https://github.com/ImageMagick/ImageMagick/issues/6775

coders/xbm.c

@@ -177,37 +177,37 @@ static Image *ReadXBMImage(const ImageInfo *image_info,ExceptionInfo *exception)
   Image
     *image;
 
+  IndexPacket
+    *indexes;
+
   int
     c;
 
+
+  long
+    height,
+    width;
+
   MagickBooleanType
     status;
 
-  IndexPacket
-    *indexes;
-
-  ssize_t
-    i,
-    x;
+  MagickOffsetType
+    offset;
 
   PixelPacket
     *q;
 
-  unsigned char
-    *p;
-
-  long
-    height,
-    width;
-
   short int
     hex_digits[256];
 
   ssize_t
+    i,
+    x,
     y;
 
   unsigned char
-    *data;
+    *data,
+    *p;
 
   unsigned int
     bit,
@@ -261,6 +261,7 @@ static Image *ReadXBMImage(const ImageInfo *image_info,ExceptionInfo *exception)
     Scan until hex digits.
   */
   version=11;
+  offset=TellBlob(image);
   while (ReadBlobString(image,buffer) != (char *) NULL)
   {
     if (sscanf(buffer,"static short %1024s = {",name) == 1)
@@ -280,7 +281,10 @@ static Image *ReadXBMImage(const ImageInfo *image_info,ExceptionInfo *exception)
       p++;
     if (LocaleCompare("bits[]",(char *) p) == 0)
       break;
+    offset=TellBlob(image);
   }
+  if (strchr(buffer,'{') != (char *) NULL)
+    (void) SeekBlob(image,offset+(strchr(buffer,'{')-buffer)+1,SEEK_SET);
   /*
     Initialize image structure.
   */
@@ -449,6 +453,7 @@ ModuleExport size_t RegisterXBMImage(void)
   entry->decoder=(DecodeImageHandler *) ReadXBMImage;
   entry->encoder=(EncodeImageHandler *) WriteXBMImage;
   entry->magick=(IsImageFormatHandler *) IsXBM;
+  entry->seekable_stream=MagickTrue;
   entry->adjoin=MagickFalse;
   entry->description=ConstantString(
     "X Windows system bitmap (black and white)");