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.
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.
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.
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.
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.
Canada's Cyber Centre relayed an F5 advisory (AV26-878) covering vulnerabilities in BIG-IP, BIG-IQ, NGINX components, and APM clients.
The Canadian Centre for Cyber Security published advisory AV26-878 noting F5 vulnerabilities affecting BIG-IP all modules prior to 17.1.3.4, 17.5.1.8, 21.0.0.3, and 21.1.0.1, plus BIG-IQ prior to 8.4.2.1, NGINX Gateway Fabric, NGINX Ingress Controller, NGINX JavaScript 9.9, and APM clients. F5 issued an out-of-band security notification (K000162872) on September 2, 2026. Administrators are encouraged to review the linked advisory and apply updates as they become available.
FBI and Lumen disrupted QTFY's QScan and QTRouter botnet platforms used by Chinese state-sponsored hackers to conceal intrusions into U.S. agencies.
The U.S. DoJ announced court-authorized seizure of domains behind QScan and QTRouter, operated by the Chinese state-sponsored group QTFY and employed by Nanjing Xinjiuwei Network Technology Company. QTFY has been active since May 2018 and targeted NASA, the Federal Reserve, the Department of Energy, DoJ, HHS, NIH, the U.S. Senate, and academic institutions. QScan exploits vulnerable IoT devices, feeding them into QTRouter, an OpenWrt-based proxy obfuscation network likened to an operational relay box (ORB) that masks attack origins. The group exploited zero-days such as Ivanti CSA flaws CVE-2024-8190, CVE-2024-8963, and CVE-2024-9380, plus numerous N-days, and maintained persistence with RATs, web shells, and legitimate credentials.
F5 added anomaly detection and agentic threat intelligence to its AI-powered WAF, enabling virtual patch enforcement against exploits within minutes.
F5 announced enhancements to F5 WAF for Distributed Cloud, adding anomaly detection that builds per-application traffic baselines and agentic threat intelligence built on technology from the Fletch acquisition. The AI-powered WAF scores each request in real time with a neural network risk engine, and internal testing claims 98% threat detection efficacy with false positives reduced to 1%. Automated virtual patching via Distributed Cloud Web App Scanning extends to F5 WAF for BIG-IP, letting teams block actively exploited vulnerabilities at the request level in minutes; agentic features are rolling out over coming months.
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.
FBI and DOJ seized QTFY infrastructure, disrupting a Chinese state-sponsored group that compromised federal agencies and critical infrastructure since 2018.
Authorities seized three domains powering QScan and QTRouter, the hacking suite of QTFY, a Chinese government-funded group operating through front company Nanjing Xinjiuwei Network Technology. Targets include the Departments of Energy, Justice, and Health and Human Services, the Federal Reserve, NASA, NIH, financial institutions, defense contractors, utilities, telecoms, and hospitals; the group exploited zero-days in Ivanti, Pulse Secure, Fortinet, Citrix, and others, intruding three DOE national labs in September 2024. QScan carried over 200 proof-of-concept exploits and processed more than two million scanning tasks in a single day in 2024.
FBI seizes China-linked QScan and QTRouter hacking platforms used by QTFY to obfuscate intrusions against US federal agencies.
The DOJ and FBI seized domains hard-coded into QScan and QTRouter, two platforms operated by China-based Nanjing Xinjiuwei Network Technology Company on behalf of state-sponsored group QTFY. QScan automatically infected thousands of IoT devices which were added to QTRouter, an obfuscation network routing malicious traffic through compromised and proxy devices outside China. Targets included NASA, the Federal Reserve, Departments of Energy, Justice, and HHS, NIH, and the US Senate, exploiting flaws in Fortinet SSL-VPN, Citrix ADC, Microsoft Exchange, F5 BIG-IP, Log4j, and others.
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.
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.
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.
