MagickExport ssize_t ReadBlob(Image *image,const size_t length,
  unsigned char *data)
{
  BlobInfo
    *magick_restrict blob_info;

  int
    c;

  register unsigned char
    *q;

  ssize_t
    count;

  assert(image != (Image *) NULL);
  assert(image->signature == MagickCoreSignature);
  assert(image->blob != (BlobInfo *) NULL);
  assert(image->blob->type != UndefinedStream);
  if (length == 0)
    return(0);
  assert(data != (void *) NULL);
  blob_info=image->blob;
  count=0;
  q=data;
  switch (blob_info->type)
  {
    case UndefinedStream:
      break;
    case StandardStream:
    case FileStream:
    case PipeStream:
    {
      switch (length)
      {
        default:
        {
          count=(ssize_t) fread(q,1,length,blob_info->file_info.file);
          break;
        }
        case 4:
        {
          c=getc(blob_info->file_info.file);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 3:
        {
          c=getc(blob_info->file_info.file);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 2:
        {
          c=getc(blob_info->file_info.file);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 1:
        {
          c=getc(blob_info->file_info.file);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 0:
          break;
      }
      break;
    }
    case ZipStream:
    {
#if defined(MAGICKCORE_ZLIB_DELEGATE)
      switch (length)
      {
        default:
        {
          register ssize_t
            i;

          for (i=0; i < (ssize_t) length; i+=count)
          {
            count=(ssize_t) gzread(blob_info->file_info.gzfile,q+i,
              (unsigned int) MagickMin(length-i,MagickMaxBufferExtent));
            if (count <= 0)
              {
                count=0;
                if (errno != EINTR)
                  break;
              }
          }
          count=i;
          break;
        }
        case 4:
        {
          c=gzgetc(blob_info->file_info.gzfile);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 3:
        {
          c=gzgetc(blob_info->file_info.gzfile);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 2:
        {
          c=gzgetc(blob_info->file_info.gzfile);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 1:
        {
          c=gzgetc(blob_info->file_info.gzfile);
          if (c == EOF)
            break;
          *q++=(unsigned char) c;
          count++;
        }
        case 0:
          break;
      }
#endif
      break;
    }
    case BZipStream:
    {
#if defined(MAGICKCORE_BZLIB_DELEGATE)
     register ssize_t
        i;

      for (i=0; i < (ssize_t) length; i+=count)
      {
        count=(ssize_t) BZ2_bzread(blob_info->file_info.bzfile,q+i,
          (unsigned int) MagickMin(length-i,MagickMaxBufferExtent));
        if (count <= 0)
          {
            count=0;
            if (errno != EINTR)
              break;
          }
      }
      count=i;
#endif
      break;
    }
    case FifoStream:
      break;
    case BlobStream:
    {
      register const unsigned char
        *p;

      if (blob_info->offset >= (MagickOffsetType) blob_info->length)
        {
          blob_info->eof=MagickTrue;
          break;
        }
      p=blob_info->data+blob_info->offset;
      count=(ssize_t) MagickMin((MagickOffsetType) length,(MagickOffsetType)
        blob_info->length-blob_info->offset);
      blob_info->offset+=count;
      if (count != (ssize_t) length)
        blob_info->eof=MagickTrue;
      (void) memcpy(q,p,(size_t) count);
      break;
    }
  }
  return(count);
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.