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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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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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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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USN-8734-1: PHP vulnerabilities
Ubuntu issued USN-8734-1 fixing three PHP denial-of-service flaws in SOAP, metaphone() and phar handling, including CVE-2026-7262 and CVE-2026-7568.
Ubuntu security notice USN-8734-1 addresses multiple PHP vulnerabilities. CVE-2026-7262 is a NULL pointer dereference in Apache map decoding in SOAP servers with a typemap configured; CVE-2026-7568 is a signed integer overflow in metaphone() causing an out-of-bounds read; and CVE-2026-7260 involves unbounded recursion from circular symbolic links in phar archives. All issues could allow remote attackers to cause denial-of-service conditions.
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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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USN-8743-1: PHP vulnerabilities
Ubuntu fixes three PHP flaws, including SQL injection in the PostgreSQL extension (CVE-2026-17543) and an out-of-bounds write in bccomp().
Ubuntu Security Notice USN-8743-1 patches three vulnerabilities in PHP. CVE-2026-17543 involves incorrect backslash escaping in the PostgreSQL extension enabling SQL injection. CVE-2026-17544 is an out-of-bounds write in bccomp() that could cause denial of service or arbitrary code execution on Ubuntu 26.04 LTS, and CVE-2026-7260 causes unbounded recursion via circular symlinks in phar archives.
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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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Adobe Patches Magento Zero-Day Exploited to Deploy Rust Backdoor and PHP Web Shell
Adobe patches actively exploited Magento zero-day CVE-2026-75650 (CVSS 10.0), abused since Sept 4 to deploy a Rust backdoor and PHP web shells.
Adobe released an emergency hotfix (VULN-39341) for CVE-2026-75650 (CVSS 10.0), dubbed StyleSmuggler by Sansec, which abuses Magento's template system via PHP code injection to trigger unauthenticated remote code execution in Adobe Commerce and Magento Open Source. Exploitation began September 4, 2026, with attackers deploying a Rust-based Linux backdoor and a PHP dropper that writes a web shell; one managed server was compromised 50 minutes after the first report. Previdian honeypots recorded 12 exploitation attempts from two unique IPs in China and Romania since September 7, all unsuccessful. Adobe urges merchants to apply the patch and rotate encryption keys.
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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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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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