale Lead Capture, letting attackers upload PHP webshells to WordPress sites.
Wordfence reported more than 100,000 blocked exploitation attempts against CVE-2026-27540 in the WooCommerce Wholesale Lead Capture plugin (roughly 6,000 active installs), which was disclosed and patched on February 20 in version 2.0.3.2. The unauthenticated AJAX handler wwlc_file_upload_handler reads permitted file extensions from the attacker-controlled request, enabling arbitrary file upload of PHP files such as shell.php that report host details and serve further upload forms. Attack activity peaked between June 4 and June 17, 2026, with additional waves on July 1 and August 30. Wordfence rates the flaw CVSS 9.8, while Patchstack's CVE record lists 9.0.
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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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Critical GiveWP Flaw Lets Attackers Run Commands on WordPress Servers
Critical unauthenticated PHP object injection (CVE-2026-82222) in the GiveWP WordPress donation plugin chains to remote code execution; version 4.16.7.2 fixes it.
Patchstack disclosed CVE-2026-82222 (CVSS 10.0), an unauthenticated PHP object injection in GiveWP versions through 4.16.7.1 that chains through TCPDF and Give\TestData gadget classes to arbitrary OS command execution as the web server user. On versions 4.16.5.1 and below, a default installation with one published donation form is enough to exploit, with no user interaction required. Version 4.16.7.2 blocks unsafe serialized data, hardens the gadget chain and cleans already-stored database records; a separate registration bypass issue remains unresolved.
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Elementor Pro Flaw Could Let Unauthenticated Attackers Upload PHP and Execute Code
Patchstack disclosed CVE-2026-32475 (CVSS 9.0), an unauthenticated file-upload flaw in Elementor Pro enabling PHP upload and RCE; fixed in version 4.2.2.
Patchstack researcher Tin Pham reported an unrestricted file upload flaw in Elementor Pro's Forms module (CVE-2026-32475, CVSS 9.0), affecting all versions up to and including 4.2.1. Submitting two file parts for one field bypasses the extension blocklist and writes attacker-controlled PHP into a public uploads directory, yielding unauthenticated remote code execution when a published Elementor page uses a Form widget with a File Upload field. A patched version 4.2.2 shipped August 19, 2026, a day after WordPress 7.0.4 fixed CVE-2026-65640 (CVSS 8.8), an RCE via Postscript file upload when Imagick and Ghostscript are in use.
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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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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.
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Hackers target WordPress sites via third-party WooCommerce plugin
Attackers exploit unauthenticated file-upload flaw CVE-2026-27540 in WooCommerce Wholesale Lead Capture plugin to install PHP webshells; Wordfence blocked 100,000+ attacks.
CVE-2026-27540 is an unauthenticated arbitrary file-upload vulnerability in the WooCommerce Wholesale Lead Capture premium plugin (versions 2.0.3.1 and older), caused by the exposed wwlc_file_upload_handler AJAX action trusting a user-controlled file_settings allowlist. Discovered by researcher Teemu Saarentaus, it was fixed in version 2.0.3.2 released February 20. Defiant reports Wordfence blocked over 100,000 attacks, with exploitation spikes between June 4-17, July 1, and August 30, delivering shell.php webshells for reconnaissance and additional payload uploads.
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Forminator WordPress Flaw Can Enable Unauthenticated RCE via Malicious PHP Uploads
Wordfence disclosed CVE-2026-15748, a critical unauthenticated file upload flaw enabling RCE in the Forminator Forms WordPress plugin, patched in version 1.56.2.
Wordfence reported CVE-2026-15748 (CVSS 9.8) in Forminator Forms, a WordPress plugin with over 600,000 active installations, allowing unauthenticated attackers to upload arbitrary PHP files and achieve remote code execution. The flaw stems from insufficient file type validation in the handle_file_upload() function, and exploitation requires a form containing both a File Upload field and a Select field, plus a custom upload storage root lacking .htaccess PHP protection. All versions up to and including 1.56.1 are affected; version 1.56.2 released July 31, 2026 fixes the issue. Wordfence also disclosed CVE-2026-15826 (CVSS 9.8), an authentication bypass in User Profile Builder (40,000+ installs) letting unauthenticated attackers log in as administrator, fixed in version 3.16.5 on July 16, 2026.
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