Microsoft notified customers this week it plans to patch a total of 25 security vulnerabilities, five of which received the highest severity rating of “critical,” in its upcoming “Patch Tuesday” release.

Altogether, the company will release 11 Security Bulletins. However, the new bug-fix drop will not be of the scale of October’s patch release, the largest to date for Microsoft.

While Microsoft alerts IT administrators to upcoming Patch Tuesday roundups, it typically does not go into advance detail surrounding the vulnerabilities it plans to address before it’s released the updates.

However, some key details are known of a handful of the problems it’s aiming to fix. Included in the vulnerabilities getting attention on Tuesday are a pair of flaws — one listed as critical — that originally surfaced as Microsoft Security Advisories, which are somewhat akin to early warnings about bugs for which Microsoft doesn’t as yet have patches.

The most dangerous of the two surfaced in early March. That bug has to do with how VBScript processes help files in Internet Explorer.

Among the other critical bugs receiving patches on Tuesday are ones that affect all supported versions of Windows, from Windows 2000 Service Pack 4 (SP4) to Windows XP SP2 and SP3, to Windows Vista SP1 and SP2, and even Windows 7.

Additionally, critical patches affect Windows Server 2003 and 2008 Release 2 (R2). Both 32-bit and 64-bit versions of those systems are included on the list of affected systems.

Other vulnerabilities due for patching, though rated as “important” — the third highest threat level in Microsoft’s four-level vulnerability rating system — affect Microsoft Office and Exchange.