ACCORDING to CISA, the GPL Odorizers GPL750 advisory notes a vulnerability that could let a low privileged remote attacker manipulate register values, causing too much or too little odorant to be injected into a gas line. The vulnerability affects GPL Odorizers GPL750 in several configurations: GPL750 (XL4) >= v1.0|<v6.0, GPL750 (XL4 Prime) >= v4.0|<v6.0, GPL750 (XL7) >= v13.0|<v20.0, and GPL750 (XL7 Prime) >= v18.4|<v20.0, with CVSS v3.1 base score 8.6 (HIGH).
The associated CVE is CVE-2026-4436, which describes how a low-privileged remote attacker could send Modbus packets to manipulate inputs to the odorant injection logic. Mitigations include updating to the latest GPL750 software version in conjunction with the latest Horner Automation firmware for the XL4, XL4 Prime, XL7 and XL7 Prime devices, and following steps to prepare microSD cards by removing outdated files while retaining the LOGS folder and FIRMWARE[.]LIC. For assistance, contact GPL Odorizers at (303) 697-6701, and Horner Automation’s firmware guidance is available on their site.