Transformation **parityOdd7bit** needs to be implemented inside libmodsecurity. The documentation of the transformation can be found here: https://github.com/SpiderLabs/ModSecurity/wiki/Reference-Manual#parityOdd7bit The file already exist in the repository: https://github.com/SpiderLabs/ModSecurity/blob/libmodsecurity/src/actions/transformations/parity_odd_7bit.cc