In the PatternMatch function in fontfile/fontdir.c in libXfont through 1.5.2 and 2.x before 2.0.2, an attacker with access to an X connection can cause a buffer over-read during pattern matching of fonts, leading to information disclosure or a crash (denial of service). This occurs because '\0' characters are incorrectly skipped in situations involving ? characters.
https://www.x.org/releases/individual/lib/libXfont2-2.0.2.tar.bz2
https://security.gentoo.org/glsa/201711-08
https://cgit.freedesktop.org/xorg/lib/libXfont/commit/?id=d1e670a4a8704b8708e493ab6155589bcd570608
https://bugzilla.suse.com/show_bug.cgi?id=1054285