This is Debian bug https://bugs.debian.org/868151 reported by Jakub Wilk. A test case is attached to the Debian bug report.
loader_xpm.c contains the following code:
sscanf(line, "%i %i %i %i", &w, &h, &ncolors, &cpp); if ((ncolors > 32766) || (ncolors < 1)) ...
This doesn't check return value from sscanf(), so for some invalid XMP files
(such as the attached one), the ncolors variable will remain uninitialized.
Found using american fuzzy lop: