In libImaging/PcxDecode.c in Pillow before 7.1.0, an out-of-bounds read can occur when reading PCX files where state->shuffle is instructed to read beyond state->buffer.
https://usn.ubuntu.com/4430-2/
https://usn.ubuntu.com/4430-1/
https://pillow.readthedocs.io/en/stable/releasenotes/7.1.0.html