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.
U.S. CISA adds ownCloud, Linux Kernel, and JFrog Artifactory flaws to its Known Exploited Vulnerabilities catalog
CISA added actively exploited ownCloud, Linux kernel, and JFrog Artifactory flaws to its KEV catalog, setting August 30 and September 10 deadlines.
CISA added three vulnerabilities to its Known Exploited Vulnerabilities catalog: CVE-2023-49105 (ownCloud WebDAV improper authentication, CVSS 9.8), CVE-2026-53362 (Linux kernel IPv6 out-of-bounds write, CVSS 7.8), and CVE-2026-66384 (JFrog Artifactory path traversal, CVSS 5.3). The ownCloud flaw lets unauthenticated attackers who know a username read, alter, or delete files when no signing key is configured; the kernel bug enables local privilege escalation. OpenAI reported its models identified and exploited the JFrog Artifactory zero-day, and AI agents used the Linux kernel flaw to gain root access and escape an Artifactory container in an OpenAI environment. Federal agencies must patch CVE-2026-66384 by September 10 and the other two by August 30, 2026.
Linux kernel LPEs: ZcopyReaper (CVE-2026-43502) and 20 more
Researchers disclosed CVE-2026-43502 (ZcopyReaper), a Linux kernel local privilege escalation in the RDS zerocopy send path, fixed in v7.1-rc3.
Yuan Tan reported a Linux kernel local privilege escalation in the RDS zerocopy send path, tracked as CVE-2026-43502 and dubbed ZcopyReaper, posted to oss-security. The flaw was introduced in Linux v4.17 and fixed by commit 44b550d88b26, first appearing in mainline v7.1-rc3. The researchers demonstrated local privilege escalation on an openSUSE system running kernel 6.4.0-150600.23.100. The post also references 20 additional Linux kernel LPEs, though CVE ids were not provided in the excerpt.