JNDI Injection Remote Code Execution in Apache Log4j2 (Log4Shell)
Apache Log4j2, an extremely widely used Java logging library, fails to protect its JNDI lookup feature against attacker-controlled JNDI-related endpoints (CWE-20, CWE-502), so crafted text processed by the logger causes the Java runtime to fetch and load attacker-supplied objects, leading to remote code execution. The flaw is triggered whenever attacker-controlled input reaches the logging API and is parsed for JNDI lookups, a pattern common in web servers and enterprise Java applications that log user-supplied fields such as headers or form values. Successful exploitation yields arbitrary code execution under the privileges of the affected application, giving attackers a foothold for lateral movement, data theft, and ransomware deployment. Any Java application or product that ships or bundles an affected Apache Log4j2 release is exposed, making this one of the most broadly deployed vulnerabilities ever disclosed. Exploitation is confirmed in the wild: CISA added it to the Known Exploited Vulnerabilities catalog on 2021-12-10 with known ransomware use, and EPSS assigns a 100% probability of exploitation within 30 days.
Unauthenticated RCE in Kentico Xperience Staging Service
CVE-2019-10068 is a .NET deserialization flaw (CWE-502) in the Kentico Xperience staging service that stems from a failure to validate security headers on incoming requests. Because of this, a specially crafted request can bypass the staging service's initial authentication and reach the deserialization routine with attacker-controlled .NET object data. Successful exploitation yields unauthenticated remote code execution on the server hosting the Kentico instance, with full confidentiality, integrity, and availability impact (CVSS 3.1: 9.8). All Kentico 9.x releases and 10.0.x, 11.0.x, and 12.0.x branches prior to the fixed builds (10.0.52, 11.0.48, 12.0.15) are affected. Exploitation is confirmed: the flaw is in CISA's Known Exploited Vulnerabilities catalog (added 2022-03-25), carries a very high EPSS score of 95.1%, and a public proof-of-concept for Kentico CMS 12.0.14 remote command execution is available.
· Kentico Xperience (Kentico CMS) 9.x (all); 10.0.x before 10.0.52; 11.0.x before 11.0.48; 12.0.x before 12.0.15 KEV PoC large
Authentication Bypass in CrushFTP File Transfer Servers (CVE-2025-31161)
CrushFTP contains an authentication bypass (CWE-305) in its handling of the HTTP authorization header, allowing crafted header values to grant access without valid credentials. A remote, unauthenticated attacker who can reach the server's HTTP/HTTPS interface can use this flaw to authenticate as any known or guessable account, such as the built-in crushadmin user. With administrative access, the attacker can typically achieve full compromise of the file-transfer server, including access to hosted files and user accounts. Any organization running CrushFTP is affected, with internet-exposed instances at the highest risk. The flaw is being actively exploited: it was added to CISA's KEV on 2025-04-07 with known ransomware use, and EPSS assigns it a 100% probability of exploitation within 30 days.
Unauthenticated Path Traversal in Fortinet FortiOS SSL VPN
CVE-2018-13379 is a path traversal flaw (CWE-22) in the Fortinet FortiOS SSL VPN web portal that allows an unauthenticated attacker to download FortiOS system files via specially crafted HTTP resource requests. By traversing directories through crafted requests to the exposed web portal, the attacker can retrieve sensitive files, a technique publicly documented as yielding the SSL VPN session file containing usernames and passwords in plaintext. Any organization running the SSL VPN web portal on a FortiGate appliance is affected, and risk is highest where the portal is directly reachable from the internet. The flaw is confirmed in the wild: it was added to the CISA KEV catalog on 2021-11-03 with known ransomware use, and EPSS assigns it a 100% probability of exploitation within 30 days. No public PoC is listed in the provided data, but credential theft tied to this bug has been widely reused by threat actors.
Unauthenticated RCE via path traversal in F5 BIG-IP TMUI
CVE-2020-5902 is a critical, unauthenticated remote code execution flaw in the F5 BIG-IP Traffic Management User Interface (TMUI), the appliance's web management console, rooted in a directory/path traversal issue (CWE-22) in undisclosed TMUI pages. It is triggered by sending crafted HTTP(S) requests to the management interface — classically path-traversal URLs beneath the TMUI application on the management port — which lets an attacker bypass authentication, read or delete arbitrary files, and execute commands without credentials. Successful exploitation yields full control of the BIG-IP system, which attackers can use to pivot into networks the appliance fronts, maintain persistence, and deploy ransomware. Any organization running an affected F5 BIG-IP appliance or virtual edition whose TMUI is reachable, or whose management network can be reached, is exposed; F5's installed base spans large enterprises and service providers, so the footprint is broad. Exploitation is confirmed in the wild: the flaw was mass-scanned and exploited within days of its July 2020 disclosure, it is listed in CISA KEV with known ransomware use, and EPSS assigns a ~100% probability of exploitation within 30 days.
