The AppFirewall functionality in Citrix NetScaler Application Delivery Controller and NetScaler Gateway 10.5 before Build 68.7, 11.0 before Build 71.24, 11.1 before Build 58.13, and 12.0 before Build 57.24 allows remote attackers to execute arbitrary code via unspecified vectors.
A statement in the System Programming Guide of the Intel 64 and IA-32 Architectures Software Developer's Manual (SDM) was mishandled in the development of some or all operating-system kernels, resulting in unexpected behavior for #DB exceptions that are deferred by MOV SS or POP SS, as demonstrated by (for example) privilege escalation in Windows, macOS, some Xen configurations, or FreeBSD, or a Linux kernel crash. The MOV to SS and POP SS instructions inhibit interrupts (including NMIs), data breakpoints, and single step trap exceptions until the instruction boundary following the next instruction (SDM Vol. 3A; section 6.8.3). (The inhibited data breakpoints are those on memory accessed by the MOV to SS or POP to SS instruction itself.) Note that debug exceptions are not inhibited by the interrupt enable (EFLAGS.IF) system flag (SDM Vol. 3A; section 2.3). If the instruction following the MOV to SS or POP to SS instruction is an instruction like SYSCALL, SYSENTER, INT 3, etc. that transfers control to the operating system at CPL < 3, the debug exception is delivered after the transfer to CPL < 3 is complete. OS kernels may not expect this order of events and may therefore experience unexpected behavior when it occurs.
NetScaler ADC 10.5, 11.0, 11.1, and 12.0, and NetScaler Gateway 10.5, 11.0, 11.1, and 12.0 allow remote attackers to download arbitrary files on the target system.