Security

PHP md5

var_dump(md5('QNKCDZO') == md5('s878926199a'));
// true

Example

If I only use md5 to hash password,

then I can login with both 'QNKCDZO' and 's878926199a'.

List

var_dump(md5('QNKCDZO'));
// 0e830400451993494058024219903391

var_dump(md5('s878926199a'));
// 0e545993274517709034328855841020

WHY?

PHP is weak typing.

When using '==', it treats the result as numerical strings.

'0e830400451993494058024219903391' would be 0,

and also '0e545993274517709034328855841020',

for they are both started with '0e'.

var_dump(md5('QNKCDZO') === md5('s878926199a'));
// false

hash_equals(md5('QNKCDZO'), md5('s878926199a'));

Solution

Use '===' and it will check types.

 

Or you can use 'hash_equals' function which is timing attack safe.

Broken Access Control

Example

HITCON Zeroday

Change value of cookie, then login to another account.

Example

HITCON Zeroday

Cookie v.s. Session

  • Cookie
    • Saved at browser
    • Send to server each time
    • Users can modify it by themselves
  • Session
    • Saved on server
    • Can be only accessed by server

View cookie

F12 > Storage

Public Data

SITCON 2018: 校園駭客-看你學號() return 你家住址;

Powerful Google

What can you get?

  • A part of one's identity number
  • Full name

You

妹子(?)

What can you get?

  • Class and seat number
  • Student ID

What can you do?

  • Student ID
    • school email
      • ck1071234@gl.ck.tp.edu.tw
      • 10731234@m2.csghs.tp.edu.tw
      • d10730101@gapps.fg.tp.edu.tw

CK?

Calculate Identity Number

Wiki

Calculate Identity Number

A12345XXXX

Known Numbers

Can be calculated

000~999 = Total 1000 combinations

What can you get?

  • Full identity number
  • PE grade
  • Height, weight etc.

What can you get?

  • address
  • birthday
  • email
  • grade
  • family members
  • embarrassing self intro

Thanks for listening!

Made with Slides.com