file: /proc/sys/net/ipv4/conf/interface/secure_redirects
variable: net.ipv4.conf.interface.secure_redirects
Official reference

Accept ICMP redirect messages only to gateways listed in the interface’s current gateway list. Even if disabled, RFC1122 redirect rules still apply. Overridden by shared_media. secure_redirects for the interface will be enabled if at least one of conf/{all,interface}/secure_redirects is set to TRUE, it will be disabled otherwise default TRUE

Nb: per interface setting (where “interface” is the name of your network interface); “all” is a special interface: changes the settings for all interfaces.