MagickExport unsigned char *FileToBlob(const char *filename,const size_t extent,
  size_t *length,ExceptionInfo *exception)
{
  int
    file;

  MagickBooleanType
    status;

  MagickOffsetType
    offset;

  register size_t
    i;

  ssize_t
    count;

  struct stat
    attributes;

  unsigned char
    *blob;

  void
    *map;

  assert(filename != (const char *) NULL);
  (void) LogMagickEvent(TraceEvent,GetMagickModule(),"%s",filename);
  assert(exception != (ExceptionInfo *) NULL);
  *length=0;
  status=IsRightsAuthorized(PathPolicyDomain,ReadPolicyRights,filename);
  if (status == MagickFalse)
    {
      errno=EPERM;
      (void) ThrowMagickException(exception,GetMagickModule(),PolicyError,
        "NotAuthorized","`%s'",filename);
      return(NULL);
    }
  file=fileno(stdin);
  if (LocaleCompare(filename,"-") != 0)
    {
      status=GetPathAttributes(filename,&attributes);
      if ((status == MagickFalse) || (S_ISDIR(attributes.st_mode) != 0))
        {
          ThrowFileException(exception,BlobError,"UnableToReadBlob",filename);
          return(NULL);
        }
      file=open_utf8(filename,O_RDONLY | O_BINARY,0);
    }
  if (file == -1)
    {
      ThrowFileException(exception,BlobError,"UnableToOpenFile",filename);
      return((unsigned char *) NULL);
    }
  offset=(MagickOffsetType) lseek(file,0,SEEK_END);
  count=0;
  if ((file == fileno(stdin)) || (offset < 0) ||
      (offset != (MagickOffsetType) ((ssize_t) offset)))
    {
      size_t
        quantum;

      struct stat
        file_stats;

      /*
        Stream is not seekable.
      */
      offset=(MagickOffsetType) lseek(file,0,SEEK_SET);
      quantum=(size_t) MagickMaxBufferExtent;
      if ((fstat(file,&file_stats) == 0) && (file_stats.st_size > 0))
        quantum=(size_t) MagickMin(file_stats.st_size,MagickMaxBufferExtent);
      blob=(unsigned char *) AcquireQuantumMemory(quantum,sizeof(*blob));
      for (i=0; blob != (unsigned char *) NULL; i+=count)
      {
        count=read(file,blob+i,quantum);
        if (count <= 0)
          {
            count=0;
            if (errno != EINTR)
              break;
          }
        if (~((size_t) i) < (quantum+1))
          {
            blob=(unsigned char *) RelinquishMagickMemory(blob);
            break;
          }
        blob=(unsigned char *) ResizeQuantumMemory(blob,i+quantum+1,
          sizeof(*blob));
        if ((size_t) (i+count) >= extent)
          break;
      }
      if (LocaleCompare(filename,"-") != 0)
        file=close(file);
      if (blob == (unsigned char *) NULL)
        {
          (void) ThrowMagickException(exception,GetMagickModule(),
            ResourceLimitError,"MemoryAllocationFailed","`%s'",filename);
          return((unsigned char *) NULL);
        }
      if (file == -1)
        {
          blob=(unsigned char *) RelinquishMagickMemory(blob);
          ThrowFileException(exception,BlobError,"UnableToReadBlob",filename);
          return((unsigned char *) NULL);
        }
      *length=(size_t) MagickMin(i+count,extent);
      blob[*length]='\0';
      return(blob);
    }
  *length=(size_t) MagickMin(offset,(MagickOffsetType)
    MagickMin(extent,SSIZE_MAX));
  blob=(unsigned char *) NULL;
  if (~(*length) >= (MaxTextExtent-1))
    blob=(unsigned char *) AcquireQuantumMemory(*length+MaxTextExtent,
      sizeof(*blob));
  if (blob == (unsigned char *) NULL)
    {
      file=close(file);
      (void) ThrowMagickException(exception,GetMagickModule(),
        ResourceLimitError,"MemoryAllocationFailed","`%s'",filename);
      return((unsigned char *) NULL);
    }
  map=MapBlob(file,ReadMode,0,*length);
  if (map != (unsigned char *) NULL)
    {
      (void) memcpy(blob,map,*length);
      (void) UnmapBlob(map,*length);
    }
  else
    {
      (void) lseek(file,0,SEEK_SET);
      for (i=0; i < *length; i+=count)
      {
        count=read(file,blob+i,MagickMin(*length-i,(size_t) SSIZE_MAX));
        if (count <= 0)
          {
            count=0;
            if (errno != EINTR)
              break;
          }
      }
      if (i < *length)
        {
          file=close(file)-1;
          blob=(unsigned char *) RelinquishMagickMemory(blob);
          ThrowFileException(exception,BlobError,"UnableToReadBlob",filename);
          return((unsigned char *) NULL);
        }
    }
  blob[*length]='\0';
  if (LocaleCompare(filename,"-") != 0)
    file=close(file);
  if (file == -1)
    {
      blob=(unsigned char *) RelinquishMagickMemory(blob);
      ThrowFileException(exception,BlobError,"UnableToReadBlob",filename);
    }
  return(blob);
}

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.