ONLY NECESSARY for Windows XP and Server 2003Sharable Shortlink
A bit of background:
On Saturday, June 5th, Tavis Ormandy, a security researcher employed by Google, provided acknowledged proof to Microsoft of a previously unpublished and unknown vulnerability affecting the XP and Server 2003 versions of Windows (neither Vista nor Windows 7.)
Then, five days later, breaking from the “Responsible Disclosure” tradition of providing a software publisher time to research and repair the problem prior to disclosing its existence to the world, Tavis did just that in a high visibility posting on Thursday, June 10th.
A predictable fracas has arisen because Tavis’ employer, Google, and Microsoft are increasingly seen as competitors in “the race to the cloud” as personal and corporate computing move from the desktop and into “the cloud” of the Internet and the Web.
For his part, Tavis appears to be no big fan of the Responsible Disclosure paradigm, preferring the “Full Disclosure” approach. Tavis suggests that anyone interested consider the published opinion of the much-respected security researcher and cryptographer, Bruce Schneier:
Tavis attempts to explain that he performed this research — and made this disclosure — on his own behalf and not under the auspices of his employer, Google. But neither he nor Google are getting off so easily. (It occurs to me that he could have easily made the disclosure anonymously if he had wanted the information out there without dragging Google into the controversy. But, for whatever reason, he chose to employ his public persona.) Microsoft has also gone public with their unhappiness, making it clear that Tavis is a Google security researcher.
Why does any of this matter to us?
Unfortunately, the surprising amount of noise created by the details of this disclosure have lifted “just another 0-day vulnerability” (which would be bad enough all by itself) well into the spotlight, making it all the more likely to be exploited. Google News (note the irony) currently finds 207 separate articles on this topic! How can malicious hackers resist this one? They won’t.
And the second bit of bad news is that this is the worst sort of vulnerability: Trivial to cause malicious code to run on the users’ computer, with a public, very complete and thorough description including sample code. Since Microsoft was given very little notice, and since their monthly “Patch Tuesday” occurred just two days before the vulnerability disclosure, it’s unclear whether the world of XP users will need to wait a month, more than a month, or less … But it could be a while.
Therefore, XP users may wish (and would probably be well advised) to immediately disable their system’s “hcp” protocol handler simply by renaming its Key in the Windows registry. (I prefer renaming, Microsoft offers several more complex workarounds. See the link under “Workarounds”.)
If you choose to follow my simple renaming suggestion, do the following:
- Run XP’s “Regedit” registry editor by clicking on “Start” then choose “Run”, enter “regedit” in the Open field, then click “Ok.”
- Find the “HCP” protocol key by searching the registry: Using the Regedit application, select “Edit” from the menu, then “Find…” As shown in the sample below, enter “HCP” into the “Find what:” field, then uncheck “Values” and “Data” and check “Match whole string only”. With the “Find” dialog set as shown below, click the “Find Next” button…
…some time will pass while Windows searches through the registry to locate the “HCP” key…
- Once the search stops, you should see the “HCP” key highlighted as shown below:
Verify that the correct “HCP” is highlighted by checking the lower-left status line which should show “My Computer\HKEY_CLASSES_ROOT\HCP” just like the sample above.
- Right-click on the “HCP” key, choose “Rename” from the pop-up menu, then change the key’s name to “HCP-OFFLINE” (or whatever you like other than “HCP”).
Following the simple instructions above will immediately (no reboot required) eliminate your system’s ability to launch the vulnerable and defective Help Center application in response to an “hcp://” style URL link — now you’re safe. That’s what you want until Microsoft updates and repairs the newly public vulnerability in Windows Help Center.
You can test it too!
If you’re a belt & suspenders sort of person (as I am) you can test your system’s vulnerability to the exploit both with the “HCP” key named “HCP” and also “HCP-OFFLINE” (or whatever you may have named it). Under the “Consequences” section of Tavis’ original posting to seclists.org, he provides proof-of-concept links for users having IE7 and IE8 (and the IE8 link was effective with my Firefox system).
But please remember!, this is admittedly a horrendous kludge that you will need to remember to “undo” — by restoring the renamed HCP key back to “HCP” once Microsoft repairs their code. Still, it’s all we have for now and it’s arguably better than having our machines taken over remotely.