Screaming Penguin - Source Does Matter

Microsoft has released another security bulletin for IIS (4 and 5.) The latest vulnerability, the "Myriad Escaped Character" vulnerability, allows a malicious user to send a "corrupted" URL to the server which can cause the server to stop responding (or crawl, same difference to users.) The "corrputed" URL should be discarded and or not accepted by the server, but it is accepted and it causes major problems. This is obviously not a direct security vulnerability, but it is a serious DoS attack and that is something you literally cannot afford with a web server. The details and the MS announcement are below.

Mini rant mode == 1 : I have a few problems with the frequency of MS exploits. I applaud MS for releasing security advisories and trying to rectify each known issue, but the amount of advisories is overwhelming. I get literally 2 or 3 emails a day from the MS security list relating to one thing or another. This is expected with any computer operating system or software package to some minor degree, but not daily, and not 2 or 3 daily. That is ridiculous and unaccpetable, and one of the reasons I do not use IIS or NT for serious production machines. I like NT, and I like IIS. They are easily configurable and look great, I like easy to configure via a GUI. I wish they performed better. I am not an MS basherby default and I do not criticize anything without a reason. These products deserve criticism, the security and perfomance issues that plague them are unacceptable. Mini rant mode == 0.

Now that I got that sentiment expressed, here is the latest exploit for your IIS stopping enjoyment. Also notice that MS is now using PGP, that is another interesting story in and of itself (Microsoft using what at least WAS a free community tool for security, the CA fiasco aside, again, another story altogether.)

-----BEGIN PGP SIGNED MESSAGE-----

Microsoft Security Bulletin (MS00-023)

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Patch Available for "Myriad Escaped Characters" Vulnerability

Originally Posted: April 12, 2000

Summary

=======

Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) Internet Information Server. The
vulnerability could allow a malicious user to slow a web server's
response or prevent it from providing service altogether for a period
of time.

Frequently asked questions regarding this vulnerability and the
patch can be found at
http://www.microsoft.com/technet/security/bulletin/fq00-023.asp

Issue

=====

Special characters can be embedded in URLs by use of so-called escaped
character sequences. By providing a specially-malformed URL with an
extremely large number of escaped characters, a malicious user could
arbitrarily increase the work factor associated with parsing the
escaped characters, thereby consuming much or all of the CPU
availability on the server and preventing useful work from being
done.

The vulnerability does not provide any capability to cause the server
to fail, or to add, change or delete data on it. The slowdown would
only last until the URL had been processed, at which point service
would return to normal.

Affected Software Versions

==========================