SAIL is a cross-platform library for loading and saving images with support for animation, metadata, and ICC profiles. Prior to 1.0.0, sail_codec_load_frame_v8_xbm() in src/sail-codecs/xbm/xbm.c allocates the decoded pixel buffer using the X11 one-byte-per-literal layout, but an X10 static short file causes the flat decode loop to write two file-controlled bytes per literal. When ceil(width/8) produces an odd row stride, the X10 literal count includes a padding byte for every row, but the destination has no space for those bytes, so loading the XBM through sail_load_from_file, sail_load_from_memory, or sail_start_loading_* produces a forward heap overwrite that scales with image height. The X11 static char path is not affected. The overwrite can corrupt process state, cause reliable crashes, and potentially enable code execution in a susceptible consuming application. This issue is fixed in version 1.0.0.