CFITSIO through 4.7.0 contains a heap-based out-of-bounds read vulnerability in the HCOMPRESS tile decoder that allows attackers to read past the compressed tile buffer via inputnnybble in fitshdecompress.c. Attackers can supply a crafted FITS file with ZCMPTYPE HCOMPRESS1 declaring oversized tile geometry to crash applications calling fitsreadpix or disclose limited heap memory.