This indicates an attack attempt to exploit a Directory Traversal vulnerability in TP-Link TL-R600VPN HTTP Server.
The vulnerability is due to an error in the vulnerable application when handling a maliciously crafted request. A remote attacker may be able to exploit this to read arbitrary files on the system.
TP-Link TL-R600VPN HWv2 FRNv1.2.3
TP-Link TL-R600VPN HWv3 FRNv1.3.0
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.