Unauthenticated SSRF/RCE in Microsoft Exchange Server (ProxyLogon)
CVE-2021-26855 is a server-side request forgery flaw (CWE-918) in Microsoft Exchange Server that allows an unauthenticated remote attacker to send specially crafted HTTP requests and have the Exchange server process them as itself, disclosing sensitive session information. When chained with sibling Exchange flaws (the 'ProxyLogon' chain), it yields authentication bypass and arbitrary file write, escalating to full remote code execution with SYSTEM-level privileges on the on-premises Exchange server. Any organization running an affected on-premises Exchange server reachable over HTTP/HTTPS (typically outbound webmail) is exposed; Exchange Online was not affected. Exploitation is confirmed in the wild at large scale: the flaw was mass-exploited beginning in early 2021 (notably by the HAFNIUM group), is on the CISA KEV with documented ransomware use, and has a maximum EPSS score of 100% (100th percentile), despite no public PoC listing.
· Microsoft Exchange Server On-premises Exchange Server editions supported in the vendor's March 2021 guidance (Exchange Server 2013, 2016, and 2019), prior to the March 2021 security upda KEV ransomware PoC ×4mass
Information Disclosure in Internet-Facing Check Point Quantum Security Gateways
Check Point Quantum Security Gateways contain an information disclosure flaw (CWE-200) that can expose information stored on the appliance to unauthorized parties. It is triggered when an attacker targets a gateway connected to the internet with IPSec VPN, Remote Access VPN, or Mobile Access enabled, sending crafted requests to the exposed VPN services. A successful attacker gains unauthorized access to information on the gateway, and CISA notes known use of this flaw in ransomware campaigns. The issue spans multiple Check Point product lines: CloudGuard Network, Quantum Scalable Chassis, Quantum Security Gateways, and Quantum Spark Appliances. Exploitation is confirmed in the wild: the flaw was added to CISA's KEV catalog on 2024-05-30 with ransomware use listed, and EPSS assigns a 100% probability of exploitation within 30 days, though no public proof-of-concept is known.
· Check Point Quantum Security Gateways · Check Point CloudGuard Network KEV ransomwarelarge
OS Command Injection RCE in Ivanti Cloud Services Appliance 4.6
Ivanti Cloud Services Appliance versions 4.6 Patch 518 and before contain an OS command injection flaw (CWE-78) that allows a remote, authenticated attacker to achieve remote code execution. The attacker must already hold administrator-level privileges on the appliance, and exploitation is triggered by sending crafted input to the appliance over the network. Successful exploitation yields arbitrary command execution on the CSA, and related reporting indicates nation-state actors have been exploiting Ivanti CSA flaws for network infiltration, including attacks on French government and telecom targets. Only organizations still running CSA 4.6.x are affected, and that product line has reached end-of-life and will not receive further security updates. The vulnerability was added to CISA's Known Exploited Vulnerabilities catalog on 2024-09-13 and carries a very high EPSS score (88.5%, 100th percentile), signaling confirmed and likely ongoing exploitation in the wild.
· Ivanti Cloud Services Appliance 4.6 through Patch 518 (versions 4.6 Patch 518 and before) KEVmoderate
OS Command Injection RCE in Ivanti Cloud Services Appliance Admin Console
CVE-2024-9380 is an OS command injection flaw (CWE-77/CWE-78) in the admin web console of Ivanti Cloud Services Appliance (CSA), fixed in version 5.0.2. A remote attacker who is already authenticated with administrative privileges can inject arbitrary operating system commands through the console, which the appliance then executes. Successful exploitation yields remote code execution with high impact on confidentiality, integrity, and availability (CVSS 3.1: 7.2). All CSA releases before 5.0.2 are affected, and the widely deployed 4.6.x line has reached End-of-Life, so EOL users must remove it from service or move to 5.0.x or later. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2024-10-09, and contemporaneous reporting describes Chinese nation-state actors exploiting Ivanti CSA zero-days against French government and telecom targets, with a 63.2% EPSS probability of exploitation in the next 30 days (99th percentile).
· Ivanti Endpoint Manager Cloud Services Appliance (CSA) all versions before 5.0.2, including the End-of-Life 4.6.x line KEVmoderate
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