Citrix confirmed that two critical NetScaler remote code execution vulnerabilities, CVE-2026-88771 and CVE-2026-88772, are being exploited in attacks, and released fixes. These are the same zero-days that researchers, IT providers, and national cyber agencies warned about privately over the weekend, with some advising immediate NetScaler shutdowns. Organizations commonly deploy NetScaler as internet-facing edge devices for remote access and application delivery, so compromising one gives attackers a foothold at the network perimeter and a potential path to internal systems without first landing on an internal endpoint. CISA added the flaws to its Known Exploited Vulnerabilities catalog with a near-term federal patch deadline.
Researchers at Sophos and ESET found attackers breaching F5 BIG-IP APM access gateways and installing a stealthy Linux rootkit that ESET calls PoisonedRefresh. Rather than dropping a file on disk, it hides a web shell in memory, hooks into the Apache and PHP components, tampers with SELinux settings, and uses disguised requests to run commands while blending into normal traffic. Crucially, it persists across device upgrades, so patching the appliance alone does not remove it. The intrusions likely began by exploiting a critical remote code execution flaw that F5 had earlier downgraded to a mere denial-of-service issue, which may have led some organizations to deprioritize patching it.
Citrix patched a critical flaw in NetScaler ADC and Gateway that lets a remote, unauthenticated attacker bypass authentication on appliances used for remote access. Tracked as CVE-2026-19490 and scored 9.3, it is an authentication-bypass issue affecting devices configured as a gateway for SSL VPN, ICA proxy, clientless VPN, or RDP proxy, or as an AAA authentication server. On newer builds it requires a SAML configuration, but on older builds any gateway or AAA configuration is exposed. There is no confirmed exploitation yet, but NetScaler appliances sit at the network edge and have repeatedly been attacked soon after disclosure, so patching is urgent.
A critical flaw in Progress Kemp LoadMaster lets an unauthenticated attacker run commands as root on the appliance by sending a crafted request to its API. Rated 9.8, the bug (CVE-2026-8037) sits in a function meant to sanitize input before it reaches a shell command, and LoadMaster's position as an edge load balancer and application delivery controller makes a pre-authentication flaw especially dangerous, since it can turn a protective choke point into a direct foothold. Progress patched it in early June, and researchers at watchTowr published a full technical write-up with a working proof-of-concept on June 29. No exploitation has been reported yet, but Progress also makes MOVEit, a past mass-exploitation target.
TrustStrike Labs