https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=6533

diff --git a/MagickCore/xml-tree.c b/MagickCore/xml-tree.c
index 0cfb025394c06b951fab3f005ed537c9fca84790..008ff5f3ad6aaba27131406cf0ae1936c8d1c509 100644 (file)
--- a/MagickCore/xml-tree.c
+++ b/MagickCore/xml-tree.c
@@ -1726,6 +1726,8 @@ static MagickBooleanType ParseInternalDoctype(XMLTreeRoot *root,char *xml,
         xml+=strspn(xml+8,XMLWhitespace)+8;
         c=xml;
         n=xml+strspn(xml,XMLWhitespace "%");
+        if ((isalpha((int) ((unsigned char) *n)) == 0) && (*n != '_'))
+          break;
         xml=n+strcspn(n,XMLWhitespace);
         *xml=';';
         v=xml+strspn(xml+1,XMLWhitespace)+1;