RPC DCOM WORM (MSBLASTER)
This RPC DCOM worm started spreading early afternoon EDT (evening UTC). At this point, it is spreading rapidly.
NOTE: PRELIMINARY. Do not base your incidents response solely on this writeup.
Increase in port 135 activity: http://isc.sans.org/images/port135percent.png
In order to protect yourself, you need to :
Close port 135 (if possible 135-139, 445 and 593)
Apply Patches http://www.microsoft.com/technet/security/bulletin/MS03-026.asp
If you are infected:
- disconnect machine from any network
- delete msblast.exe - delete registry key staring msblast.exe - reboot.
The worm may launch a syn flood against windowsupdate.com on the 16th. It has the ability to infect Windows 2000 and XP.
The worm uses the RPC DCOM vulnerability to propagate. One it finds a vulnerable system, it will spawn a shell on port 4444 and use it to download the actual worm via tftp. The exploit itself is very close to 'dcom.c' and so far appears to use the "universal Win2k" offset only.
Infection sequence: 1. SOURCE sends packets to port 135 tcp with variation of dcom.c exploit to TARGET
2. this causes a remote shell on port 4444 at the TARGET
3. the SOURCE now sends the tftp get command to the TARGET, using the shell on port 4444,
4. the target will now connect to the tftp server at the SOURCE.
The name of the binary is msblast.exe. It is packed with UPX and will self extract. The size of the binary is about 11kByte unpacked, and 6kBytes packed:
MD5sum packed: 5ae700c1dffb00cef492844a4db6cd69 (6176 Bytes)
So far we found the following properties:
- Scans sequentially for machines with open port 135, starting at a presumably random IP address
- uses multiple TFTP servers to pull the binary
- adds a registry key to start itself after reboot
Name of registry key:
SOFTWARE\Microsoft\Windows\CurrentVersion\Run, name: 'windows auto update'
Strings of interest:
I just want to say LOVE YOU SAN!!
billy gates why do you make this possible ? Stop making money and fix your software!!
tftp -i %s GET %s
windows auto update
Existing RPC DCOM snort signatures will detect this worm. The worm is based on dcom.c
Those who do not understand Unix are condemned to reinvent it, poorly.
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