As changelog says:

v3.31.0

(...) Benehalo has uncovered a number of security problems in the liblouis code and has thankfully also provided fixes for them by hardening the code. (...)
...

• Benehalo discovered quite a number of security problems and kindly enough also just fixed them by adding some check guards and making the code more robust.

v3.30.0

• Fix a memory problem when handling parameters in lou_translate, thanks to benehalo.

v3.28.0

• Fix a memory corruption error in the code for the swap opcodes. Thanks to the OSS-fuzz project for reporting and to Christian Egli for fixing it.