The company says businesses that haven't done so should look for applications that use RSA certificates that are smaller than 1,024 bits because starting next month updated Microsoft applications won't accept them.
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The result will be that certificate authority services won't work, making it impossible for applications to reach other resources that require the certificates, Microsoft says.
Internet Explorer will deny access to Web sites with smaller keys, Outlook 2010 won't encrypt email and Outlook won't be able to connect to Exchange servers, the company says.
Other platforms affected include Windows XP, Windows Server 2003, Windows Server 2003 R2, Windows Vista, Windows Server 2008, Windows 7 and Windows Server 2008 R2 operating systems.
"[T]his could be a serious issue for a lot of companies because when it breaks your software, it breaks it in a big way," says from Paul Henry, a security and forensic analyst at Lumension.
In an advisory, Microsoft says businesses should examine systems and applications "that have been tucked away to collect dust and cobwebs because they 'still work' and have not had any cause for review for some time." Those are the ones most likely to have shorter certificates; most mainstream applications moved to lengthier ones long ago at the urging of security-standards and best-practices bodies.
The upgrade to stronger security settings has been available since August, but next month Microsoft will issue it as part of its Windows Update cycle.
While the upgrade will boost security and avoid a list of problems, it can cause issues, the company says. Things to look out for:
= Error messages when browsing to web sites that have SSL certificates with keys that are less than 1,024 bits;
= Problems enrolling for certificates when a certificate request attempts to utilize a key that is less than 1,024 bits;
= Difficulties creating or consuming email (S/MIME) messages that utilize less than 1;024 bit keys for signatures or encryption;
= Difficulties installing Active X controls that were signed with less than 1,024 bit signatures;
= Difficulties installing applications that were signed with less than 1,024 bit signatures (unless they were signed prior to Jan. 1, 2010, which will not be blocked by default).
Meanwhile, Microsoft advises that next Tuesday it will have just two Patch Tuesday security bulletins for its customers to deal with. Both are ranked Important, a step down from its most serious bulletins, which are marked Critical.
The first bulleting fixes problems with Microsoft Visual Studio Team Foundation Server 2010 Service Pack 1, which makes the platform vulnerable to elevation of privilege attacks. The second affects Microsoft Systems Management Server 2003 Service Pack 3 and Microsoft System Center Configuration Manager 2007 Service Pack 2 and also addresses elevation of privilege weaknesses.