Mar 27, 2026 - For details about updated CVE-2025-53521 (BIG-IP APM vulnerability), refer to K000156741.

Forum Discussion

MFS_324204's avatar
MFS_324204
Icon for Nimbostratus rankNimbostratus
Dec 22, 2017

F5 LC http health monitor get blocked by F5 ASM

Is there a known issue when we do health monitor using http from F5 LC to server behind F5 ASM? Attack mentioned per below: `**Unparsable request content HTTP version not found**`
application delivery
ASM Advanced WAF
LTM
security
crodriguez's avatar
crodriguez
Ret. Employee
Dec 22, 2017

Per K10280, ASM's default behavior with respect to HTTP protocol compliance is to flag an HTTP request as bad if it is not using HTTP version 1.0 or higher. By default, the BIG-IP system uses HTTP 0.9 when sending monitor requests. By specifying the HTTP version in the Send String of the monitor, you can force the system to send an HTTP 1.0 or 1.1 request. See K2167 for help with constructing HTTP requests for use with the HTTP or HTTPS health monitor.