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NetTalk Web Server => Web Server - Share Knowledge => Topic started by: random69 on October 23, 2007, 12:04:23 PM

Title: NOTE: Issue with NetWebServerWorker._Clean in NETWEB.CLW / 4.29
Post by: random69 on October 23, 2007, 12:04:23 PM

There's a bug in the _Clean function such that the entire string may not get cleaned correctly to prevent XSS.

IE. A string "<h1>hello</h1>bogus</div>" returns "&#60;h1&#62;hello&#60;/h1>bogus</div>" which obviously is not correct.

Original Code:

Code: [Select]

NetWebServerWorker._Clean PROCEDURE  (String p_html)
loc:Html  String(NET:MaxBinData)
x long
y long
  code
  loc:Html = p_Html
  x = len(clip(loc:Html))
  y = 0
  loop
    y += 1
    if y > x then break.
    case val(loc:html[y])
    of 60 ! <
    orof 62 ! >
    orof 34 ! "
    orof 35 ! #
    orof 39 ! '
    orof 59 ! ;
    orof 38 ! &
      loc:html = sub(loc:html,1,y-1) & '&#' & val(loc:html[y]) &';' & sub(loc:html,y+1,size(loc:html)-y)
      y += 4
    End
  end
  return clip(loc:Html)
New Code - Note the insertion of x+=4 to increase the len string...

Code: [Select]

NetWebServerWorker._Clean PROCEDURE  (String p_html)
loc:Html  String(NET:MaxBinData)
x long
y long
  code
  loc:Html = p_Html
  x = len(clip(loc:Html))
  y = 0
  loop
    y += 1
    if y > x then break.
    case val(loc:html[y])
    of 60 ! <
    orof 62 ! >
    orof 34 ! "
    orof 35 ! #
    orof 39 ! '
    orof 59 ! ;
    orof 38 ! &
      loc:html = sub(loc:html,1,y-1) & '&#' & val(loc:html[y]) &';' & sub(loc:html,y+1,size(loc:html)-y)
      y += 4
      x += 4 ! offset length since we just inserted more
    End
  end
  return clip(loc:Html)
I would suggest this gets fixed in a subsequent release.

HTH

Title: Re: NOTE: Issue with NetWebServerWorker._Clean in NETWEB.CLW / 4.29
Post by: Bruce on October 29, 2007, 06:21:05 AM

Hi Random,

Thanks for this. I didn't spot this in time to put it in the 4.30 pre-release, but I'll make sure it's in the 4.30 final release (or indeed in the next pre-release if there is one.)

Cheers
Bruce