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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.

BleepingComputer · 7d agoMalware in the wildCVE-2025-53521

F5 enhances AI Gateway to control AI costs, access, and security

F5 integrated AI Gateway into its AI Security Platform, adding model routing, MCP governance, and guardrails, claiming up to 60% token spend reduction.

F5 announced AI Gateway enhancements combining a Model Gateway for cost optimization, an MCP Gateway for agent-to-tool access control, and AI Guardrails for prompt and response inspection. The company cited its 2026 State of Application Strategy Report finding 77% of organizations now treat inference as their dominant AI activity and manage an average of seven AI models. F5 claims smart routing, semantic caching, and GPU-aware load balancing can cut token spend by up to 60% without application changes. The gateway enforces budgets, model routing policies, and agent access controls centrally across SaaS, hybrid SaaS, and hybrid multicloud deployments, with air-gapped support planned.

Help Net Security · 28d agoAI tools & infra

Related CVEs

  • CVE-2025-535219.32%
    Stack-Based Buffer Overflow in F5 BIG-IP APM Enables Unauthenticated RCE
    CVE-2025-53521 is a stack-based buffer overflow (CWE-121) in F5 BIG-IP's Access Policy Manager (APM) that allows remote code execution. The flaw is triggered when a virtual server is configured with an APM access policy and receives specific malicious network traffic; no authentication or user interaction is required per the CVSS 4.0 vector. An attacker who exploits it gains remote code execution on the BIG-IP device, and in observed intrusions attackers have deployed a fileless Linux rootkit (dubbed 'PoisonedRefresh') that injects a PHP web shell into server memory to evade disk-based scanning. Any F5 BIG-IP deployment with an APM access policy configured on a virtual server is potentially affected; versions that have reached End of Technical Support are not evaluated by the vendor. The vulnerability is being actively exploited in the wild — it was added to CISA's Known Exploited Vulnerabilities catalog on 2026-03-27, with active exploitation and in-memory malware campaigns confirmed in press reports, though ransomware use is unknown.
    · F5 BIG-IP (BIG-IP Access Policy Manager / APM) KEVlarge

Appears with

vendor F5 2organization ESET 1organization Gartner 1organization Help Net Security 1organization ShadowServer Foundation 1organization Sophos 1product Apache 1product F5 AI Gateway 1product F5 AI Security Platform 1product F5 BIG-IP APM 1vendor ESET 1vendor ShadowServer Foundation 1malware PoisonedRefresh 1vendor Sophos 1
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