How do viruses spread by open network shares on Windows machines?

I have been reading about the conflicker virus, and wonder about the reference of it infecting distant machines through open network shares. I cannot find a way for a virus to invoke a remote execution to infect a distant machine. Because of Microsoft's "helpful" behavior, I can see how a virus may trick a user into executing it, but I don't see how it can execute itself.  I have Googled and read many discussions, but never found out a specific answer to my question.

The share I am talking about is a data share; the entire drive is NOT shared ,and the OS directories (including OS extensions by installed programs) are not shared.  Clearly, if I share the entire drive, or the OS or Program directory,  an OS or program DLL or EXE can be replaced, and eventually executed by normal calls from the OS.

Possibly the problem is the terms used, spread and infection are being used interchangeably.  In my mind, spreading means the virus payload is being placed on a device, such as a removable storage or shared network directory, but is not active. Infected to me means the virus is active. If a virus just spreads, a good and up-to-date pre-execution virus scanner will block infection.

What concerns me is the implication that a virus can push itself from one machine to another and infect that machine without overt user action on the targeted machine, i.e., not just place a copy of the payload in the shared directory, but actually remotely cause the activation of that payload.

Any insight into this mechanism of infection would be appreciated.

pluskeyAsked:
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xmachineConnect With a Mentor Commented:
Sorry, there is no Windows vulnerability called X, I used it for the example only. There are a lot of vulnerabilities that would fit here.

For example,

http://www.securityfocus.com/bid/31874
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xmachineCommented:
Hi,

Some viruses or worms are being programmed to spread through networks by exploiting X vulnerability in the system. So, once the exploit is successfully executed remotely, the virus's payload will be transfered to the infected machine and get unpacked and decrypted in memory.

Windows admin shares (ADMIN$, C$, IPC$, D$..etc) are used to access and penetrate systems remotely, a virus only needs to infect one system running using a domain privileged account (ex. Domain Administrator) to able to access all systems in the network. That's why we encourage users to be wise when they want to use such powerful privilege.

You need to use shared folders permissions, and auditing to protect against infections. Read-only permission will prevent writing inside these folders (ex. Autorun.inf) or modifying any executable files.

A Symantec Certified Specialist @ your service
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pluskeyAuthor Commented:
Xmachine, thank you for your reply,but I am still confused by the situation.

If I understand you correctly, a networked windows machine with an open share can have a remote execution forced upon it using this X vulnerability.  Can you describe, or give reference to, this vulnerability?  

I Googled  X vulnerability, and only found referenced dated later than 2006 in unpatched windows XP systems, so I didn't find help there. I have found references to Active-X vulnerabilities, not X vulnerability.

I also have been disabling autorun since before XP, because having that enabled seemed to me asking for trouble.  Is that part of the security hole being referenced?

Once again,thank you for your reply.
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pluskeyAuthor Commented:
Thank you for the information and education.  I was completely unaware that Microsoft OS can be exploited by completely remote means, as opposed by trickery of an unsuspecting user.  If I understand your reference, the exploit employs access through a specific TCP port which is used for some Microsift-centric operation to induce remote code operation without any user intervention.  

While I understood the buffer overflow type exploits, I did not know legal command driven exploits existed.
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