An issue was discovered on PHOENIX CONTACT AXL F BK PN <=1.0.4, AXL F BK ETH <= 1.12, and AXL F BK ETH XC <= 1.11 devices and Bosch Rexroth S20-ETH-BK and Rexroth S20-PN-BK+ (the S20-PN-BK+/S20-ETH-BK fieldbus couplers sold by Bosch Rexroth contain technology from Phoenix Contact). Incorrect handling of a request with non-standard symbols allows remote attackers to initiate a complete lock up of the bus coupler. Authentication of the request is not required.