The RESOLV::lookup iRule command in F5 BIG-IP LTM, APM, ASM, and Link Controller 10.2.1 through 10.2.4, 11.2.1, 11.4.x, 11.5.x before 11.5.4 HF2, 11.6.x before 11.6.1, and 12.0.0 before HF3; BIG-IP AAM, AFM, and PEM 11.4.x, 11.5.x before 11.5.4 HF2, 11.6.x before 11.6.1, and 12.0.0 before HF3; BIG-IP Analytics 11.2.1, 11.4.x, 11.5.x before 11.5.4 HF2, 11.6.x before 11.6.1, and 12.0.0 before HF3; BIG-IP DNS 12.0.0 before HF3; BIG-IP Edge Gateway, WebAccelerator, and WOM 10.2.1 through 10.2.4 and 11.2.1; BIG-IP GTM 10.2.1 through 10.2.4, 11.2.1, 11.4.x, 11.5.x before 11.5.4 HF2, and 11.6.x before 11.6.1; and BIG-IP PSM 10.2.1 through 10.2.4 and 11.4.0 through 11.4.1 allows remote DNS servers to cause a denial of service (CPU consumption or Traffic Management Microkernel crash) via a crafted PTR response.