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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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Exposed Vite servers are being probed for AWS and Azure credentials
F5 honeypots logged 32,000+ probes against Vite file-access bypass CVE-2026-39364, hunting AWS and Azure credentials on exposed dev servers.
F5 Labs reported 32,000+ scan attempts (807 attack sessions) against exposed Vite servers in August, up from 1,732 attempts over the prior three months. Attackers exploited CVE-2026-39364 (CVSS 8.2), which bypasses Vite's server.fs.deny protection via parameters like ?raw and ?import&raw, affecting Vite 7.1.0 to before 7.3.2 and Vite 8 before 8.0.5. Scanners cycled wordlists for environment files, AWS keys, Azure tokens and IaC state files, also combining older Vite CVEs (2025-30208, 2025-31125, 2024-45811) and probing a Next.js middleware bypass. Only CVE-2025-31125 is currently in CISA's KEV catalog.
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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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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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New infosec products of the month: August 2026
August 2026 roundup of security product releases from ServiceNow, Tanium, Snyk, F5, A10, Searchlight Cyber, Intezer, NETSCOUT, Tufin, and Abnormal AI.
Help Net Security's monthly product roundup covers roughly a dozen vendors. Highlights include Snyk's general availability of Evo Continuous Offensive Security with AI-powered pentesting and AI agent red teaming, Searchlight Cyber's PTEM platform combining exposure visibility with attacker intelligence, and A10 and F5 AI gateways to govern enterprise LLM and agent usage. Other updates include Abnormal AI email DLP and phishing training, NETSCOUT outbound DDoS mitigation for service providers, Intezer's native Workflows automation, and Tufin's AI-powered Segmentation Intelligence.
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New infosec products of the week: August 21, 2026
Weekly product roundup covering NETSCOUT outbound DDoS mitigation, F5 AI Gateway enhancements, Intezer Workflows, and Tufin TOS 5.3.
NETSCOUT extended Adaptive DDoS Protection to automatically mitigate outbound attack traffic for service providers. F5 enhanced its AI Gateway and integrated it into the F5 AI Security Platform for unified AI access governance. Intezer launched Workflows, native automation and response inside its platform without a separate SOAR, and Tufin released Orchestration Suite 5.3 with AI-powered Segmentation Intelligence for multi-vendor environments.
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F5 Warns of a New Critical BIG
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F5 Releases Critical Security Patch for BIG-IP and BIG
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